1990 , Volume , Issue Oct-1990

ingly used at HP for software product development.4'5 The goals of object-oriented methods are very appealing be cause they encourage such practices a...

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H E W L E T T O C T O B E R

HEWLETT PACKARD © Copr. 1949-1998 Hewlett-Packard Co.

1 S 3 O

H E W L E T T - P A C K A R D October 1990 Volume 41 • Number 5

Articles O An Overview of the HP Interactive Visual Interface, by Roger K. Lau and Mark E. Thompson 7 HP I VI Project Management 9 Quality Function Deployment and HP IVI

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21

The HP IVI Object-Oriented Toolkit, by Mydung Thi Tran and David G. Wathen

HP IVI Application Program Interface Design, by Pamela W. Munsch, Warren I. Otsuka, and Gary D. Thomsen 29 Object-Oriented Design in HP IVI

32

HP IVIBuild: Interactive User Interface Builder for HP IVI, by Steven P. Witten and Hai-Wen L. Bienz

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Creating an Effective User Interface for HP IVIBuild, by Steven R. Anderson and Jennifer Chaffee

49 59

26.5-to-75-GHz Preselected Mixers Based on Magnetically Tunable Barium Ferrite Filters, by Dean B. Nicholson, Robert J. Matreci, and Michael J. Levernier

62

HP DIS: Garliepp, Development Tool for Factory-Floor Device Interfaces, by Kent L. Garliepp, Irene Skupniewicz, John U. Frolich, and Kathleen A. Fulton

Hexagonal Ferrites for Millimeter-Wave Applications, by Dean B. Nicholson

65 Finite State Machine 67 Matching Messages 69 Action Routines

Editor, Richard P. Dolan • Associate Editor, Charles L. Leath • Assistant Editor, Gene M. Sadoff • Art Director, Photographer, Arvid A. Danielson Support Anne Susan E. Wright • Administrative Services. Diane W, Woodworth • Typography, Anne S. LoPresti • European Production Supervisor, Sonja Wirth

O Hewlett-Packard Company 1990 Printed in U.S.A.

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Research Reports

~7Q Measurement of R, L, and C Parameters in VLSI Packages, by David W. Quint, Asad I O Aziz, Ravi Kaw, and Frank J. Perezalonso ~7Q Statistical Circuit Simulation of a Wideband Amplifier: A Case Study in Design for / O Manufacturability, by Chee K. Chow

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System Vivek Air Flow Analysis for a Computer System Processing Unit, by Vivek Mansingh and Kent P. Misegades

Departments 4 In this Issue 5 What's Ahead 45 Authors

The Hewlett-Packard Journal is published bimonthly by the Hewlett-Packard Company to recognize technical contributions made by Hewlett-Packard (HP) personnel. While the information of in this publication is believed to be accurate, the Hewlett-Packard Company makes no warranties, express or implied, as to the accuracy or reliability of such information. The Hewlett-Packard Company disclaims all warranties of merchantability and fitness for a particular purpose and all obligations and liabilities for damages, including but not limited to indirect, special, or consequential damages, attorney's and expert's fees, and court costs, arising out of or in connection with this publication. Subscriptions: non-HP Hewlett-Packard Journal is distributed free of charge to HP research, design, and manufacturing engineering personnel, as well as to qualified non-HP individuals, business and educational institutions. Please address subscription or change of address requests on printed letterhead (or include a business card) to the HP address on the please cover that is closest to you. When submitting a change of address, please include your zip or postal code and a copy of your old label. Submissions: research articles in the Hewlett-Packard Journal are primarily authored by HP employees, articles from non-HP authors dealing with HP-related research or solutions contact technical problems made possible by using HP equipment are also considered for publication. Please contact the Editor before submitting such articles. Also, the Hewlett-Packard should encourages technical discussions of the topics presented in recent articles and may publish letters expected to be of interest to readers. Letters should be brief, and are subject to editing by HP. Copyright publication 1 granted copies Company. All rights reserved. Permission to copy without fee all or part of this publication is hereby granted provided that 1 ) the copies are not Hewlett-Packard used, displayed, or distributed for commercial advantage; 2) the Hewlett-Packard Company copyright notice and the title of the publication and date appear on the copies; Otherwise, be a notice stating that the copying is by permission of the Hewlett-Packard Company appears on the copies. Otherwise, no portion of this publication may be produced recording, information in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage retrieval system without written permission of the Hewlett-Packard Company. Please Journal, inquiries, submissions, and requests to: Editor, Hewlett-Packard Journal, 3200 Hillview Avenue, Palo Alto, CA 94304, U.S.A.

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In this Issue Our cover subjects this month can barely be seen in the cover photograph. They're the two tiny specks in the middle of the flat plate in the foreground. They are spheres of barium ferrite that serve as the frequency-sensitive elements of magnetically tunable bandpass filters for the millimeter-wave KP'^Elljllg frequency range. (The millimeter-wave range is the region of the elecrBlOIM becoming spectrum from about 30 to about 300 gigahertz. It's becoming more important as radar, communications, and other systems move to higher frequencies seeking higher performance or less crowding.) These filters are used mixers, a filters in the HP 11974 Series preselected mixers, a family from four mixers designed for down-converting millimeter-wave signals from the 26.5-to-75GHz range into the frequency range of compatible HP spectrum analyzers. The preselection filter removes unwanted image and multiple responses, natural consequences of the mixing process, that desired the spectrum analyzer display and obscure the desired response. In the microwave frequency range, below 30 GHz, yttrium iron garnet (YIG) spheres have been used as resonators in such filters, but at higher frequencies, tuning magnets for YIG spheres begin to pose design problems, so a new material was needed. A new four-sphere filter design was also found necessary to achieve the required performance. The design and performance of the HP 11974 Series preselected mixers are described in the article on page 49. The article on page 59 gives the reasons tells the choice of scandium-doped, M-phase barium ferrite for this application and tells how the spheres are made. Software for computer integrated manufacturing (CIM) is in great demand, and HP development laboratories are responding with a steady stream of new products. Two are featured in this issue. The first, HP Interactive Visual Interface, or HP IVI, uses object-oriented design, the industry-stan dard X software System, and widget technology to help application software developers provide graphical user interfaces for industrial applications. (Widgets are standard pieces of software that produce users' scrollbars, and the like on computer screens.) HP IVI improves its users' productivity in designing user interfaces because it is interactive, facilitates saving and reusing interfaces, and doesn't demand that users know the details of the X Window System or widgets. The article on page 6 gives an overview of HP IVI, which consists of two main parts. Users construct their interfaces using HP IVI's interactive editor, described on page 32, and then activate the objects created with the editor by writing C-language programs using a toolkit of functions provided by HP IVI's application program interface. Details of the application program interface's object-oriented toolkit are in the article on page 1 1 , and the design of the application program interface is the subject of the article on page 21 . In the article on page 39, we're told how the HP IVI with own user interface was refined and given a 3D appearance with the help of a team of industrial designers. The other CIM software product in this issue is HP Device Interface System, or HP DIS. It addresses the problem of efficiently developing interfaces between computers and factory-floor devices because robots, programmable controllers, and machine tools. This is a problem because these different, typically come from many manufacturers and have different, proprietary interfaces. HP DIS is a between that helps application software developers create and test interfaces between HP 9000 provides and factory-floor devices. Its development facility provides a high-level lan guage provides a communications protocols. Its testing facility provides a test generator, a test exerciser, and a device simulator that makes it unnecessary to have actual devices to test interfaces. The HP DIS run-time facility executes protocols in real time. The design and perfor mance of HP DIS are described in the article on page 62.

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Simulation is an important part of many design processes because it makes it possible to refine a design simulation actually building anything, provided that the computer model used for simulation accurately reflects the behavior of the device or system being designed. Engineers at HP's Colorado a Circuits Division wanted to verify the accuracy of the electrical models of a 408-lead made ceramic package for a large integrated circuit chip. The models were made up of discrete inductances, capacitances, and resistances. To verify the models, these parameters had to measurement methods on a real package. When traditional high-frequency measurement methods proved paper new methods were developed. These methods are the subject of the paper on page 73. In integrated circuit design, the objective of simulation is sometimes to predict, in the design phase, in statistical distributions of a circuit's performance parameters in production. A problem is that 1C parameter variations aren't all completely random, as they are assumed to be by commercially available circuit simulators. Those within a chip, such as side-by-side resistor values, are highly correlated, and failure to take this into account leads to inaccurate simulations. In the study reported in the paper on page 78, this problem was solved by applying principal component analysis, a branch of multivariate statistics. Each circuit parameter was expressed in terms of a set of then random variables. The independent variables were then used as the inputs to the circuit simulator program, and the results were later converted to circuit parameter data. Another application of simulation, this time to predict the pressure drop and air flow characteristics in a computer system processing unit, is described in the paper on page 82. In the past, these quantities have been determined from measurements on prototype machines, which are available only after most of the design has been done. If the measured results are unacceptable, major design finite may be required. The study showed that, using supercomputers and finite element modeling, it is possible to simulate the air flow accurately enough to allow meaningful decisions early in the design phase. P.P. Dolan Editor

Cover The flat plate in the foreground is the iris plate from a magnetically tuned preselection filter used of tiny HP 1 1974 Series preselected mixers. In the middle of the plate are two tiny barium ferrite the spheres. Also shown are the top and bottom halves of the tuning magnet, the magnet body, and the two parts of the waveguide assembly.

What's Ahead In the December issue, we'll have articles on the autochanger and servo design and system integration of HP's 20-Gbyte rewritable optical disk library system, designed for direct access secondary storage. Error correction, software protection, and system integration of HP's CD-ROM drive controller also be featured. The data communications and terminal controller for HP 3000 computers running the MPE XL operating system now supports X.25 network packet assembler/dis assemblers; two articles will deal with this capability. We'll also have a research report on anisotropic dimensional changes in cold-drawn copper beryllium alloy as a result of aging.

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An Overview of the HP Interactive Visual Interface The HP Interactive Visual Interface (HP IVI) product uses object-oriented and window technologies to provide interactive and programmatic tools for building graphical user interfaces. by Roger K. Lau and Mark E. Thompson IN THIS AGE OF INFORMATION, creating effective user interfaces for industrial automation applications is a greater challenge than it has ever been. The right details from a vast array of information must be shown in the appropriate form to the intended group of viewers. In ad dition, the information that is communicated must be con veyed in such a manner as to enhance the decision making process. It often takes more time to develop the interface than it takes to develop any other part of an application. HP Interactive Visual Interface (HP IVI) is designed to help developers provide the type of user interface needed for industrial applications. HP IVI is a user-interface development tool built on the X Window System Version 11 and runs in the HP-UX operating system environment. It consists of two main parts: an interactive editor (HP IVIBuild) and an application program interface (API). Users construct their symbols and displays with HP IVIBuild (the builder) and write a C pro gram using the API calls to call up and activate the windows and other objects created with the builder. An application's user interface can be constructed without the assistance of HP IVIBuild, but with it productivity is greatly increased by the ability to create the interface interactively. HP IVI is also one of the few products to combine at the builder level the power of a graphical presentation with the flexi bility and interactivity of widgets (e.g., pushbuttons, scrollbars, and toggle buttons).1 This article describes some of the market research and the target customers for HP IVI, and provides an overview of the two main components of HP IVI, HP IVIBuild and the application program interface.

tions require graphical user interfaces, and the use of graphics on the factory floor is growing and being applied to monitoring production processes and data gathering. The requirements are performance, reliability, and the in tegrity of data from a workcell. To satisfy these demands, the HP IVI product: • Minimizes the user's expense for the development of user interfaces • Provides a distributable user interface for improved cost, performance, and flexibility • Offers windowing functions and dynamic data config uration • Integrates graphics and widgets intelligently • Gives software engineers the productivity boost needed for them to remain competitive • Ensures top performance and reliability • Gives the user full control over data from the factory floor • Builds on standards. Early in the project, the HP IVI project team used a technique called quality function deployment (QFD) to help analyze customer needs in the industrial automation area. This research helped to define the features for HP IVI. The box on page 9 provides more information about QFD and its use by the HP IVI team. HP IVIBuild

HP IVIBuild is the interactive window and symbol build(continued on page 8)

HP IVI Build Builder Code API Functions

Market Research

The main customers of HP IVI are software engineers who build industrial applications. This includes system integrators, independent software suppliers, and end users with internal software engineering groups. These users benefit by being able to customize screens to their custom ers' applications and by being able to reuse the symbols they created and saved in previous applications. HP IVI also buffers its users from having to know the details of the intrinsics of both the X Window System and widgets. This is considered to be a benefit and a boost to productiv ity. Market research indicates that manufacturing applica

User Interface Objects (Windows, Symbols, etc.)

Objects Created by HP IVI Application

API Functions API = Application Program Interface

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Fig. 1. HP IV! 'Build is used to create user interface objects that are saved in a file, and a user application uses the API functions to retrieve and manipulate the objects.

HP IVI Project Management The HP Interactive Visual Interface project was a relatively large software project (100 KNCSS) and as such it was faced with some interesting challenges during product development. Besides the normal challenges associated with software project management (e.g., version control, code inspections, project standards, and schedule deadlines), HP IVI was faced with three main challenges: determining the exact customer needs before design and implementation, using existing software, and using new software development technologies. For determining cus tomer needs, a process called quality function deployment (QFD) was used. This process helped us to determine the feature set for HP IVI (see box on page 9). The existing software was a combination of software from other HP entities and from outside vendors. Finally, the new technologies included the use of objects and windows for design and implementation. Existing Software One of the primary goals of HP IVI was to leverage the work of others. The decision to use existing software resulted from the desire to decrease the time to market for the product by reducing the engineering time and effort involved in design, implementa tion, and support. There was also a need to base HP IVI on components that conform to standards (explicit or de facto). To these ends, the basic framework of HP IVI is based on software that was purchased as well as software that was produced by other entities in Hewlett-Packard. The HP IVI project team realized the benefits that could be obtained by leverage early on. The basic object-oriented framework, the error handling routines, the X1 1 client library and server, the X toolkit, and the HP X widget set were all the work of others. While we certainly achieved our goals of reducing design, implementation, and support costs, we missed our orig inal time-to-market goals. Following are some of the lessons we learned about leveraging existing software. • The If and stability of existing code is a critical factor. If there are many defects in this code, much time will be spent isolating the problem and negotiating with the software su pplier to have it repaired .This can wreak havoc with a project schedule. One way around this is to obtain the source code for the underlying software and make the repairs locally. This may provide the most timely solution, but also raises many supportability questions. • Negotiating enhancements to the existing software may be difficult. Priority lists may not mesh well between vendor and receiver. Important enhancements in the underlying software may be delayed because of this. • Performance of a product may be adversely impacted by exist ing software. If this is the case, lobbying for improvements may be time-consuming and marginally successful. • Good documentation of existing software is essential for a product to be successful. Inadequate or inaccurate documen tation can also impact schedules. • It is very important to establish a good line of communication and a strong working relationship with the existing software supplier. Changes made to their product may have drastic effects on the local product. It is important to learn about changes as early as possible (i.e., at the investigation phase rather than at the release phase). Project teams that leverage a large amount of software from other sources should be very careful not to assume that leverag

ing means that less attention can be paid to producing a very detailed design. Leveraging software does not mean there is no cost associated with it. Engineers have to learn and understand the code, design impacts must be assessed, and the leveraged code must be supported over the life of the product. Also, leveraging product components does not automatically ensure a faster time to market. New Technologies HP IVI is an object-oriented system that is based on the widget technologies and the X Window System. Through the QFD pro cess we found that building on a standard software platform is viewed as an important requirement by our target market. At the start of the HP IVI project no one on the team had any experience with object-oriented programming and design and only one person was familiar with window systems. Therefore, we had to develop a process to disseminate technical information and promote technical expertise among the project team very quickly. This was accomplished through training, the exchange of information during design and code reviews, and the simple sharing of expertise among the project team. The following observations come from our experience with object-oriented programming and design: • Careful consideration should be given to mapping object classes to source code files. The consequences can be fre quent file access conflicts when changes are made to a file. • The temptation to redo class hierarchies should be controlled. Developers must be careful to make practical choices on when the class hierarchies are sufficient. • First-time users should not expect magic. We believe that there was a significant learning curve involved in our decision to use object-oriented programming and design. • Once the learning curve is overcome, the object paradigm is a natural and productive one to use for developing software products. • Object-oriented programming and design have a technical jargon that might mystify developers and their managers at first. Therefore, familiarity with and consistent use of terminol ogy must be established at the start of the project. • The object paradigm is not applicable to all software engineer ing projects. Knowing when to reject this technology in favor of a procedure-based design is important. The use of multiple new technologies in a project with few team members having experience in any of these technologies does have its problems and can be a significant factor on the schedule because it is difficult to anticipate problems and avoid pitfalls. However, using new technologies on a project can be a significant motivator to the engineering staff. Benefits and risks of the inclusion of new technology in any product development effort must be weighed carefully. Chuck Robinson Section Manager Industrial Applications Center Robin Ching Project Manager Industrial Applications Center

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er of HP IVI. It is an API application because it uses the HP IVI API library of C functions to handle both the visual and the nonvisual aspects of creating objects such as man aging object data structures and performing operations re quired to manipulate objects. Consequently, the windows and models created and saved by the builder can be restored by an API program and vice versa (see Fig. 1). For the most productive use of HP IVI, the user first creates the windows needed by an application using HP IVIBuild and then mobilizes the created windows using a C program contain ing API functions. Fig. 2 shows an application user inter face being created with HP IVIBuild. Although an entire HP IVI application could be written using just the API C functions, HP IVIBuild provides the following advantages over this method: • No initial programming is required. • The user can look at the user interface and manipulate it while creating it. • The interface can be altered very quickly. • Several graphical conveniences are available such as snapping to a grid and a simple method of creating ellipses. • An API program that uses HP IVIBuild-created objects is much simpler than one that creates the same objects from scratch. • Symbols created in an HP IVIBuild session can be saved and reused. The articles on pages 32 and 39 provide more information about HP IVIBuild. Objects and API

Since HP IVI is an object-oriented system, all operations are done with objects, resulting in a system that is a hierar chy of objects. Building this hierarchy starts with creating

window objects (windows on the display) and then placing graphics and widget objects into the windows. To activate the objects in the window (i.e., give them dynamic proper ties) some of the attributes of the objects can be changed (e.g., foreground or background color, visibility, or fill per centage for a rectangle). When an application uses objects to display data values, it can make calls to the API functions to update the data values in the objects displayed in the windows. The objects used in HP IVI are categorized into four hierarchical layers: • High-Level Objects. These objects specify global attri butes for the other levels of objects. This level includes the window and model objects mentioned earlier. • Composite Objects. These are organizational groupings of primitive objects. This includes menus and their com ponent menu panes, row-columns, and scroll lists. • Primitive Objects. These are basic widgets and graphics objects — the basic visual pieces that make up the display. Graphics primitives include items such as polylines, splines, arcs, rectangles, and circles. Widget primitives include pushbuttons, toggle buttons, text widgets, textedit widgets, menu buttons, and scrollbars. Both types of primitive objects can receive input from the user. • Low-Level Objects. These are mostly nonvisual objects that are used to specify certain object attributes. Objects that handle object data structures and objects that handle events are examples of low-level objects. Because an object hierarchy is used, displays can be created from the top down (parent to child) or the bottom up (child to parent), giving the designer a lot of flexibility in implementation. Certain objects can be gathered and arranged by making them into children of composite ob(continued on page 10)

Fig. 2. An application user inter face being created using the in teractive tools provided by HP IVIBuild. The tool box, utility box, and line width panels are HP IVIBuild components.

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jects. Composite objects can be used to organize and add extra control over their descendant objects. For example, a row-column object can be used to organize different widget primitives into rows and columns. All objects in the hierarchy have attributes (e.g., color, size, shading, etc.). It is through the control of these attri butes that the displays created with HP IVI get their dynamic quality. One can easily manipulate several attri butes on an object with a single API function call, changing location, color, visibility, or some other attribute. Other API function calls enable the developer to: • Create and free objects • Manipulate object attributes • Save and restore objects • Locate objects • Obtain user input from primitive objects • Perform visual updates of the display • Manipulate lists of objects. As an example, callback objects can be attached to any visual object and cause a callback function to be called whenever a predefined event (such as clicking on the mouse button or depressing a key on the keyboard) occurs. The callback function can be used to obtain and manipulate data from the shop floor and modify attributes of objects

on the display (e.g., changing an object's color from green to red or changing the textual information displayed in an object). The API functions and the internal design of these functions are described in the articles on pages 1 1 and 21. Conclusion

HP IVI facilitates the design and implementation of one of the most important parts of any manufacturing applica tion — its interface to the user. The benefits of the window ing technology of Xll are just beginning to be realized on the manufacturing floor. HP IVI is one of the first integrated applications to bring the X Windows technology to the factory floor. The combination of widgets and graphics gives the application designer more freedom to present the needed information in the fashion best suited for its in tended viewers. This design freedom promotes the kind of informed decision making needed in today's fast-paced and highly competitive industrial marketplace. References 1. D.L. McMinds and B.J. Ellsworth, "Programming with OSF/ Motif Widgets," Hewlett-Packard Journal, Vol. 41 , no. 3, June 1990, pp. 26-35.

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The HP IVI Object-Oriented Toolkit Using object-oriented design techniques, a minimum set of functions is provided with the HP IVI product for manipulating widgets and graphic objects to create a graphical user interface. by Mydung Thi Tran and David G. Wathen THE HP IVI APPLICATION PROGRAM INTERFACE [API] is an object-oriented toolkit of C functions that enable a software developer to create an interactive and informative graphical user interface programmatically. The API functions can be used for any application in which a highly interactive graphical user interface is required. The collection of API functions provides the ability to build different models of user interfaces that can be saved and used again in other user interfaces. High-level objects pro vide the control and organization necessary to support lower-level composite and primitive objects. All objects have configurable attributes or characteristics that make it possible to customize the look and feel of a particular ob ject. Color, size, and font are a few examples of these attri butes. The API functions allow a programmer to do things like create and free objects, query attributes, save and re store objects, get input, and find objects by location. This article describes the the API functions and the arti cle on page 21 describes the internal design supporting these functions.

the display. There can only be one system object per appli cation. All other objects (except low-level objects) are de scendants of the system object. The direct descendant of a system object must be a server object. A server object is the interface to the display system. Information regarding the display and its physical charac teristics is stored in this object. The server object establishes the link between the display device (an XI 1 server) and the user application (the client). Just like the system object, there can only be one server object per application. Win dows are the only children of the server object. Window objects represent the drawable region of the display. A window is an area on a display that connects the world coordinate system (e.g., inches, mm, etc.) defined for a window to the device coordinates (i.e., pixels) of the display system. The window can be seen as a viewport into the world coordinate system. An application can have any number of windows. They can overlap one another and they can be manipulated using a window manager or System (High-Level)

The API Object Hierarchy

All the components of an API application are separate objects that are combined together in a hierarchical arrange ment to form a working user interface. An example of this hierarchical relationship is shown in Fig. 1. This relation ship is described in terms of ancestry. For instance, Model 12 in Fig. 1 is the parent of three children: Model 21, a rect angle, and a row-column object. Another way of saying this is that Model 12 is the ancestor of three descendants: Model 21, a rectangle, and a row-column object. Every API object belongs to one of four groups: high-level objects, composite objects, primitive objects, or low-level objects. Fig 2 lists the different API object groups. High-Level Objects. These objects control and organize groups of objects and hold global resources that help define other objects in the hierarchy. The high-level objects must be created in a specific order: system object, server object, window objects, and model objects. Before anything can be displayed, at least one of each of these objects must be available. Since these objects are required for every appli cation, the API will create default high-level objects if they are not explicitly created. The system object is the highest object in the API object hierarchy. This object stores global attributes that affect the input loop, the update pass, and global resources. The input loop is composed of the code that handles user input and an update pass is the process of flushing changes to

Server (High-Level) Window (High-Level)

Model 12 (High-Level)

Model 11 (High-Level) Circle (Primitive)

Model 21 (High-Level)

Rectangle (Primitive)

Row-Column • Text (Composite) • (Primitive)

Toggle Button (Primitive)

Row-Column (Composite)

Text (Primitive)

Pushbutton (Primitive)

Fig. 1 . The API object hierarchy of a simple application.

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the API functions. The last high-level object, the model object, is the only valid child of a window object. The model object allows an application to put composite, primitive, or other model objects into a single group or collection. When these objects are grouped together, func tions can be performed on them as if they were a single object. At the same time, each part will retain its individu ality. Models can represent a symbol or template that can be saved and restored as many times as desired. Models can have other models, composites, or primitive objects as children. Primitive Objects. These are basic visual objects that are part of one of two categories: graphic primitives or widget primitives. The graphic primitives are visual objects (e.g., circles, rectangles, and arcs) that can receive mouse input. An application can use these objects for graphically repre senting user-oriented objects that display crucial informa tion such as liquid levels and temperature. The widget primitives (e.g., pushbuttons, scrollbars, and text edits) are also visual objects. However, unlike the graphics primi tives, widget primitives can receive keyboard input as well as mouse input. The widget primitives are used for display, text editing and input, and selection capabilities. Primitive objects have no children. Composite Objects. These objects provide the means to organize and manage other objects. Specifically, composite objects make it possible to group primitive widget objects and other composite objects so that they can be manipu lated as a single object. A function or attribute specified for a composite object affects its children without actually changing them. For example, erasing or redrawing a rowcolumn object will cause all its children to be erased or redrawn automatically. Low-Level Objects. These are objects that are not directly visible like primitive or composite objects. They are stand alone objects that are used to specify attribute values for primitive, composite, or high-level objects. Low-level ob jects are used to set attributes for the other three object groups, apply API functions to a list of objects, or deal with user input from the activated objects.

Polymorphism and API

One of the key features of object-based systems is the concept of polymorphism. Polymorphism allows different objects to share a common operational interface (operations with the same name). When an operation is invoked, the function dynamically determines the object type and exe cutes the appropriate code. Object-oriented programs are polymorphic because they can operate on many different object types with the same functional interface. This com mon interface provides a great deal of flexibility and ease of use to the API programmer. Common access reduces the number of functions and increases the power provided by the basic set of functions. The API functions provide the functionality of polymorphism through an identifier called Zlld. When an object is created via the ZtCreate function, a Ztld is returned from the call for use in further operations. The Ztld is a pointer to the object that was just created. This handle allows the programmer to reference the object when addi tional modifications are necessary. The API functions use this identifier to determine the type of object being manipu lated. Attributes and Arglists

Associated with API objects are attributes that describe properties of these objects. Examples of object attributes include properties that define appearance characteristics such as colors and fill patterns for graphic objects, and font, highlight area, and 3D shadowing for widget objects. There are also coordinate system attributes that control the position and sizing of objects, including their point, height, width, scale, rotation, and translation. Table I lists the categories of API attributes. There is a specific list of attributes assigned to each API object type. Users can set these attributes to desired values or can query the values contained in them through a data structure called an Arglist. An Arglist is a variable-length array of attribute-value pairs. The following is the C structure declaration for an attribute-value pair. struct ZtArgListStruct { ZtAttributeType ZtAttribute; ZtValueType ZtValue; typedef struct ZtArgListStruct ZtArgListltem; /*where:

*/

/ ZtAttribute is the defined attribute

*/

/ ZtValueType is defined as a pointer to a / variable containing the attribute value

Fig. 2. API object groups.

*/

Arglists are used to define attributes of objects or functions. Some of the advantages of using Arglists include: • Arglists free users from fixed parameters in a function call. The number of attributes that the user can pass as param eters can vary. • The number of function calls can be minimized by in cluding multiple attributes in the Arglist as opposed to having to use one function call per attribute change. • Attributes can be initialized in the Arglist either statically or dynamically (at run time).

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Table I Categories of API Attributes C a t e g o r y

Trickle-Down

Color, Font, Raster

Attributes that affect or define the current API object hierarchy (e.g.,ZtCHILD_LIST,ZtCURRENT_ MODEL).

Keyboard Traversal

Attributes that assign the input focus to an object (e.g., ZtTRAVERSAL, ZtNEXT_TOP_WINDOW).

Function

Attributes that affect the capa bilities of functions (e.g., ZtRECURSIVE,ZtMERGE).

D e s c r i p t i o n

General Attributes that are common to most objects. For example, the object name (ZtNAME), an object's visibility status (ZtVISIBLE), and user data (ZtUSEFLDATA). Coordinate System

Parenting

These are attributes that define: • Size and position such as an object's height and width (ZtHEIGHTandZtWIDTH) • Transformation, such as an object's rotation, scaling, and translation characteristics (ZtROTATE, ZtSCALE, ZtTRANSLATE) • Normalized device coor dinates for placing windows (ZtXMIN,ZtXMAX,ZtYMIN,ZtYMAX) • Aspect ratio of window device coordinates (ZtADJUST, ZtXADJUST, ZtYADJUST) • Aspect ratios of server objects (ZtXPIXELS, ZtYPIXELS). Attributes that affect the descendants of objects (ZtVISIBLE, ZtSENSITIVE). Attributes that specify the object's color, font, or raster. • Raster lists (ZtRASTEFLLIST) • An object's color (e.g., ZtBACKGROUND_COLOR, ZtFOREGROUND_COLOR,etc.)

API Functions Because of polymorphism a minimum number of API functions are required for manipulating API objects. Polymorphism allows the same API function to be used to handle more than one object. Table II shows the API func tions available for manipulating the object groups shown in Fig. 2. Table II Categories of API Functions Function Use

Function Names

Create and Free Objects ZtClone, ZtCreate, ZtCreateList, ZtFree Manipulate Attributes ZtChange, ZtQuery Save and Restore Objects ZtSave, ZtRestore Locate Objects ZtFindByAttribute, ZtFindByLocation

• An object's font (ZtFONT) • An object's raster (e.g.,ZtFILL_ RASTER, ZtlCONLRASTER).

Pattern and Line

Attributes that control the appearance of borders, lines, and fills (e.g., ZtFILLjriLE, ZtBACKGROUND_TILE, ZtLINE_WIDTH).

Widget Appearance

Attributes that define a widget's appearance (e.g., ZtSHADOW, ZtBOTTOM_SHADOW_COLOR, ZtTOP_SHADOW_ COLOR).

Callback

Attributes used to attach userdefined functions to an object. These functions are used to respond to user input. For example, ZtREASON specifies when a callback function should be called, and ZtCALLBACK_FUNCTION specifies a function for processing user input.

Receive Input ZtDo(..,ZtlNPUT,..) Perform Visual Updates ZtDo(..,ZtDRAW,..) ZtDo(..,ZtERASE,..) ZtDo(..,ZtFLASH,..) ZtDo(..,ZtLOWER,..) ZtDo(..,ZtRAISE,..) ZtDo(..,ZtREDRAW,..) ZtDo(..,ZtUPDATE,..)

Manipulate Lists

ZtCheckListObject, ZtCountLisl, ZtGetListlndex, ZtGetustObject, ZtGetustTail, ZtlnsertListlndex, ZtlnsertListObject, ZtlnsertustTail, ZtMergeListlndex.ZtMergeListTail, ZtMergeListObject, ZtRemoveListlndex, ZtRemoveListObject, ZtRemoveListTail, ZtReplaceListlndex.ZtReplaceListObject, ZtReplaceListTail

Manipulate Arglists

ZtFreeArgList

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Create and Free Objects Objects are created using the function ZtCreate. Any attri butes that are required to be different from the defaults can be passed in the object ArgList when calling ZtCreate. For all the attributes not included in the object ArgList, the API will automatically set them to defaults. Once an object exists, multiple copies of this object can be made by cloning it with the function ZtClone. ZtClone also allows the users to alter some of the attributes of the newly cloned objects in the same call. The following example shows the creation of two text objects with one fixed size, different text strings, and differ ent positions on the display. Fig. 3 shows the data organi zation resulting from this example.

Text Objects (ZITEXT_OBJ)

Point Objects

(ZtPOINT_OBJ)

text1_ld

text2 Id

intreturn_val; Ztldtext1_ld,text2_ld, pointld; / object identifiers */

Fig. 3. Data organization for text objects created with the function ZtCreate or ZtClone.

/ arglistfortextobject(containingattribute-valuepairs) */ static REAL64h,w; static ZtArgListltem textArglist [] =

intreturn_val; (ZtValueType)&h, /

text height

Ztld textUd, text2_ld, pointld; / object identifiers*/

ZtWIDTH,

(ZtValueType)&w, /

text width

/ arglistfortextobject(containingattribute-valuepairs */

ZtPOINT,

(ZtValueType)NULL, /

Ztldforpoint

ZtSTRING,

(ZtValueType)NULL, /

textstring

ZtHEIGHT,

The text Arglist and the point Arglist are the same as in the

NULL, (ZtValueType)NULL

previous example. arglist for point object /

static REAL64 x, y;

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static ZtArgListltem cloneArglist [] =

static ZtArgListltem pointArglist [ ] = {

{ ZtX, (ZtValueType)&x,

ZtPOINT, (ZtValueType)NULL,

ZtY, (ZtValueType)&y,

ZtSTRING, (ZtValueType)NULL,

NULL, (ZtValueType)NULL ;

NULL, (ZtValueType)NULL

} / create reference point for objects x = 10.0 = 10.0;

• The reference points and the first

pointld = ZtCreate(ZtPOINTJDBJ,pointArglist, NULL);

• text object are created the same as • in the previous example.

/ setup to create first text object with height = 20 and

create the second text object at (1 0,60) using the

/ width = 40

ZtClone function y = 60.0;

h = 20.0; w = 40.0; textArglist[2].ZtValue = (ZtValueType) pointld;

return_val = ZtChange (pointld, pointArglist, NULL);

textArglist[3].ZtValue = (ZtValueType) "Firsttext object";

cloneArglist[0].ZtValue = (ZtValue Typejpointld; cloneArglist[1].ZtValue = (ZtValueType) "Second text object"

/ create the first text object textUd = ZtCreate (ZtTEXT.OBJ, textArglist, NULL); / change point components

/

y = 60.0;

text2_ld = ZtClone (TextUd, cloneArglist,

return_val = ZtChange (pointld, pointArglist, NULL);

NULL);

c r e a t e s e c o n d t e x t o b j e c t a t ( 1 0 .

0 , 6 0 . 0 )

* /

textArglist[3].ZtValue = (ZtValueType) "Second text object"; text2_ld = ZtCreate (ZtTEXT_OBJ, textArglist, NULL);

/ free point object if it is no longer needed */ ZtFree (pointld, NULL);

/ free point object if it is no longer needed */ ZtFree (pointld, NULL);

Instead of calling ZtCreate twice, the function ZtClone can be used to create the second text string object:

ZtClone is particularly useful for models and composite objects. With one call, the model or the composite object and its descendants can be duplicated. A call to ZtClone can be modified to control the depth of cloning for a list of objects. In the following example there are two model oh

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jects that have identical properties except for the back ground and foreground colors. The first model object has been created with the child list model! Id. Instead of repeating the same process for the second model mode!2ld, ZtClone is used with the function Arglisl containing the ZtRECURSIVE attribute set to TRUE. The call ZtChangeQ changes the colors.

is changed for all objects referenced by the identifier listld. * arglist for foreground color * static ZtArgListltem fgcArglist [ ] = ZtFOREGROUND.COLOR,

(ZtValueType)NULL,

NULL,

(ZtValueType)NULL

intreUval; Ztldmodellld, model2ld;

int return_val;

/ objectArglistforcolors */

fgcArglist[0].ZtValue = (ZtValueType) steelblue

static ZtArgListltem colorArglist [] =

/ Steelblue is the index into the system object's color list

{

/ (the ZtCOLOR_LIST attribute on the ZtSYSTEMJDBJ). ZtBACKGROUND_COLOR,(ZtValueType)red,

/ change the color to steelblue

ZtFOREGROUNDCOLOR,(ZtValueType)black,

return_val = ZtChange (listld, fgcArglist, NULL);

NULL,(ZtValueType)NULL

}; / functionArglistfor recursive attribute */ static ZtArgListltem recursiveArglist [] = { ZtRECURSIVE,(ZtValueType)TRUE, NULL,(ZtValueType)NULL

model2ld = ZtClone(model1ld, NULL, recursiveArglist);

Default values can also be changed with the same call. To change the value of a default attribute, the object type and not the objectld must be sent to ZtChange. For instance, if at some point in the program it is desired to have all the windows have a red background instead of the default blue, a call could be made to ZtChange with the object type set to ZtWINDOWJDBJ instead of the objectld. Information about the current value of an object's attri butes or the default values can be obtained by making use of the ZtQuery call. If required, API will handle the space allocation for the queried values. The following code frag ment is requesting information on a pushbutton object.

reUval = ZtChange(model2ld, colorArglist, recursiveArglist);

int return_val; char 'querystr;

Cloning nonrecursively (ZtRECURSIVE = FALSE) can be used in cases where objects need to be referenced but copies of these objects are not needed. Fig. 4 shows the data struc ture that would result after nonrecursively cloning the ob jects referenced by the linked list called Listl. Instead of copying the objects, a new linked list (List2) of pointers is created for referencing the objects. The original and newly cloned list will dereference the same objects. HP IVIBuild, the builder component of HP I VI, makes use of this option of ZtClone to duplicate lists of selected objects. The cloned lists are manipulated through the use of list functions to provide the undo and backup capabilities of HPIVIBuild (see page 36). When an object is no longer needed, the function ZtFree can be used to free all memory allocated for the object. Arglists can also be freed using the function ZtFreeArgList. This function will free all memory associated with the Arglist including the additional memory allocated for attributes. Manipulate Attributes Most attributes of existing objects can be modified. For example, in an application in which a text object contains a string that indicates elapsed time, the time needs to be updated periodically. ZtChange can be called passing the new value of the elapsed time in the ZtSTRING attribute of the object Arglist. ZtChange also provides a way to modify several objects in one call. The user simply has to put all the desired objects into a list and issue a ZtChange call on the list object. The changes will be made to all objects that the list refer ences. In the following code fragment the foreground color

/ arglist for querying string static ZtArgListltem qstringArglist [ ] = ZtLABEL_STRING,

(ZtValueType)NULL,

NULL,

(ZtValueType)NULL

A copy of the pushbuttonld's label string will be returned in querystr */ after the ZtQuery call. A return value of FALSE indicates that memory could not be allocated or an invalid pointer is specified in pushbutton Id. return_val = ZtQuery (pushbuttonld, qstringArglist, NULL); querystr = (char*)qstringArglist[0].ZtValue;

r r

the following call frees the memory allocated for ZtLABEL_STRING */ in the ZtQuery call. ZtFreeArgList(qstringArglist);

Save and Retrieve Objects The ZtSave function allows users to save objects in a file.

List 1

List 2

G HE H

Fig. 4. Cloning lists of objects nonrecursively.

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A filename can be specified by the user in the function Arglist. If the file exists, the user also has the option to overwrite the existing file. Objects or defaults of one appli cation can be retrieved easily in another application with the ZtRestore call. In the following example the window windowld is saved into a file named windfile.w.

/ redraw all objects whether or not they have been modified ZtDo(systemld, ZtREDRAW, NULL); /

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ZtDo(windowld, ZtUPDATE, NULL); /

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ZtDo(pushbuttonld,ZtFLASH, NULL); /

f l a s h

t h e

o b j e c t s

int returruval;

ZtDo(listld,ZtFLASH, NULL);

Ztld windowld

/ erase a rectangle object

/ filename arglist */

ZtDo(rectangleld, ZtERASE, NULL);

static ZtArgListltem saveArglist[ ] =

/

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ZtDo(listld, ZtERASE, NULL); ZtFILENAME,

(ZtValueType)"windfile.w",

/ draw a text object whether or not it has been modified */

ZtOVERWRITE,

(ZtValueType)TRUE,

ZtDo(textld, ZtDRAW, NULL);

NULL,

(ZtValueType)NULL

/ draw a list of objects other than low-level objects */ ZtDo(listld, ZtDRAW, NULL); /

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ZtDo(windowld, ZtRAISE, NULL); /

returruval = ZtSave (windowld, saveArglist)

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ZtDofwindowld, ZtLOWER, NULL);

Locate Objects The capability of locating the closest object near a userdefined point in a window is provided by the function ZtFindByLocation. Users can control the aperture of the search (i.e., how close or how far from the point) and the depth of the search (i.e., whether or not the action should be recursively applied down to primitive objects within any model or composite object]. For example, a row-column object contains a pushbutton object, a text object, and a scrollbar object. A mouse click (i.e., a button event) gener ated on the pushbutton will cause ZtFindByLocation to return the Ztld of the pushbutton if the function Arglist contains the value TRUE for the ZtRECURSIVE attribute. If ZtRECURSIVE is set to FALSE, the return value of ZtFindByLocation will be the Ztld of the row-column object instead of the pushbutton (see Fig. 5). ZtFindByAttribute also enables the user to match objects that have certain properties. For example, if an application creates a large number of objects and some of them are invisible, to find all the invisible objects, the ZtFindByAttribute function is used on the window object, passing an object Arglist with the ZtVISIBLE attribute set to FALSE. Receive Input Functions Input events like button and key presses can be collected using the function ZtDo(Objectld, ZtlNPUT, NULL). Where objectId is the Ztld of a system object and ZtlNPUT is the action for ZtDo to do. The input-handling ZtDo function retrieves the events and dispatches them to the appropriate callback function so that the user-defined action can be executed. User input can be collected continuously or in a single pass. Visual Update Functions In addition to getting input, ZtDo provides several other actions. It provides the capabilities to update, draw, re draw, flash, erase, raise, and lower objects on the display. The following is a list of the different operations possible with the ZtDo function.

Two modes of updating or drawing objects on the display are possible: immediate update and deferred update. In immediate update mode the windows are redrawn anytime there is a visual change in the objects. In the deferred mode, the process of redrawing windows can be postponed until an explicit update is performed through ZtDo(... ZtUPDATE...), or a change in the update mode. This mode is useful if changes need to be made to many objects and it is only necessary to refresh the window once. Both modes are activated by setting the system object's update attribute to either immediate or deferred. The following code puts the system object in the deferred update mode. / update mode arglist for system object */ static ZtArgListltem updateModeArglist [ ] = { ZtDEFER_UPDATE,(ZtValueType)TRUE, N U L L ,

( Z t V a l u e T y p e ) N U L L

}; Ztld systemld, windowld; int return_val;

Mouse Event (rowcolumnld)

(pushbuttonld)

( t e x t l d )

( s c r o l l b a r l d )

ZtRECURSIVE

Ztld Returned from ZtFindByLocation

FALSE TRUE

rowcolumnld pushbuttonld

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Fig. 5. Locating an object with ZtFindByLocation. When a mouse event happens overthe pushbutton, if the ZtRECURSIVE attribute is FALSE the identifier for the row-column object (rowcoiumnid,) is returned. If the ZtRECURSIVE attribute is TRUE, the function searches for the primitive object in the area and returns the identifier for the pushbutton (pushbutton idj.

at some point in the application, set update mode to deferred retum_val = ZtChange (systemld. updateModeArglist, NULL);

* now it is necessary to redraw one of the windows * retum_val = ZtDo (windowld, ZtUPDATE, NULL);

List Manipulation Functions The API list manipulation functions allow programmers to create and manipulate lists of objects. Creating an Object List. The following example creates a list of two points using the function ZtCreateList (see Fig. 6). / arglist for point object */ static REAL64 x, y; static ZtArgListltem pointArglist[ ] =

in a list. Extraction. An object can be extracted from a list of objects by invoking ZtGetListObject and specifying the index of the object, or by using the function ZtGetListTail to extract the last object in a list. Insertion. Objects can be inserted into a list by using: • ZtlnsertListlndex to place the object at a specified index • ZtlnsertListObject to place the object before an object with a known identifier • ZtlnsertListTail to place the object at the end of a list. These functions can be used to add an object to the child lists of windows, models, or composite objects. The follow ing code fragments demonstrate using these functions. Figs. 7a and 7b show the results of the ZtlnsertListlndex and the ZtlnsertListObject examples respectively. / insert an object at location two in list pointListld ' Ztld pointListld, pointi Id, newpointListld, insertpointld, refpointld, pointld; int ret;

{ ZtX, (ZtValueType)&x; ZtY, (ZtValueType)&y, NULL, (ZtValueType)NULL }; / Identifiers for pointer objects */ Ztld pointi Id, point2ld, pointjist; /'Identifiers for pointer objects */ / create a point at (50.0,50.0) */ x = 50.0, y = 50.0; point! Id = ZtCreate (ZtPOINTJDBJ, pointArglist, NULL); / create another point at (60.0,50.0) */ x = 60.0; point2ld = ZtCreate (ZtPOINTJDBJ, pointArglist, NULL); / create the list for these two points */ pointjist = ZtCreateList (ZtLIST_OBJ, pointi Id, point2ld, NULL);

Freeing a List. When the list of objects is no longer needed, it can be freed. The application has the option to free the list along with all the objects it references, or to free the list but retain the objects.

/ / / / / /

pointListld : the Ztld of a ZtLISTJDBJ to insert the object into */ pointi Id : the Ztld of the object to insert into the list newpointListld: the Ztld of the new list. If the function fails, the original pointListld is returned in newpointListld. If the function succeeds, */ the new list is returned in newpointListld. objlndex = 2; ret = ZtlnsertListlndex(pointListld, objlndex, pointi Id, ¿newpointListld);

/ insert an object (insertpointld) into a list (pointListld) */ / in front of another object (refpointld) ret = ZtlnsertListObject(pointListld, refpointld, insertpointld, & newpointListld);

/ free the point list (pointjist) in the example above ' int return_val; static ZtArgListltem recursiveArglist [ ] = ZtRECURSIVE, NULL,

(ZtValueType)TRUE, (ZtValueType)NULL

/ add a point object (pointld) to the end of a point list / (pointListld) ret = ZtlnsertListTail(pointListld, pointld, &newpointüstld);

/ free the list and its references, the two point objects */ recursiveArglist[0].ZtValue = (ZtValueType)TRUE; return_val = ZtFree(point_list, recursiveArglist);

Merging Lists. A list of objects can be merged into another

pointi Id

/* free the list but leave the two point objects alone */ recursiveArglist[0].ZtValue = (ZtValueType)FALSE; return_val = ZtFree(point_list, recursiveArglist);

Bookeeping. Three API functions are provided for retriev ing information about list objects. These functions include: • ZtCheckListObject for verifying the presence or absence of an object in a list. • ZtCountList for counting the number of objects in a list. • ZtGetListlndex for determining the position of an object

point_list

Fig. 6. Data organization illustrating a list of two points created with the function ZtCreateList.

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list by using: • ZtMergeListlndex to place the list at a specified index • ZtMergeListObject to place the list before an object with a known identifier • ZtMergeListTail to place the list at the end of a list. In the following example three objects of type ZtLISTjDBJ are used to illustrate merging lists. Listld references three objects (objecti Id, object2ld, object3ld), Mergeld references two objects (objected and objectSId), and Newlistld is the list object obtained by merging Listld and Mergeld (see Fig. 8). / Using ZtMergeListlndex to insert all objects of Mergeld */ / into Listld between objecti Id and object2ld */ Ztld Listld, Mergeld, Newlistld; int ret_val;

Removing Lists. Objects can be removed from a list by using: • ZtRemoveListlndex to remove an object at a specified index • ZtRemoveListObject to remove an object before an object with a known identifier • ZtRemoveListTail to remove an object at the end of a list. Children of windows, models, or composite objects can be deleted by invoking these functions on the list object specified in the ZtCHILDJJST attribute. Replacement. An object can replace another object using: • ZtReplaceListlndex to place the object at a specified index • ZtReplaceListObject to place the object before an object with a known identifier • ZtReplaceListTail to place the object at the end of a list.

INT32 lisUindex = 1 ; / replace a point object at the index position of a point / list (pointListld) with a new point object (newpointID)

ret_val = ZtMergeListlndexfListld, lisUndex, Mergeld, &Newlistld); / Using ZtMergeListObject to insert all objects of Mergeld into */

/ pointListld : the Ztld of a ZtLIST_OBJ to replace the

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/ newpointld : the Ztld of the object to replace the indexed */ object with

Ztld Listld, Mergeld, Newlistld, object2ld; int ret_val; reLval = ZtMergeListObject(Listld, object2ld, Mergeld,

/ replacedld : the Ztld of the replaced object. This variable may be given as NULL if this return value is

SNewlistld);

n o t

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* /

pointListld

¡nsertpointld

(b)

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Fig. 7. (a) Inserting the object pointld in the list pointListld at index 2. (b) Inserting the object ¡nsert pointld into the list pointListld in front of the object refpointld.

Creating Composites with ztCHlLDJJST

Ztld pointListld, replacedld, newpomtld: INT32 objlndex = 2: int rel: ret = ZtReplaceListlndexfpointüstld, objlndex. newpointld, &replacedld): / The */ code fragment illustrates using ZtReplaceüstObject */ / The object identifiers have the following meanings: ' pointListld : same as above / pointjndexjd: the Ztld of the object to replace * newpointld : the Ztld of the object to replace pointjndexjd */ / replacedld : same as above ret = ZtReplaceListObject(pointListld, pointjndexjd, newpointld, replacedld); / replace the tail object of a point list (pointListld) / with a new point object (newpointld) ret = ZtReplaceListTail(pointListld, newpointld, Sreplacedld);

Grouping and Reparenting Objects Using the methods and techniques described so far, ob jects can be created and grouped together to form an object hierarchy like the one shown in Fig. 1 . This is accomplished using model objects or composite objects. Model objects allow an application to group together composite objects, primitive objects, and other model objects into one group. They are invisible container objects and they do not own any visual attributes. Composite objects have visual attri butes and they make it possible to group together primitive widget objects and other composite objects. Examples of composite objects include menus, menu panes, row-col umns, and scroll lists. There are two ways of creating model or composite objects in API: creating objects with the child list attribute (ZtCHILDJJST), or assigning a group of objects to another parent.

Using ZtCHILDJJST, model and composite objects and their descendants can be created either top down or bottom up. Top Down. The composite object is created with NULL as signed to the child list attribute ZtCHILDJJST. It then be comes the current composite object and all newly created primitive objects will automatically become the compos ite's children. For example, to create a menu system from the top to the bottom, start from the top of the menu hierar chy and work down creating children. This process is sum marized in the following steps: • Create the menu object ZtMENlLOBJ with the ZtCHILDJJST attribute set to NULL. This will make the menu the current composite object. • Create a menu pane object ZtMENUPANEjDBJ. This will make the menu pane a child of the menu object and also make it the current composite object. • Create the menu button objects. This will make the menu buttons children of the menu pane. • Change the attribute ZtCURRENT_COMPOSITE on the sys tem object (ZtSYSTEMJDBJ) to the menu object created in the first step. This will make the menu the parent of the next menu pane. • Repeat the last three steps until all the menu panes and menu buttons are created. Bottom Up. To create a composite object from the bottom up, create all primitive objects, put them in a list, and then create the composite object setting the ZtCHILDJJST attribute to the Ztld of the object list. For example, to create a menu system from the bottom up, start from the bottom of the menu object hierarchy, making the newly created objects children of objects higher in the menu hierarchy. This pro cess is summarized in the following steps. • Create a group of menu buttons and put them in a list object ZtLIST_OBJ. • Create a menu pane with the ZtCHILDJJST attribute set to the Ztld of the ZtLISTJDBJ created in the first step.

Mergeld

-HE -HE -Il :• objecti Id

objected

objectSId

E HE H

Newiistld

>^m *mm

>•• >^· objecti Id

objected

objectSId

objeettld

objecl3ld

Fig. 8. Merging lists. The objects on list Mergeld are merged be tween the first and second objects of list Listid resulting in a new list Newiistld.

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• Repeat the first two steps until all the menu panes and menu buttons are created. • Put all the menu panes into a list object. • Create the menu object with the ZtCHILDJJST attribute set to the newly created ZtLIST_OBJ from the previous step. Reparenting

In API it is not necessary to destroy all the objects created and start all over when the user wants to change the objects' relationships. Regrouping objects by changing relation ships is called reparenting. The ZtChange function makes the task of regrouping very easy. The new child list is simply passed to the desired parent object, and the API takes care of removing the targeted children from the old parent's child list and assigning them to the new parent. For example, the following code segment moves the pushbutton object PushButton 1 from Model 2 to Model 1 , and inserts PushButton 1 into the child list of Model 1. Ztldpblld; Ztld model! Id; Ztldchildlistlld; INT32 ret;

/ / / /

PushButton 1 Id */ Model 1 1d */ Model 1 childlist */ Return Value */

Freeing Model or Composite Objects

The counterpart of cloning model and composite objects recursively or nonrecursively is the ability to free these objects from the intermediate parent. Take the case of an application in which one of its model objects has a rowcolumn object as one of its children. Suppose the applica tion requires that the row-column object be freed, but the children of the row-column object must remain. The API provides an option in the ZtFree function that allows the user to accomplish this task. Setting the ZtRECURSIVE attri bute in the function Arglist to FALSE, and calling ZtFree on the row-column object, destroys the row-column object, and its children become the children of the model object. In contrast, passing a function Arglist to ZtFree with ZtRECUR SIVE set to TRUE will free the row-column object and its children. Symbols and Models

Models can be created as children of other models. A model within another model is called a submodel. For example, in Fig. 1, Model 21 is a submodel of Model 12. The user can create a symbol library out of submodels. Cus tomized sets of commonly used symbols can be created, saved, and reused as submodels. Conclusion

static ZtArgListltem childlistArglist [ ] =

ZtCHILD_LIST, (ZtValueType)NULL, NULL, (ZtValueType)NULL

/* get the current childlist of Model 1 ret = ZtQuery (modeli Id, childlistArglist, NULL); if (ret) { childlistlld = (Ztld) childlistArglist[0].ZtValue;

Based on an object-oriented framework, the API consists of a simplified yet powerful set of functions for creating and activating user interface components. The application developer can learn to use these routines within a short time. The developer is also able to combine the dynamic animation capabilities of graphics and the flexibility and interactive capabilities of widgets to enhance user inter faces for process control applications. Models of physical objects such as machinery and instrumentation can be created to provide context-specific information that the end user can react to more quickly than with a standard terminal-oriented interface.

/ add pushbutton pb1 Id to the end of the childlist of model 1 */ ret = ZtlnsertListTail (childlistlld, pblld, &childlist1ld); if (ret) / Change modeli Id's childlist to include the pushbutton pblld */ / The API automatically updates the childlist of model 2 7 ret = ZtChange (model! Id, childlistArglist, NULL);

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HP IVI Application Program Interface Design To provide the features available in HP IVI, the internal design and implementation of the application program interface leveraged concepts and software from graphics packages, window technology, widgets, Xt Intrinsics, and object-oriented design. by Pamela W. Munsch, Warren I. Otsuka, and Gary D. Thomsen

ONE OF THE MAIN goals of the HP Interactive Vis ual Interface (HP IVI) project was to leverage fea tures from current user interface and software de sign technologies and blend the best of each into the feature set and design of the application program interface (API) functions. In doing so, the project team investigated win dowing, graphics, the X toolkit (Xt Intrinsics), widgets, and object-oriented design. This article discusses the features used from each of these technologies, and how these fea tures are incorporated into the internal design and im plementation of the API functions (see Fig. 1). Windowing

To hide the complexities of the X Window System1'2 from HP IVI application developers, the API provides a layer of simplifying software over X. The only X features left exposed are those that we thought the application de veloper must have access to, or that cannot be layered over. Even with this layer of software, the user still has access to X functions. For example, X provides an event called ConfigureNotify that tells the application that a window has been resized, moved, or changed in some way. The API handles resizing the window object when this event occurs but lets the application decide if all the objects in the win dow should be resized to match the new window's size, or if the objects should maintain their sizes and only the coordinate system of the window should be adjusted. The user still has direct access to the X functions if they are needed. The API also ensures that all X events (e.g., a mouse button press and release) that occur in a window object are sent to the application. This is done through callback techniques based on the Xt callback mechanism. There are also mechanisms and data structures to provide a linkage between X event data formats and API data formats.

features as offered by Starbase. Graphics packages provide coordinate systems that: • Communicate with a particular device (device coordi nates) • Provide display resolution independence (normalized or virtual device coordinates) • Allow the user to work in a system that reflects their world (world coordinates) • Allow users to move, scale, or rotate images easily with out recalculating the placement and size of the image (modeling transformations). Device coordinates (DCs) are the coordinates used to write to a device. For the X Window System, device coor dinates are defined in pixels. Virtual device or normalized device coordinates (NDCs) provide a means to gain independence from the resolution of the display. This coordinate system maps the width and height of a display to the coordinate range from 0.0 to 1.0. Normalized device coordinates define a viewport. A view port is a rectangular drawing region on the display surface. Specifying the viewport in NDCs maintains the ratio be tween the drawing area and the display size regardless of the display resolution. World coordinates provide a user-defined coordinate system. This system allows users to create pictures using the most appropriate coordinate system for the task. For example, if the world coordinates represent the physical dimensions of a factory, using the dimensions from a blue print of the factory to create a picture is straightforward. World coordinates define which area of the unbounded

Graphics

Most graphics packages, such as Hewlett-Packard's Starbase graphics package,3 provide coordinate systems that allow users to write device independent graphics programs. Since creating a user interface with the X Window System is currently done using pixels, the API project team decided to provide API functions that enable user-interface design ers the same type of device independent coordinate system

User Application API Functions API Internal Technologies • Graphics • Windows • Widgets • Xt Intrinsics • Object-Oriented Design

Fig. 1 . The software technologies incorporated into the inter nal design and implementation of the HP IVI application pro gram interface (API).

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world coordinate space is visible in the viewport. This type of coordinate system also provides viewport-size indepen dence and display-resolution independence since the world coordinates remain the same regardless of the phys ical size or resolution of the display. Modeling transformations allow the user to define a slightly different view of the world coordinates for each piece of the picture. Modeling transformations are geomet ric transformations such as scaling, rotation, and transla tion (movement). This feature allows the user to draw an object and then reuse it in the picture by moving, scaling, and rotating it to fit the requirements of the picture. These three coordinate systems and the modeling trans formations are linked together when an object is drawn. First, the object is transformed by its modeling transforma tions to the desired orientation in the world coordinate system. The world coordinates are scaled and translated to fit into the viewport and converted to normalized device coordinates. Finally the normalized device coordinates are converted to device coordinates to draw the picture in the viewport. These transformations are shown in Fig. 2. Widgets and Xt Intrinsics

The widgets (pushbuttons, scrollbars, etc.) and the Xt Intrinsics provide the basis for the API input model and for other API features. The API project team took the input loop from Xt Intrinsics and added processing to handle API graphics objects. Also leveraged from the Xt Intrinsics are the methods for getting file descriptor input and time outs. An extension of the Xt callback technique allows users to attach functions to window objects to handle X events and to API graphic objects, which include geometric figures such as circles, arcs, and rectangles, to handle mouse button events. To keep the number of API functions low, API parameter handling is patterned after Xt Intrinsic Arglists. The API Arglists are arrays of attribute and value pairs. This feature frees the application from having fixed parameter lists that force it to make many calls. The application also doesn't have to pass unnecessary parameters. Parameters that it doesn't pass are automatically defaulted. One deviation from the Xt Intrinsic Arglist is that the API uses a null-termi nated list instead of a counted list. The API also extends

Modeling Transformations • Scaling • Translation • Rotation

WC to NDC Transformation

World Coordinate (WC) System (meters.grams, inches, etc.)

XtMainLoop

XtNextEvent (& event)

XtDispatchEvent (& event)

Get Next X Event (e.g., button press)

Call Event Processing Function

Fig. 3. The Xt Intrinsics XtMainLoop function.

the attribute default concept so that the application can change the defaults of different classes of objects at run time. API Arglists are described in the article on page 11. Object-Oriented Design

HP IVI is an object-oriented system. Object-oriented de sign and object-oriented programming are being increas ingly used at HP for software product development.4'5 The goals of object-oriented methods are very appealing be cause they encourage such practices as code reuse and functional cohesion of software components (objects). Also, once a stable and reliable library of objects is avail able, software development and maintenance costs should be reduced. In the API a special utility was used to create an object-oriented environment from C language programs. The box on page 29 describes some basic object-oriented concepts and an overview of the API object-oriented envi ronment. The special utility used for creating the objectoriented environment is described later in this article.

Input Handling The input handling model for the API is based on X, Xt Intrinsics, and widgets. The Xt Intrinsics provide a way to call application functions when certain events occur. These functions are called callbacks and are attached to widgets. The Xt Intrinsics provide input handling capabilities for X events, time-outs, and file descriptor input through the XtMainLoop function. This function consists of an infinite loop calling XtNextEventQ to get the next event and XtDispatchEvent() to send the event to the appropriate processing function (see Fig. 3). Because the API provides several spe-

NDC to DC Transformation

Normalized Device Coordinate (NDC) System 0,0

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Device Coordinate (DC) System (in Pixels) 1023,767

Fig. 2. The coordinate systems and the transformations involved in transforming an object from world coordinates to device coor dinates.

cial input features the project team implemented its own version of XtMainLoop. The basic API input loop consists of an HP-UX selecto call to see if input exists on either the user's file descriptors or the API server object's file descriptors and a test to see what events came in (see Fig. 4). If input is pending on the file descriptor for the X server a message is sent to the API server object to process all X events queued. If input is pending on a user's file descriptor the user's callback func tion is invoked. The server object still does the XtNextEvent() and XtDispatchEvent() looping but it has additional code to handle conversion of X callback information to API format, callbacks on graphic objects and window objects, Expose and ConfigureNotify events on window objects, global callbacks, and event grabbing (see Fig. 5). Callback Handling

callbacks eliminates having one attribute per callback for each object type and eliminates having to add and delete attributes when reasons change. Time-outs and file de scriptor callbacks are attached to the API system object, which stores global attributes and resources. X event callbacks are registered on the window objects. The API creates an identifier (Ztld) for each object that an application creates. However, the data returned to callbacks from a widget consists of a widget identifier and widget-specific data, which is unusable to API applica tions. This problem is solved by minifunctions that are registered with the widgets. These minifunctions are inter faces that convert widget-specific data into something that can be understood and used by the API. When a minifunction is attached to a widget, the object identifier Ztld is also attached to the widget. This scheme allows widgets to be treated like other API objects when widget input is re ceived.

Callbacks are implemented as objects in the API. These objects contain a pointer to the user-written function to be called when an X event occurs, a pointer to callback-spe cific data, and the specific reason that will cause the callback to invoke the user function (see Fig. 6). The file descriptor that is checked during input processing is an example of callback-specific data. The reason for the invo cation of the callback is an integer value that indicates the type of input event such as a button press. These callback objects are put in a list called a callback list and are attached to the object requiring them. For the Xt Intrinsics, the callbacks are attached to specific-reason resources instead of one central callback list. The API method of handling

Get Next X Event (XtNextEvent)

Scan for Input File Descriptors (select ( ))

Dispatch Event to Xt Intrinsic XtDispatchlnput ( )

Events Pending

Input on User File Descriptor

Yes

handle_event Message to Server Object (Fig. 5)

Call User File Descriptor Callback

No

Fig. 5. The API server object event handling loop.

Fig. 4. The API input loop.

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Callbacks on Graphics

Graphic objects include shapes such as arcs, rectangles, and circles. Because graphic objects can be manipulated the same as windows and widgets in the HP IVI environ ment, we decided to have button press and button release events associated with them. Therefore, graphic objects need callback functions. For example, an octagon-shaped graphic object representing a stop sign may require a callback object with a method for stopping some operation. Callbacks on graphic objects are handled differently from widgets. Since the graphic objects are not widgets, the Xt Intrinsics cannot be relied on to call API functions when an event occurs on a graphic object. All widget and graphic objects have a corresponding extent object. The extent ob ject consists of two point objects that define a rectangular region. When associated with an object, the extent defines the smallest rectangle that encloses an object (see Fig. 7). When the minifunction for window events detects a button press or button release, it converts the x,y coordinate posi tion of the sprite to a point object. Since the window minifunction is called, this indicates that the button event did not occur over a widget (remember the widget minifunction converts widget data to API usable data). The button event results in a call to a function to find the object that is under the point. The function will search the hierar chy for an object that has the point in its extent. If a graphic object is found, the object list is searched to see if there is a corresponding callback function and if so, the event is dispatched to the function. Global Callbacks

A requirement of the API was to detect a function key press regardless of the location of the sprite in the window. This was a problem if the sprite was over a widget when a function key was pressed because widgets grab any input over them. The project team extended the callback process so that the window object could also receive the event even if it was over a widget. This type of callback is referred to as a global callback. Global callbacks are implemented by providing an addi tional check during the input processing in the server object (see Fig. 5). After the event is dispatched to the appropriate object, a check is made to see if global callbacks are enabled. Callback Object

If so, the event is dispatched again to the window object and any global callbacks attached to the window that match the event are called. For events that were originally over widgets, the x,y coordinates of the event are recalculated to be relative to the API window object before dispatching. Recalculation of widget points is done because the API understands points relative to the window object coordi nate system and not to the widget coordinate system. Event Grabbing

For customers making their own user-interface builders and also for HP IVIBuild, a feature was needed to direct events only to the window. For example, the normal be havior for a widget pushbutton object is to flash when it is selected. However, in the builder, selecting the push button may be the start of a move operation on it. To sup press normal widget behavior and let the application deter mine the meaning of the event, a button press event over a widget has to be directed only to the window object. The event has to be grabbed. To solve this problem, input han dling at the server object level was modified so that if event grabbing is enabled, the event is only sent to the window object for processing. Window Expose and Resize

When Expose and ConfigureNotify events occur on API win dow or graphics objects, special functions are called in the server object to handle these events. Since graphic objects are not in individual X windows as the widgets are (see Fig. 8), the window object has to redraw the graphic objects when an Expose event occurs and resize its children when a ConfigureNotify event occurs. For an Expose event, the window object removes all Expose events for this window from the queue and keeps two lists of corresponding extent objects. Remember that an extent object consists of two point objects that define a rectangular Graphic Object (a Circle)

Window

(a) User Written Function

Method for Drawing a Circle

Point Objects

Reason for Callback (Integer Value Representing Type of Callback)

(b) Callback-Specific Data (e.g., File Descriptors)

Fig. 6. A callback object in the API.

Fig. 7. An API graphic object with an extent for defining the smallest rectangle around a graphic object, (a) The graphic object (a circle) in a window and the extent represented by P1 and P2. (b) internal representation of the graphic object.

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region. One list contains the extents of each Expose event in device coordinates. This list is used in the server object to create X clip rectangles when graphics objects in the exposed region are redrawn. The second list contains ex tents of each expose event in normalized device coordi nates. After constructing these two lists, the window object goes through a redraw pass of the objects in the window. When the graphics objects are told to display themselves, they check the previous normalized device coordinate clip list to see if they are in the exposed areas. If they are, they send a message to the server object to do the X drawing commands. This scheme ensures that only those objects that are actually exposed get redrawn by the server object and it significantly improves performance if exposed ob jects are only a small portion of the window. For ConfigureNotity events, the window object sets the new window placement and size values. Then during the next redraw of the window, the objects are redrawn to fit within the new window size.

Coordinate Systems The coordinate system concepts and techniques found in various graphics packages are incorporated into the API functions for drawing graphics objects, windows, and widgets on the display. The user can define the viewing area in world coordinates (e.g., inches, feet, etc.) and the API functions transform these coordinates to a window in the X coordinate system pixels. A viewport is a rectangular portion of the display onto which window objects defined in world coordinates are mapped. Viewports are typically defined in a device inde pendent coordinate system called normalized device coor dinates, or NDCs. In X a viewport is represented by an X window, which is defined in device coordinates (DCs). The API allows users to define the position and size of a window object (viewport) with NDC coordinates. This allows a win dow to be defined as occupying a certain portion of the total display area independent of display resolution. Map ping a window object described in NDCs to the device coordinates of a display is straightforward. When an appli cation initiates drawing to a specific X server, the display resolution of the server is queried. The NDC values describ ing the viewport are multiplied by this display resolution

to get pixel values. Since NDCs use the lower-left corner of the display as the origin and X uses the upper-left corner as the origin, the y values of the viewport must be sub tracted from the height of the display for compatibility with the X coordinate system. Since this calculation is done at run time, the application does not need to know the type of display the application is using. Consider a window that occupies the NDC region from (0.0,0.0) to (0.5,0.5) on a display that is 1024 pixels wide and 768 pixels high (see Fig. 9a). When converted to DCs as explained above, the window occupies the region of the display at pixel locations (0,767) to (511,384) (see Fig 9b). The transformation equations for converting from NDCs to DCs are: PXDC = PXNDC x (width of display in DCs/1 NDC) (1) PyDC = PyNDC x (height of display in DCs/1 NDC). (2) To take into consideration the upper-left origin of the X Window System: P'yDC = height of display in DCs - PyDc-

Substituting the values from Fig. 9a into equations 1 and 3 and compensating for the starting pixel yields:

1.0,1.0

Display Resolution

oox~ Origin

Window Object

Graphic Objects

(3)

Widgets

J = Widget Window

(1023,767)

Fig. 8. Widgets are in their own individual windows and have their coordinates defined relative to these individual windows. Graphic objects have their coordinates defined relative to the window object they are located in.

Fig. 9. (a) Window defined in normalized device coordinates (NDCs). (b) The same window defined in device coordinates (DCs) in the X Window System.

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PIXDC = 0-0 x 1024/1 = O PJyDC = 768 - (0.5 X 768/1) = 384 P2xoc = (0.5 X 1024/1) - 1 = 511 = 768 - (0.0 X 768/1) -1 = 767.

These coordinate values are shown in Fig. 9b. To define what is drawn within the window object, the user defines what portion of the world coordinate (WC)

space is viewable in that area. This viewable area can be changed at run time to perform operations such as panning or zooming. To draw to the X window representing the user's window object, the API must convert all values in WCs into the device coordinates of the display. WCs are transformed to pixels in a two-step process. The first step transforms the WCs to NDCs and the second step transforms the NDCs to DCs. Viewable Area in WCs ( 1 0 . 0 , 8 5 . 0 )

Display

(0.5.1.0)

( 1 1 0 . 0 , 8 5 . 0 )

(1.0,1.0)

Viewport for Window Defined in NDCs (1.0,0.5)

(0.5,0.5)

(10.0,10.0) (60.0,10.0) (110.0,10.0)

(a)

Window

Window

Window

(0.0,0.25) (0.25,0.25) NDC Origin

Pushbutton

(0.05,0.067) (0.3,0.067) (b)

( 0 . 0 , 0 . 0 ) (

c

( 0 . 2 5 , 0 . 0 )

)

D i s p l a y

( ( 0 0 )

( 0 . 0 , 0 . 5 ) d

( 0 . 2 5 , 0 . 5 )

)

W i n d o w

(0,192) (255,192)

384 Pixels

(0,383) 512 Pixels

Fig. defined (a) The viewable area of the world coordinate window is defined to occupy the upper-right quadrant of the display, (b) Results of applying the x and y scale factors to the pushbutton coordinates, (c) Results of applying translation factors to the scaled pushbutton coordinates, (d) Results after applying the flip factor tc compensate for the X window origin in the upper-left comer of the NDC space, (e) Results after transforming the pushbutton from NDCs to DCs.

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Every window object contains a viewport-to-window transformation matrix (VTM). This matrix describes how to scale and translate the viewable WC region to fit within the window. A scale factor (SF) is calculated to scale the WC width and height to the width and height of the view port. This scale factor for the x coordinate is:

For the pushbutton example the translation factors are: Tx = - 0.005 x 10 = - 0.05 NDCs Ty = - 0.0067 x 10 = - 0.067 NDCs. Adding the translation factor to the NDC points P! and P2 results in:

SFX = width of the window in NDCs^-width of the viewable WC region in WCs

Plx = 0.05 - 0.05 = 0 NDCs P2x = 0.3 - 0.05 =0.25 NDCs

and for the y coordinate is Ply = 0.067 - 0.067 = 0 NDCs Pzy = 0.318 - 0.067 = 0.25 NDCs.

SFy = height of the window in NDCsn-height of the viewable WC region in WCs. For example, in Fig. 10a the viewable coordinate window is defined to occupy upper-right quadrant of a display. The mapping the WC region to NDCs in this

area of the world a viewport in the scale factors for example are:

SFX = (1 - 0.5)/(110 - 10) = 0.005 NDCs/WC and for the y coordinate SFy = (1 - 0.5)/(85 - 10) = 0.0067 NDCs/WC

Fig. lOc shows the results of the translation. Like most graphics packages, the API follows the conven tion of defining the origin in the lower-left corner of the drawing area. However, because the X Window System defines the origin to be the upper-left corner, an additional translation factor (or flip factor) must be added in the y direction to move the origin from the lower-left to the upper-left corner. The NDC height for the window in which the pushbutton in Fig. 10 resides is 0.5 NDCs. Compensating for the flip factor (F) results in: P ' iy= F - P , v•2y = 0.5 - 0.25 = 0.25 NDCs = 0.5 - 0.0 = 0.5 NDCs â € ” F - P l y

To transform the pushbutton coordinates shown in Fig. 10a from WCs to NDCs:

P ' 2 y

and

Plx = 10 x SFX = 0.05 NDCs P2x = 60 x SFX = 0.3 NDCs

P'ix = 0.0 P'2x = 0.25.

Ply = 10 x SFy = 0.067 NDCs P2y = 47.5 x SFy = 0.318 NDCs. Fig. lOb shows the pushbutton scaled to NDC coordinates. The NDC system maps the coordinate (0.0,0.0) to the lower-left corner of a window. Therefore, if the viewable WC region does not map the coordinate (0.0,0.0) to the lower-left corner of the window, a translation factor is added to the NDC coordinates. The translation factors are computed as:

Fig. lOd shows the result of applying the flip factor. The scale factors, the translation factors, and the flip factor are incorporated into the viewport-to-window trans formation matrix VTM. Combining all the transformation factors in one matrix and performing the transformation operations looks like:

Tx = - SFX x (WCX origin) Tv = - SFV x (WCV origin)

API Functions (Interface to User Code) API Object Layer Original Widget

Device Independent Layer

(Process Attributes and Update Objects) Server Object

•Hi

Widget Scaled Larger

(Interface to X, Xt Intrinsics, and" Widgets)

Widget Scaled Smaller

Widgets Xt Intrinsics X Window System

Fig. 1 1 . The effects of scaling widgets larger and smaller around characters.

Device Dependent Layer

Fig. 12. The layers of the API architecture.

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[P

xNDC yNDC

~

[ ? x W C

P y W C

SFX O O - SFV Tx (-T, + F)

Fig. lOe shows the final transformation of the pushbutton NDCs to X window device coordinates. The coordinate points shown in Fig. lOe are derived by substituting the values from Fig. lOd into transformation equations 1 and 2 and compensating for the starting pixel. PIXDC = 0.0 x 1024/1 = 0 PlyDC = °-25 X 768/1 = 192

P2xDC = (0.25 X 1024/1) -1 = 255 P2yoc = (0-5 x 768/1) - 1 = 383. Modeling Coordinates

The API provides modeling transformations that allow any object within the user interface hierarchy to be trans formed by scaling (enlarging or shrinking), rotation, and translation. This lets the user draw a symbol that can be reused by providing only the data that differentiates its position and size from another instance of the symbol. The API concatenates modeling transformations so that an ob ject is affected by the transformations on its ancestors. This allows an entire subhierarchy of objects to be transformed by one operation ona common ancestor instead of requiring transformations on every object in the subhierarchy. These transformations are used when an object is being drawn. The modeling transformation values are converted to WCs by multiplying the transformation on an object to its WC attributes. A current transformation matrix (CTM) is main tained during a drawing pass on the objects. Each object multiplies its transformation matrix with the CTM contain ing the transformations of its ancestors. In the API, the CTM is initialized to be the VTM. Doing this reduces the number of matrix multiplications and improves the perfor mance of the drawing operation. Adjustments and Scaling

Besides allowing the application developer to work in a display resolution independent manner when creating the windows for an application, the world coordinate system allows a user to resize the window interactively and the objects to be redrawn without the intervention of the appli cation. Changing the size of the window changes the NDC definition of the window. This change causes the scaling factors in the VTM to be recalculated at the next display pass. The objects are either enlarged or shrunk to fit within the new window size. When resizing a window, the user may change its aspect ratio. That is, the physical width-toheight ratio of the object may be different from the WC width-to-height ratio. When this happens, objects begin to look distorted. For instance, a circle begins to look like an oval. This may be an appropriate action for some applica tions, but for others, especially those where the objects on the display are meant to represent something in the phys ical world, the application developer wants the objects to maintain their width-to-height ratio. In graphics packages, these two modes of operation are referred to as anisotropic and isotropic scaling, respectively. The API window object provides the attribute ZtADJUST which the application can

set to ensure that the aspect ratio is maintained. If this attribute is set and the window is resized, the WC height or width mapping to the window is adjusted to maintain the original aspect ratio. This process results in modifying the scale factors stored in the VTM. This also results in more viewable WC space in the window in either the x or the y direction. Applying the various coordinate systems to windows and widgets has worked successfully. Specifying their po sition and size in NDC or WC units allows the user to define them in the same manner as graphic objects. It also allows the application to be independent of the display and window size even as the user interactively resizes the window. Scaling and moving widgets works the same as for graphics objects. However, as the widgets scale smaller and larger, the font that they use does not scale because it is a bit-mapped font. The widget scales larger and leaves more space between the edge of the text and the edge of the widget or it scales smaller and closes in on the text, even tually clipping it (see Fig. 11). A few possible solutions to this problem exist. One solution is for the X Window Sys tem to support scalable fonts. This will allow the font to scale with the widget. Another solution is to switch be tween a set of fonts with different sizes as the object grows and shrinks. Widgets also cannot rotate from a horizontal base. In the API, when a widget is rotated, its defining point is rotated, and the widget is redrawn in the new position with a horizontal base. This allows the widgets to be rotated as part of a symbol and to move along with any associated graphic objects. Despite these differences (continued on page 30) Types of Files:

Class Header File (e.g., circle. h) Class Definition File (e.g., circle. c) Library Definition File (e.g., graphic. r) Run-Time Class Information File (e.g., circle.rtc) Glue File (e.g., classlibs.c) 1. Run rtc on Library Definition File ~^ circle.rtc graphic. r

-> graphic.h" -> graphic.c

2. Compile the Class Definition File circle.c circle.h

circle.o

circle.rtc

3. Compile C Source File graphic.c Generated from rtc Tool

4. Glue Library Definition Object File classlibs.c -

->• classlibs.o

graphic.h

Fig. 13. The process of adding a new object to the API object hierarchy.

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Object-Oriented Design in HP IVI HP IVI is an object-oriented system. It uses a set of facilities called the HP IVI object-oriented environment (OOE) to provide the framework for its implementation. The OOE has two parts: a messaging interface and a tool for compiling an external descrip tion of the class hierarchy into C language code. The C code defines the dispatch tables used by the OOE's interface functions to perform messaging (object communication). Presented here are some basic concepts of object-oriented design and an over view of how the OOE implements some of these concepts. Object-oriented design and programming are proving to be a natural and productive paradigm for software development be cause they enable developers to represent relationships among system components and the tasks to be performed on these components in a more natural manner. The main concepts of this methodology include objects, messaging, polymorphism, and inheritance. Objects. An object is the basic unit in object-oriented methodol ogy. refer is a structure that contains local data structures and refer ences the local procedures (called methods) that operate on the data (see Fig. 1). The current values of an object's internal data define the object's current state. The object's behavior is depen dent on and current state. The data inside an object is private and accessible only through one of the methods associated with the object. An object acts on its data when it receives a request asking one of its methods to perform some operation. This mech anism is called messaging. Objects are created from a template called a class. There can be many objects of each class. These objects are called in stances of the class. Each instance is an independent object with its own data and state. However, an object instance has the same data structures, shares the same methods, and behaves the same way as all other instances of the same class. This means that objects of the same class will respond to the same messages — differences in object behavior depend on the current state (the values of the object instance's data). For example, all object instances of an object class that draws rectangles will respond in the same way to a request to draw a rectangle. How ever, because of differences in the state of the internal data structures, the rectangles may be drawn in different sizes, colors, and positions. The OOE tool mentioned above is called the rtc (run-time class information) tool. The rtc tool compiles a symbolic external rep resentation of the class hierarchy into the data necessary for

defining classes and methods for those classes. The symbolic representation of the class hierarchy is compiled by the rtc tool to produce static tables called dispatch tables which consist of two pieces: a category table and method tables. These tables contain information necessary to dispatch messages to objects. A unique key called the message selector is used tc search the dispatch tables for a pointer to a function that will service a request. The rtc tool also generates a file containing definitions of symbolic names for the constants that represent the message selectors. Coding using the symbolic names for the message selectors provides independence from the structure of the under lying rtc tables and provides more readable code. The rtc tool and the type of files it compiles and generates are described in more detail on page 31 . Messaging. Objects communicate with each other through mes saging. Sending a message to an object requests that object to perform some action — usually the manipulation of its internal data. Messages consist of a minimum of two arguments: the receiver of the message (i.e., the object) and the message selec tor. The message selector consists of a category name and a method name. The object receiving the message looks up the category selector in the category table and then looks up the method in the corresponding method table. This selection mech anism is controlled by a set of central messaging routines. These routines are contained in the message interface to the OOE. Every object contributes a dispatch table that the messaging routines search to determine which object implements a function for a a selector. Associated with each selector is a pointer to a method that is called to implement the response to the message (see Fig. 2). This connection of a message selector to the appropriate method is called binding. Binding can take place at compile time (early or static binding), or at run time (late or dynamic binding). The OOE currently implements static binding. In the OOE, the message selector is the key to determining which function gets called when a message is sent to a particular object. The message selector is a 32-bit quantity consisting of

ObjecLa

Object

Data Private to Object

message (Object.a, selector)

t

Receiver

Fig. the An object. The internal data structure is private to the object and the methods have sole access to the data.

Fig. 2. Connecting a message to a method in an object.

OCTOBER 1990 HEWLETT-PACKARD JOURNAL 29

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message (Object_a, Display_Time)

message (Object_b, Display_Time)

Object_a

Object_b

15:00:25

Fig. 3. regardless allows the same message to be sent to different objects regardless of their internal data types and methods. two 16-bit fields. The upper 16 bits of the selector defines the offset of the category to which that message belongs in the class's category table. The lower 16 bits defines the offset of the method function pointer in the method table. If the value of a particular position in the dispatch table is NULL, the messaging routines traverse up the class hierarchy searching for a method function pointer. When a function pointer is found, it is copied to the position in the dispatch tables where the upward traversal of the class hierarchy began. This tends to improve the performance of the messaging system over time because the amount of upward searching is slowly replaced by direct function calls and the NULL values in the dispatch tables gradually disappear. Also, the implementation of categories im proves memory use by eliminating method tables when a class does not support that category. Polymorphism. The concept of polymorphism in object-oriented programming enables different types of objects to share a com mon operational interface and to be manipulated by user code independent of the actual types of objects. This means that the application program does not have to differentiate the object type at run time. This differentiation is performed automatically by the messaging system. For example, a message to a clock object to display the time would redraw the hands in a particular position if the clock were drawn as an analog clock, while the same message would cause the time to be displayed in text format for a clock drawn as a digital clock (see Fig. 3). The clock object is polymorphic because the same message can be sent to different objects. The application does not have to worry about how the time is drawn. That is determined when the method to draw the clock interprets the instance data that defines each clock is internal state. A goal of object-oriented design is Root Class Class A

to maximize code generality, flexibility, and reusability by defining common interfaces that can be supported by many different kinds of objects. The mechanism of searching the class hierarchy described above is how the OOE implements the concept of polymorphism. Inheritance. Inheritance provides the ability to create incremen tal definitions of objects (i.e., one kind of object can be defined incrementally in terms of previously defined objects). The new definition extends the existing definitions by adding data to the object representation, by adding new methods, and by extending the definition of existing methods. Using the update time example from above, the analog clock object that produces the graphic representation of the time might only implement the method that draws the representation of the clock and inherit the more basic functions (e.g., audible alarms) from the more general digital clock class. Inheritance allows object definitions to be shared (rather than copied) and customized by extension (rather than by modification). A goal of object-oriented design is to organize object definitions so that common behavior is specified in shared definitions and object definitions can be extended. The external representation of the class hierarchy that is pro cessed by the OOE class compiler (rtc tool) builds tables of function pointers. Entries that are not NULL in these tables indicate that a particular class implements a particular method. NULL entries indicate that a particular class inherits a particular method. The class compiler also declares a pointer to the class's parent in the hierarchy (see Fig. 4). The OOE messaging routines use this information to traverse upward in the class hierarchy when searching for a method. In object-oriented systems, classes may have one parent or many. Single inheritance allows a class to have only one parent. This is the model implemented by the OOE. Object-oriented lan guages such as Smalltalk and C++ allow classes to have more than one parent. This is called multiple inheritance.

Class B

Pam Munsch Project Manager Industrial Applications Center Steve Witten Development Engineer Industrial Applications Center

message (classBObj, method_2);

Fig. 4. Inheritance allows methods to be reused.

between the operation of the widgets and the graphic and window objects, the coordinate system feature of the API

still provides a large productivity gain for the application developer.

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Object-Oriented Architecture Without using an object-oriented programming language. the API encompasses features provided by an objectoriented language through conventional C language fea tures. The API's architecture is divided into three layers: the API function layer, the API object layer, and the device dependent layer (see Fig. 12). The API function layer pro vides the communication interface between a user applica tion and the objects created by the application. It is a thin layer of code that validates the user's parameters and sends messages to the objects to perform the tasks requested. The functions provided in this layer are described in the article on page 11. In the API object layer, an object is created and destroyed and all manipulation of an object's data occurs. In the device dependent layer, all the function calls to underlying subsystems are made to draw an object to the display. Messaging in the API

The API consists of a number of function calls that pro vide the communication path between an application and the underlying objects manipulated by the application. Most of the API functions require objects as parameters. It is through this interface that an object's specific data and the functions that manipulate the data are accessed. In essence, the API hides from the user as much as possible the details of using objects. To provide the interface between an application and its objects, a preprocessor tool called rtc (run time class infor mation) is used to define the API object messaging facility and class interitance hierarchy based on information from a group of description files. Every API class consists of a class header file and a class definition file. The class header file defines the data storage for each instance of an object of that class. This file identifies the object as a member of a class or classes and provides the connection to the set of methods that manipulate that object's internal data. The class definition file is a C program module that contains the methods that are specific to a particular class. The class header file must be included in the C program module so that the data structure of this object and the class definition pointer can be accessed. Once an object's data structure, class, and specific functions are defined, it needs to be positioned within the class hierarchy. The positioning of the class in the class hierarchy is determined by the nature of the class and the methods to be inherited. The simpler a class is, the higher up in the class hierarchy it is positioned. Conversely, a more complex class is positioned further down in the class hierarchy. The positioning of a class within the class hierarchy is defined within the library definition file. This file defines the methods that are avail able for messaging to a class and the methods that can be inherited by that class. Adding an API Object

Adding a new class to the API class hierarchy is a fourstep process. This process is illustrated for the circle class in Fig. 13. First, the library definition file (graphic.r) is used as the input to the rtc tool. The rtc tool takes the library definition file and produces several files as output. One of

these output files (circle.rtc in Fig. 13) is the run-time class information file, or .rtc file. A .rtc file is created for every class defined in the library definition file. It contains the class definition structure and the method dispatch tables for that specific class. The .rtc file is included at the end of the class definition file for that class when the class definition file is compiled (step 2). In the third step the new library definition files (graphic.h and graphic.c) are com piled. Finally, the pointer to the new class must be added to the file that defines the class hierarchy. This file is called the glue file (classlibs.c). In step four, classlibs.c is compiled with the class header file (graphic.h) to produce the object file classlibs.o.) When these object files (circle.o, graphic.o, and classlibs.o) are linked into an application, the addresses to the methods supported by the various classes are resolved. By using object-oriented technologies, the API is able to create graphic objects. One problem users have with soft ware systems such as the X library is that graphic primitives are not objects. The X library provides many graphic func tions that operate on the individual pixels of a graphic display but the parameters describing the object are not kept. For example, if a circle is drawn and the application simply wants to change its color from blue to red, all the parameters (location, size, line width, etc.) to draw the circle must be passed to the X library function again. The API solves this problem by providing graphic objects using the rtc tool. This allows the user to describe the parameters of the object once and then make simple modifications only to the parameters that are changing. The application is freed from maintaining all of the data necessary to redraw all of the graphical objects in the window. Conclusion

The HP IVI project was successful in blending graphics, windowing, X toolkit, widget, and object-oriented tech nologies in the internal design of the API. Because most of these technologies were developed separately, it was not always clear how to integrate them. The API solved most of the problems encountered and as a result of this effort a high-level user interface toolkit was created that reduces the complexity of building a sophisticated graphical user interface for an application. Acknowledgments

Besides the three authors, the other members of the API development team were Scott Anderson, Hai-Wen Bienz, Mark Thompson, and Mydung Tran. References 1. F. E. Hall and J. B. Byers, "X: A Window System Standard for Distributed Computing Environments," Hewlett-Packard Journal, October 1988, Vol. 39, no. 5, pp. 46-50. 2. K. H. Bronstein, D. J. Sweetser, and W. R. Yoder, "System Design for Compatibility of a High-Performance Graphics Library and the X Window System," Hewlett-Packard Journal, December 1989, Vol. 40, no. 6, pp. 6-12. 3. Ibid, p. 7. 4. J. A. Dysart, "The NewWave Object Management Facility," Hewlett-Packard Journal, Vol. 40, no. 4, August 1989, pp. 17-23. 5. T. F. Kraemer, "Product Development Using Object-Oriented Software Technology," Hewlett-Packard Journal, Vol. 40, no. 4, August 1989, pp. 87-100.

OCTOBER 1990 HEWLETT-PACKARD JOURNAL 31

© Copr. 1949-1998 Hewlett-Packard Co.

HP IVIBuild: Interactive User Interface Builder for HP IVI Using the facilities provided by HP IVI's application program interface, HP IVIBuild allows developers to create and experiment with different types of application user interfaces, save them in files, and bind them to the functionality of the application at run time. by Steven P. Witten and Hai-Wen L. Bienz THE EDITOR/BUILDER COMPONENT of the HP In teractive Visual Interface product is HP IVIBuild. As its name implies, HP IVIBuild is a tool that is used to build user interfaces interactively. The windows and objects that make up the user interface can be saved in a file and reused later by other applications using the API functions (see Fig. 1). HP IVIBuild is itself an HP IVI appli cation program because it uses the API functions described on page 11 as a platform. Fig. 2 shows the architecture of HPIVIBuild. Early in the design of HP IVIBuild we realized that al though the HPIVI application program interface (API) func tions are several orders of magnitude easier to use than

HP IVIBuildCreated User Interfaces

Xlib, the X toolkit, and widgets, they are still very complex to many users. Therefore, an interactive user interface de sign tool, HP IVIBuild, was developed to complement the API functions. HP IVIBuild helps promote software development pro ductivity in areas such as rapid prototyping and the design and modification of user interfaces. For rapid prototyping, HP IVIBuild allows developers to create complex prototype user interfaces. The user can interactively place and size all of the primitive graphics and widget objects in a win dow. Once the objects are placed and sized, many of their physical attributes such as colors, shadows, strings, and fonts can be changed easily within HP IVIBuild. Even some one who does not have any software background, such as a human factors expert, can use HP IVIBuild to design a

Processing States Display Output

Interstate Transition State Machine • API Functions • HP IVI Object-Oriented Environment

User Input

HP IVI Widgets Graphics Driver xt Intrinsics X Window System

Files Containing f Saved User ( Interfaces L

Applications Restoring User ( Interfaces and Adding Functionality

Workstation To Display Hardware Application

Application

Fig. 1. HP IVIBuild allows users to create and experiment with different user interfaces and save them in files to be reused by other API applications. (API = application program interface of HP IVI.)

Fig. 2. The components that make up the HP IVIBuild ar chitecture.

32 HEWLETT-PACKARD JOURNAL OCTOBER 1990

© Copr. 1949-1998 Hewlett-Packard Co.

complex user interface. This means that an application's user interface can be prototyped and evaluated separately from the operations performed in the application. Besides restoring the user interfaces created with HP IVIBuild, the API functions in the application also make the objects in the interface react to user input. Callback functions, which are invoked in response to user input to the application, can be attached to those objects that should respond to user input. If the application requires changes to the user interface in response to application or customer needs, the previously saved user interface can be modified with HP IVIBuild. If the changes involve adding new ob jects, callbacks can be added to the new objects using the API functions in the application program. However, if changes are made to existing objects, no changes need to be made to the application program. Fig. 3 shows the interface areas provided by HP IVIBuild. The functions of these areas are: • Utility Box. This area displays current object information and the menus for object manipulation. • Tool Box. This is the area in which the user selects the objects to be manipulated. • Workspace. This area displays the windows being created.

concepts of objects, polymorphism, and inheritance are incorporated into the design of HP IVIBuild. Objects. In HP IVIBuild objects are very simple data struc tures called states. A state is the context of user input (i.e., the operation in progress) at any particular point in time. All states are static (bound at compile time) and have the same structure. Only one field in the structure, called a message selector, is filled in at run time. This field is used to bind HP IVIBuild's user interface presentation to its functionality. User interface binding and functionality are discussed later in this article. The following is the C lan guage structure of a typical state object. /• compatibility with the HP I VI ,'* object-oriented environment and */ / is not used by HP IVIBuild. extern struct ClassDef_DzRect;

/ Structure containing pointersto */ / this state's method dispatch / tables. This structure is / created by the API rtctool.

static INT32groupmembership[] { /'Array containing a state's = } ;

Object-Oriented Design in HP IVIBuild

/ This macro is included for

CLASSVARS(ClassVars)

N U L L

/

g r o u p

m e m b e r s h i p

i n f o r m a t i o n .

/ ' T h e p u r p o s e o f t h i s a r r a y i s t o / help limit state transitions

HP IVIBuild uses the API functions and the facilities provided by the HP IVI object-oriented environment to build its own object-oriented system. The object-oriented

/ at certain times. Currently / this feature is not used in /"HP IVIBuild.

dJ. File Edit Selec

O Graphics

Prompt: Select s menu ite« or Tool box button.

Current Model:

Utility Box Tool Box

Workspace Area

Fig. 3. . Interface areas of HP IVIBuild.

OCTOBER 1990 HEWLETT-PACKARD JOURNAL 33

© Copr. 1949-1998 Hewlett-Packard Co.

static char objectname[ ) = "sject"; / this state's name */ / All state objects have the following structure. */ static struct DzRect{ struct ClassDePclass;

/ Pointer to the dispatch tables.

char *statename;

/ Pointer to the state's name.

INT32clsindex;

/ A unique id assigned to this state. */

INTSautoterm;

/ This state's autotermination */ /*flag (if TRUEthestate machine */ / terminates the state and if FALSE */ / an action by the user must */ / terminate the state). */

INT32 selector;

/ Message sent to the current state */

ment state transitions in HP IVIBuild. Polymorphism. HP IVIBuild's central input handling facil ity, which is called the state machine, depends on the concept of polymorphism. All states in HP IVIBuild have the same operational interface (i.e., the state object is polymorphic). Therefore to the state machine, all states look the same and are able to respond to the same set of messages. The state machine does not know or care which state is currently active. It only knows that the current state either implements or inherits all the methods that are the targets of messages being sent to it. The box on page 29 provides a brief review of objectoriented concepts and the HP IVI object-oriented environ ment.

/"to cause a transition to this */ / INT32 'group;

s

t

a

t

e

.

*

/ membership information. */

/ Data values assigned to the fields defined above jtate_rect = {

/ Initialization.

&_DzRect,

/ Pointer to dispatch tables.

objectname,

/ Pointer to name.

27,

/ State's id number.

FALSE,

/ State is NOT autoterminating.

_s_rect,

/ Message selector that causes / transition to this state.

groupmembership

Input Handling

/

/ Pointer to this state's group */

/ Pointer to group membership / information.

idState s_rect = (idState)&_state_rect; /'Apointertothisstate /"that is used by HP IVIBuild */ /* to access and manipulate */ / data In this structure. */

Inheritance. In HP IVIBuild, as in most object-oriented systems, state objects are arranged in a hierarchy. At the root of the hierarchy is a special state known as the root state (see Fig. 4). The root state in HP IVIBuild manages interstate transitions. Since the root state is at the top of the object hierarchy, it implements many more methods than the other states in HP IVIBuild. Using inheritance, the lower-level objects inherit all the methods from the root state. This inheritance mechanism is used to imple

Messages sent by the state machine to a particular state can result in either an interstate transition or an intrastate transition depending on the message that is sent. Interstate transitions are transitions among the various state objects of HP IVIBuild, and intrastate transitions are transitions within a particular state object. A new state becomes current by an interstate transition. Interstate transitions are handled by the state machine. All input in HP IVIBuild goes through the state machine. The state machine is an API callback function that is attached to all the components of HP IVIBuild's user interface and all of the workspace windows created by the user. The objects in the HP IVIBuild user interface are called userinterface objects, and the objects created by the user during an HP IVIBuild session are called user-workspace objects. Using this mechanism, HP IVIBuild is able to control the context of the user's input. This is an important require ment of any interactive design tool. The state machine performs the following functions: • It changes the active workspace windows when the user requests it. • It interprets the meanings (context) of the mouse buttons when they are pressed in the active workspace window according to a user-definable mouse button map. • It sends messages to the current state. • It manages the state stack. The state stack is an array of message selectors for the state objects. • It makes new states current and terminates others that have completed. The Current State

There is always a state that is active. This state is called

Root State

Fig. 4. A portion of the HP IVIBuild object hierarchy.

Fig. 5. The state stack.

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the current state. The current state is always the state to which the state machine sends any messages. It is up to the current state to provide a target method for any mes sages that the state machine may send it. The target method is located either by implementation or by inheritance. If no operation is in progress (i.e., only one state on the stack), the current state is the root state. If an operation is in progress, the current state is the state that implements that operation (e.g., creation of an object such as a polyline or widget). No state knows which state was current before it became current and no state knows which state will become current after it ceases being current. These rules were strictly en forced to ensure the black-box nature of each state's methods during design and testing. Once current, a state controls the context of the user's input according to a state transition mechanism of its own. These state transition mechanisms are called intrastate transitions and are controlled entirely by the state itself using a local variable called a subsidie. For example, mov ing forward or backward in a sequence of actions that are part of one particular operation, such as creating a polyline, is controlled entirely by the state itself. The substate mech anism is described later in this article. State Stack Management

During the execution of HP IVIBuild the states that are activated by the user are organized in a LIFO (last-in, firstout) stack (see Fig. 5). The state machine provides a mech anism to suspend operations in progress to do another op eration and then resume the suspended operation when the new operation finishes. The state at the top of the stack represents the current context of the user's input and is the current state. Only the current state can receive any messages. The maximum depth of the state stack is defined to be ten states. This is an adequate depth because there are other mechanisms in HP IVIBuild that prevent the state stack from growing to a depth of more than three or four states. The root state enters the state stack first and remains there during the entire execution of HP IVIBuild. Therefore, the root state is always in the stack regardless of the depth of the stack. At each interstate transition, the state machine checks the autotermination flags of each state in the state stack. If the autotermination flag is TRUE, that state is terminated immediately by the state machine and removed from the state stack. The state stack is then compacted and the state ending up at the top of the stack is started. If the autotermi nation flag is FALSE, only an action by the user can terminate the state.

ZtUSEFLDATA attribute of the object that received the event, which has a pointer to the message selector that, when sent to the a state, will cause an interstate transition to a new state. The state machine sends the message to the current state. This process works the same way for HP IVIBuild user-interface objects and user-workspace objects. except that user-workspace objects always send a hit mes sage to the current state. A window created by the user is the only user-workspace object that functions like a user-in terface object. A hit message results when a user presses a mouse button in a workspace window. If the current state can handle the message, the method that is called will either return a pointer to the current state or a NULL. This pointer is returned to the state machine as part of the normal message sending mechanism of the HP IVI object-oriented environment. States return pointers to themselves when they want to remain current. This will cause an intrastate transition. States return NULL when they receive an exit message and want to cease being the current state. This will cause an interstate transition. Fig. 6 shows a portion of the state transition process. Since the root state is the parent of all other states, the interstate transition process depends heavily on inheri tance. Each state inherits all the methods from the root state. When a state receives a message for which it does not have a method, the HP IVI object-oriented environment will search the current state's lineage (object hierarchy) until it finds the target method for the message. In the case of an interstate transition, the target method will always be found in the root state. The target method in the root state returns a pointer via the object-oriented environ ment's messaging system to the state object that is to be made the current state. This is the pointer that the state machine compares to the value of the pointer for the current state. When it sees that the two pointers are different, it

Button Release Event

DzState Machine (..., msg.selector)

1 Send Message to Current State

State Transition and Inheritance

As mentioned earlier, an interstate transition is the pro cess of making a new state (a state not currently on the state stack) the current state. The new state is placed at the top of the state stack and started by the state machine. The state transition process begins when an event occurs such as a button release over an object on the display. The first thing to happen is that the state machine function is called as part of the normal API callback processing (see page 23). The state machine function is passed a pointer to the

Send start Message to the Current State

Make New State Current

Continue Looking for Events

Fig. 6. The state transition process.

OCTOBER 1990 HEWLETT-PACKARD JOURNAL 35

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places the new pointer at the top of the state stack (making the state current) and sends a start message to the new state. Thus, by inheritance, every state object has the ability to activate any other state object. When an intrastate transition occurs, there is no change to the current state (i.e., the pointers are equal). The current state handles the incoming message itself. State Protocol

All states follow a specific protocol that is implemented in the state machine of HP IVIBuild. Fig. 7 illustrates this protocol. An interstate transition (Fig. 7a) occurs when the current state receives an exit message and it returns a NULL to the state machine indicating that it wants to cease being the current state. The state machine makes the new state the current state and sends a start message to the new state. The new state remains the current state as long as it con tinues to return a pointer to itself to the state machine (e.g., CurrenUState in Fig. 7b). Following this protocol allows a state to control the meaning of user input within its own context. Each state implements or inherits five standard methods that constitute its operational interface: start, hit, backup, undo, and exit. Start. As shown in Fig. 7, the start message is the first message a state receives before any other message is sent to the state (except exit). Hit. A state gets a hit message when the user presses a mouse button in the workspace window that is currently active. HP IVIBuild allows the user to construct and edit as many windows as desired but only one can be active at a time. To activate another window, the user only has to press a mouse button over the window that is to become active. Depending on their hit methods, states are classified as either multiaction or single-action states. A multiaction state requires the user to select multiple points in the active window to perform the operation im-

plemented by the state. An example of a multiaction state is one that allows the user to create polylines or splines. When the user presses a mouse button in the active window and a multiaction state is the current state, the action of the state is said to go forward. Fig. 8 shows the intrastate transition diagram for a multiaction state that translates objects. A single-action state does not require a hit in the active window to go forward. Single-action states can only do one thing. An example of this are selections (i.e., states that select certain kinds of objects for further operations). Once the class of objects that are to be selected is known, the objects are selected and no further input from the user is required. Any single-action state that receives a hit mes sage is terminated and removed from the state stack. The hit message is sent to the the new current state. Fig. 9 shows the intrastate transition diagram for all single-action states. Backup. All multiaction states implement backup. This is the reverse operation of a hit message because it allows the user to cause the action of the state to go backward over a previously sent hit. No single-action states implement back up. Undo. All states implement undo. Undo allows the user to back a state up to the point right after it received its first start. This has the effect of undoing any actions that had been performed by the state. Undo may also be sent im mediately after a previous undo to effect a redo operation. Exit. A state is sent an exit immediately before its removal from the state stack. This allows the state to reinitialize

Interstate Transition

return (Current_State)

Current State

Interstate Transition

backup return (NULL) start

return (Current_State)

(a) Intrastate Transition ( I n p u t User Workspace)

o v e r

b a c k u p

return (Current_State) start

backup

return (Current_State)

(b)

Fig. 7. HP IVIBuild state protocol, (a) An interstate transition, (b) Intrastate transition.

Fig. 8. Intrastate transition diagram for a multiaction state that cur objects. These states are substates of the cur rent state shown in Fig. 7b.

36 HEWLETT-PACKARD JOURNAL OCTOBER 1990

© Copr. 1949-1998 Hewlett-Packard Co.

itself for its next activation. The Substate

Once current, a state controls its own actions using a local variable called the substate. During a sequence of operations, the messages start, backup, hit, and undo may be sent repeatedly to the current state. These actions do not cause interstate transitions. Rather, they cause intrastate transitions. The current state does not change but the mean ing of the next input event may have to be interpreted differently depending on the sequence of messages the state has received since it was made current. The value of the substate is changed to reflect the context of the next hit, backup, or undo. Note that start is always sent after every action whether the action causes an intrastate or interstate transition. This is part of the protocol established for a state by the state machine. Uniformity

Great care was taken to ensure that the same actions have uniform behavior no matter which state is current. The HP IVIBuild team developed guidelines for developing states, and intrastate transition diagrams were developed before the development of a particular state so that the uniformity of actions could be assessed by the whole team. The result is a tool with very modular units of functionality that all behave in a consistent and intuitive manner.

The HP IVIBuild User Interface HP IVIBuild's user interface was designed as a collabora tive effort between the HP IVIBuild team members and the industrial design department at HP Software Engineering Systems Division (see the article on page 39). The objective of the collaboration was to design a user interface for HP

Interstate

return (Current_State)

Transition return (NULL)

IVIBuild that was both attractive and intuitive to the user. Besides the appearance. HP IVIBuild is structured to han dle native language support and user customization. One other interesting feature is that the HP IVIBuild user inter face presentation is not bound to the functionality until run time. Native Language Support and Customization

HP IVIBuild's user interface conforms to HP standards regarding support for native languages and cultures. All text that is presented to the user such as labels, prompts, and error messages is contained in message catalogs and is retrieved by HP IVIBuild at run time. To localize HP IVIBuild, the user only needs to change the contents of the catalogs. In general, these tasks are performed by HP per sonnel in the country whose native language is the target language. This way, text can be presented with as much context sensitivity as possible. Idiomatic nuances of text presentation are not lost (as they sometimes are with straight translations). Another feature of HP IVIBuild's user interface presenta tion is that colors, tiles, fonts, mouse button bindings and icons can be customized for individual users by modifying the X Window System configuration file .Xdefaults. This mechanism allows individual users to customize the pres entation of IVIBuild's user interface to suit their own needs (e.g., left-handedness, black-and-white display). Presentation and Functionality Binding

The presentation of the components that make up the user interface of HP IVIBuild (i.e., the buttons, menus, win dows, with and the functionality (the states) associated with these components are bound together at run time. The func tionality of HP IVIBuild, that is, the result of pressing a certain sequence of buttons, is not dependent on the user interface presentation. For example, in one user interface presentation, drawing a rectangle might be accomplished by selecting buttons labeled P1 and P2 for the lower-left and upper-right corners of a rectangle and typing the coor dinates into a pop-up dialog box. In another user interface,

Current State

Message Selector

Parameter

(ZtUSEH_DATA)

State Machine

Csllbsck Function

Fig. 9. Intrastate transition diagram for single-action states. These states are substates of the current state shown in Fig. 7b.

Ztlnput Calls...

Fig. 10. Binding HP IVIBuild user interface presentation to functionality at run time.

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drawing a rectangle might be a three-button sequence in which the user presses the Rectangle button and then clicks on the desired coordinates with the mouse. In either inter face, the state operations result in a rectangle. The binding of functionality to user interface presenta tion is done when HP IVIBuild starts up. At this time the objects (windows, menus, buttons, etc.) that make up the HP IVIBuild user interface are restored from a file. Pointers to objects (Ztlds) that activate states or send messages to the state machine are looked up using the name of the object that was assigned when the object was created with the API functions. This lookup is accomplished using an API function. When the Ztld for an object is returned, the mes sage selector for the state to be activated is retrieved. At this point a callback object (ZtCALLBACK_OBJ), which will call the state machine whenever an event occurs on the user interface object, is created for the user interface object. Also, the message selector from the state object is made an attribute (ZtUSEFLDATA) of the user interface object. Once the callback object is attached to the user interface object, the binding is complete (see Fig. 10). When a specified event occurs on a particular user interface object, the in terstate transitions described earlier occur. This scheme makes the state machine a callback for every IVIBuild user interface object and for every workspace window the user creates. Separating the user interface presentation from function ality means that the presentation can be developed inde pendent of functionality and the same functionality can be easily given a new presentation. New functionality can be added and tested in a straightforward way without worry ing about its presentation.

Acknowledgments

There were many challenges presented and many re wards gained in the development of HP IVIBuild. So many people added their inputs to HP IVIBuild that it is hard to mention them all. We would, however, like to thank Ron MacDonald (now at HP's Graphics Technology Division in Fort Collins, Colorado) who endured a year away from his home to work on HP IVIBuild. Every time a user draws a polyline or spline or makes a widget with HP IVIBuild, they will be using Ron's work. Thanks also go to Shiz Kobara of HP's Software Engineering Systems Division (SESD) who had the original idea that the user interface was a place where industrial designers could make a con tribution. Thanks to Steve Anderson and Jennifer Chaffee of SESD who followed through on Shiz's idea while Shiz was busy working on HP OSF/Motif. Our users will see their work every time HP IVIBuild displays its user inter face. Thanks to everyone who gave us their comments and encouragement.

Conclusion

HP IVIBuild was conceived with two objectives in mind: to be a powerful, easy-to-use tool to complement the HP IVI application program interface functions and to be the first API application and as such to provide feedback to the API development team. Both of these objectives have been accomplished. We believe that HP IVIBuild's func tionality and designed-in extensibility based on an objectoriented architecture are among the first for tools of this

type.

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Creating an Effective User Interface for HP IVIBuild The HP IVIBuild user interface was a collaborative effort between the software engineers developing the code for the product and a group of industrial designers who understand the requirements of an effective graphical user interface. by Steven R. Anderson and Jennifer Chaffee AMONG THE PRESENT and potential customers for HP's computer systems are companies that are in creasingly integrating computers into their manu facturing processes. However, the computer focus of these companies is more on solutions than on hardware and software development. To help provide these solutions on HP computer systems there are efforts within the company to encourage or enable independent software vendors (ISVs) to develop these software solutions. HP IVI from HP's Industrial Applications Center (IAC) is one such effort. Its purpose is to help ISVs build graphical user interfaces for their applications used in industrial applications. Why the need for a graphical user interface? Many of the operators and users of computer-based systems in an indus trial environment are not computer literate. They typically perform tasks like controlling an automated spray paint line, and the interfaces to the tools they use are typically knobs, dials, buttons and other physical and visual objects. A command line interface is a totally foreign approach for these people, and many of them refuse to deal with it. Whatever can be done to enable the interfaces to come closer to the users' current way of doing things is seen as having value. A graphical user interface is seen as having the greatest potential in making the interface familiar. Re cent developments in user interface technologies1 are very suitable for graphical user interfaces in industrial automa tion applications. Background

HP IVIBuild is a tool that enables users to develop graphi cal user interfaces interactively. Therefore, it seemed appropriate that it should have a graphical user interface. For this capability the HP IVIBuild developers decided to use the graphical user interface components that were under development at HP's Interface Technology Operation (ITO) in Corvallis, Oregon. These components are com monly called widgets.2 They include things like menus, scrollbars, pushbuttons, text-edit boxes, and radio buttons. They are the raw materials from which a graphical user interface is assembled. The HP IVIBuild team had no idea that using widgets would lead to collaborating with visual design professionals. Neither did we, the visual design professionals, know about the HP IVI team. We are the usability design and

engineering group of HP's Software Engineering Systems Division (SESD). We are former industrial designers who switched our design focus from designing hardware enclo sures to the area of user interfaces, plus one graphic design er. At the time our division was developing what would become the HP SoftBench environment,3 and we were also looking to ITO for the necessary widgets. Rather than pas sively waiting to see what they might provide, we were encouraged by our management to lend our professional expertise to the widget development, and ITO was openminded enough to listen to some of our ideas. We didn't begin with any proven graphic user interface expertise. We had done some design analyses of the leading graphical user interfaces. Also, coming from a background in which our experience and training forces us to process information visually gave us some ideas about how an ef fective graphical interface should look. And because our experience with software and computers was limited to being application users, we had some first-hand knowledge about the user interface requirements for users who are not software literate. Basic Principles

Three principles have established the foundation for graphical user interfaces in recent years, notably in officeoriented applications. The first principle is that it is easier for most people to have their alternatives presented to them in a manner that allows them to make choices rather than having to remember all of the alternatives. Choosing a com mand from a menu is often easier than remembering it. The second fundamental principle is that making these choices by some means of direct manipulation is often preferred over typing in text commands. Pushing a button or dragging a file icon into a folder icon or a trash can are two examples of direct manipulation. Finally, the third principle is to use metaphors from the real world. For exam ple, we know what to do with a pushbutton. In our analyses of the many graphical interfaces existing today, one of the impressions we formed was how confus ing they could be because of the flat and bland graphics. This is especially true in multiwindow environments in which there is a high degree of overlapping and the simi larity of the graphic images seems to blend all the images together into one confusing mass. We thought that creating

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greater visual distinctiveness between objects would signif icantly enhance a user's ability to keep things sorted out.

Scrollbars are hybrids, with a recessed groove containing raised controls. Menu bars look like large buttons with several labels on them. When the mouse drags over a menu item, it appears to raise, transforming itself into a button. When a menu item is selected by releasing the mouse but ton, the feedback mechanism is the same shadow reversal the pushbutton uses to appear recessed. Fig. 1 shows the transition from a total 2D appearance to a full 3D appear ance. Most people found this 3D appearance appealing. It be came a key factor in the subsequent adoption of the HP widgets by the Open Software Foundation (OSF) for their OSF/Motif standard user interface.4

3D Appearance of Widgets

Our first attempts to express widgets graphically were with the traditional black lines on a white background. To get away from the sameness mentioned above, some of the widgets were drawn to look three-dimensional and to look and act like pushbuttons. It soon became apparent that the displays of the future would not be constrained to simple black and white, and that larger areas of solid color could be used. This was a significant breakthrough. With the capability to use color, we added three colors to the black and white. By using light, middle, and dark versions of a color, we could make a button look very three-dimensional. This was achieved by making the top and left edges light, the flat surfaces the middle value, and the bottom and right edges dark. This technique makes it appear as though a light is shining on the button from the upper left. Another nice by-product of this technique is that by momentarily switching the light and dark colors when a button is selected, it actually appears to be pushed in. It was so effective that people got a little silly pushing buttons the first time they saw a working prototype. People intuitively grasp the notion that if something ap pears to protrude, it can be pushed or selected to generate some action. Widgets that accept or display inputs appear to be recessed. Noninteractive things like labels are flat.

A New Principle

The 3D appearance ends up creating a new fundamental graphical user interface principle: the visual separation and distinction of what we call user space and interface space. User space is where the user's inputs go, or where the user performs work. Examples are the space provided in a word processor for entering text, or the space provided in a paint program for creating images. It also includes those areas where the user is asked to input data like the name of a file. The rest of the screen is the interface space, or the visual manifestations of the applications and/or the operating sys tem. Included in this category are items like window frames, dialog boxes, tool panels, menus, and the metaphor-

Conuert Conuerted DOS file will be displayed in R1...JIO. Conuert From DOS File To DOS File

File Name: enter text here Conuert Conuerted DOS File will be displayed in HI. ..,11 II.

Type of Conuersion

Conuert . From DOS File

File Name: enter text here

1 To DOS File Type of Conuersion

Conuerted DOS file will be displayed in R1...J10.

Total 2D

Displayed Directory:

Type of Convei"

J

Partial 3D

Full 3D

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Fig. 1 . Transition from total 2D ap pearance to a full 3D appearance.

ical desktop. The interface space, whether controlled by the application or the operating system, is where all of the 3D effect is found. In office-oriented applications, which have been driving the graphical user interface movement to date, the 2D user space is usually dominant in terms of screen area. The main focus of these applications is generally to provide a tool that allows the user to create different forms of docu ments such as mail messages, memos, charts, spreadsheets, overhead slides, and newsletters. Based on these applica tions, the user space is perceived to be the WYSIWYG equivalent of some sort of paper document, whether a small notepad or a large drawing. It is predominantly two-dimen sional, which is appropriate because the resulting docu ments are also two-dimensional. There is an emergence of graphical user interfaces in which the interface space dominates because the main function of the applications is not document creation but some form of process setup and control. Examples include things like configuring and running a set of test instru ments, or monitoring and controlling a complex tempera ture control system or an assembly line. HP IVIBuild is geared to create interfaces of this latter type. The 3D widgets (or OSF/Motif widgets) are particularly well-suited to this type of interface because the physical reality they convey is much closer to the mental model most people have of activities that are control-panel oriented. Fig. 2 shows one window for an office-oriented application and another for an instrument control panel.

control-panel-like layouts with animated graphics and numerous controls. These capabilities were not obvious in the original interface shown in Fig. 3.

HP IVIBuild before Redesign

Collaboration

In the early stages of development, the HP IVI team used the initial version of the widget code from HP's Information Technology Operation. The early results of their using this code produced the 3D appearance shown in Fig 3. Unfor tunately the 3D effect was largely lost and the user interface was hard to understand. This early result was not a surprise because the HP IVIBuild team had not yet had enough experience with widgets and consequently had little notion of how to achieve and use the 3D effect. They were also unfamiliar with many of the standard techniques and prac tices for creating graphical user interfaces. Our group had concurrently been using the 3D widgets with our own HP SoftBench tools. That successful experi ence plus the acceptance of HP widgets for OSF/Motif gave us a certain amount of credibility. As a result we soon found ourselves in contact with the HP IVIBuild team. Like our experiences with the ITO team in the development of widgets, the HP IVIBuild people were very open-minded in letting us get involved with their product. HP IVIBuild was different for us in that it not only uses conventional widgets to create a graphical user interface, but it can also create graphic objects that behave like widgets. What this means is that buttons and scrollbars can be supplemented with graphic representations of ob jects that can change to reflect current status. For example, a graphic image of a storage tank can change to show the current level of the liquid it contains, or an assembly line schematic can be changed to reflect the status of each work cell. The output of HP IVIBuild can range from simple windows with menu bars and dialog boxes to very complex

The Structure of HP IVIBuild

The HP IVIBuild user interface is divided into three parts: a utility box, a tool box, and a workspace. The Utility Box. This area holds the menu bar, a prompt window, several status indicators, and some commonly used commands in the form of pushbuttons. The Tool Box. This area is like a palette of various graphic or widget creation tools. It has three modes: graphics, widgets, and models. The graphics mode functions like a typical paint program, displaying numerous drawing tool buttons as well as mechanisms for displaying and selecting items such as colors, patterns, and line weights. The widget mode is used for creating and specifying the widgets. The models mode is used to get access to models, which are templates or libraries of previously created work. Fig. 4 shows the utility box and tool boxes at an early point in the design stage of HP IVIBuild. The Workspace. This is the area in which the user does the work of building a user interface. In this area graphic or widget objects are put together on a kind of three-dimen sional sheet of paper. After assembly, they are stored away for use as finished products or as models for reuse or mod ification. For example, a simple dialog box might be used as a template for other dialog boxes, eliminating the need to start each one from scratch. The early efforts by the industrial designers focused on sorting out the functionality found in each of the HP IVIBuild areas and then finding reasonable ways of present ing each area. The utility box and the tool box visual layouts received the most attention. One of the first steps was de termining the menu structure in the utility box. Certain conventions and many examples exist in industry showing how applications organize and perform activities like edit ing and filing — for example, the locations of commands like cut, copy, paste, and quit in a word-processing package. And certain conventions exist in terms of dialog box layout, like where the OK, cancel, and help buttons should go. We followed accepted general practices wherever possible, and tried to develop acceptable solutions where no previous models existed. The tool box with its various modes was probably the most complex job. The final layout chosen for the tool box owes many of its approaches to showing status and offering choices or functions to existing de facto standards for paint programs. There were instances where we were forced by technical limitations to deviate from these standards. For example, a simple draw tool like the one used to draw a rectangle typically requires a decision about whether the rectangle is to be filled in or left as an outline. A typical solution is to have one button with a rectangle on it, with the left half hollow and the right half filled (what looks like one button is in fact two buttons). In our case the widgets wouldn't allow that approach, so we ended up with a separate button to turn the fill function on or off. Fig. 5 shows the design recommendation for the utility and

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This case simple typical Office-oriented application window, in this case a simple woid planning document. Olher types of applications which would be similar to this are spreadsheets, chartingand graphing programs, various drawing and paint programs, desktop publishing applications, as well as CAD programs. All of these share certain characteristics: they want to be of most WYSYWYG character, and the final product of using them is most often a two dimensional piece of paper, It is the entirely appropriate that the User Space in which the user does the document creation resembles the final product—a sheet of paper. It is large, white, fiat, uses black "ink," etc. Unless of course, it is an application that creates colored documents, The main point is that two dimensional User Space tends to dominate the user interface. The other window shows a different sort of application. Here the focus is on doing tasks like is up and running tests or making measurements, It is applications like this that IVlBuild is designed to create. Because the User Space is so limited, the three dimensional Interface Space dominates, This ends up being a good feature, as the applications can end up looking very much like the older hardware products their users are familiar with.

Fig. 2. One window with a typical 2D office-oriented application and the other window showing a 3D instrument control panel.

tool boxes at a later stage in the development. Colors were another area where the designers had some thing to contribute. We had some color schemes in hand from our earlier work on widgets as well as from our work with HP's SoftBench product. This greatly simplified the tricky decisions required to convey the 3D quality of widgets. We provided the color names and RGB values that had to be assigned to each widget component to make the 3D effect work and provide a pleasant overall interface.

Fonts were also important. Graphical user interfaces in general, and the 3D widgets in particular, are very much dependent on good fonts to be successful. While the popu lar notion of a graphical interface centers on icons, most of the work is still done with words, and good pro portionally spaced fonts make words work better. The HP IVlBuild team decided to use some display fonts that had been created by HP expressly for 3D widgets. These fonts provided both behavioral benefits (text properly centered

Fig. 3. A very early version of HP IVlBuild when the design team first began to use widgets.

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Fig. 4. The visual designers' first proposal for the HP IVIBuild user interface.

in widgets, text baselines lined up, etc.) and a consistent, high-quality look. The designers also created all of the bit maps and icons associated with the tool boxes and other aspects of the product. One challenge with many of the tool box buttons, especially for those in the widgets mode, was to express the 3D nature on a small scale and with only two colors. The illusion of using three colors was achieved by using a light and a dark color and then introducing a dithered pattern that the eye blends together to form a third color (see Fig. 6). The final area of collaboration was to do something visual and graphical to help explain and sell HP IVIBuild. Some sample screens were created that express how HP IVIBuild can actually be used. With just a little prompting on how

to use the 3D effect, a designer used HP IVIBuild to create two sample screens for each of seven potential application areas. These compelling images, achieved through the use of the actual tool, have done more to explain HP IVIBuild and its capabilities than a volume of marketing brochures. One of these sample screens is shown in Fig. 2 on page 8. Conclusion

We learned a few things as a result of this collaborative exercise. One is that experts often have problems com municating their concepts and ideas to nonexperts. In this case we had two groups of experts. We found that it was important to have a main conduit or interpreter between the user interface designer and the rest of the software team. Without someone to answer all of the questions the

Fig. 5. A later version of the user interlace after incorporating some of the implementation limitations.

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Fig. 6. Achieving the 3D effect with only two colors.

user interface designer asks, and interpret the various dialogs with the team members, the communication pro cess really breaks down. One designer interfacing with a half-dozen individual team members means a half-dozen different interfacing styles. Another lesson we learned is how important it can be to have an early vision of what you are trying to do. Tools exist that enable designers to create this vision and user scenarios quite quickly. The power and usefulness of these visuals should not be underestimated. They are powerful catalysts for people's thinking and communication. Once these are analyzed, discussed, and modified, the product is better understood by all concerned. Only at this point should the interface coding begin. The mistake should not be made of bringing the visual design help in at the very end to fix up the icons. Chances are the flaws go far beyond cosmetic graphics, and at this point the investment has been so great that significant changes are nearly impossible. Acknowledgments

Acknowledgments are due some of the key people who are responsible for this successful collaboration. First, to Steve Joseph and Chuck House of SESD, for letting us work

outside of our own division. Both of them have been amaz ingly farsighted in encouraging us to work wherever we can use our expertise to help HP product development. At HP's Industrial Applications Center (IAC) where HP IVI was developed, thanks go to section manager Chuck Robin son, project manager Vicki Mosely, and team members Steve Witten, Pam Munsch, Scott Anderson, and Ron Macdonald for their patience and openess. And within IAC mrketing, special thanks to Dushyant Sukhija and Andy Lerner for their enthusiastic adoption of visual selling tech niques. Finally, a special acknowledgment to the other members of the industrial design team, Barry Mathis and Shiz Kobara. References 1. A.O. Deininger and C.V. Fernandez, "Making Computer Be havior Consistent: The HP OSF/Motif Graphical User Interface," Hewlett-Packard Journal, Vol. 41, no. 3, June 1990, pp. 6-12. 2. D.L. McMinds and BJ. Ellsworth, "Programming with HP OSF/ Motif Widgets," Ibid, pp. 26-35. 3. M.R. Cagan, "The HP Softbench Environment: An Architecture for a New Generation of Software Tools." Ibid, pp. 36-47. 4. "OSF/Motif," Ibid, p. 8.

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Authors

General Motors Corp., and the HP Graphics Inter face System. Roger earned a BA degree in micro biology in 1 976, an MS degree in microbiology in 1978, and an MS degree in computer science in 1981, all at the University of Hawaii. Born in Honolulu, he lives in San Jose, California, where he enjoys volleyball and ballroom dancing.

October 1990

sistant at Lawrence Berkeley Laboratories. A member of the ACM, her professional interests in clude computer graphics, parallel processing, and networking. She received her BS degree in physics in 1975 from the University of San Francisco and her MS degree in computer science from San Fran cisco State University in 1 989. Born in Saigon, Viet nam, she is married, has a son and a daughter, and lives in San Francisco.

Mark E. Thompson ! Software engineer Mark Thompson- joined HP's Data Systems Division in 1 980, where he worked on disk diagnostics and util ities, I/O drivers for HP 1000 computers, and a t; |Wr ^ quality decision manage ment program. For the HP IVI project, he was respon sible for graphic objects, the error handler, and the quality function deployment analysis. His profes sional interests center around 2D and 3D graphics. Mark received his BS degree in computer en gineering from Boston University in 1980. Born in San Francisco, California, he lives in Berkeley. His interests include automobile restoration, beer mak ing, photography, bicycling, gardening, hiking, camping, and audio electronics.

1 = HP IVI Toolkit :

David G. Wat hen I User interface design, 'graphics, and artificial ¡nl telligence are the profes sional interests of David Wathen, a software en' gineer who developed eni hancements for the HP IVI Droject. He joined HP's In dustrial Applications Center in 1989, shortly after he received a BS degree in computer science and applied mathematics from the University of Colo rado at Boulder. Before joining HP, he was a soft ware designer for the National Center for Atmos pheric Research (NCAR), where he built an X1 1 window interface to NCAR graphics. David was also an advanced interface intern at US West, where he worked on future telephone projects. Born in Littleton, Colorado, he resides in Sunnyvale, California, where he enjoys Tae Kwon Do, skiing, 4-wheel driving, backpacking, and traveling.

6 ~ HP IVI !

I Roger Lau, a technical mar keting engineer at HP's InI dustrial Applications I Center, provided technical 1 support for HP IVI. Roger 1 joined HP's Data Systems Division in 1981. He has | worked as a development engineer and a technical "W lead in the development of the HP Advanced Graphics Package, the HP Device Independent Graphics Library, the HP Manufacturing Automation Protocol pilot for

Mydung Thi Iran BB| Software engineer Mydung Iran was responsible for widget development, test ing, and native language support for the HP IVI proj ect. She joined HP's Indus trial Applications Center in 1988. Mydung has au thored or coauthored five technical articles on distrib uted processing, particle dosimetry, space radia tion, and nuclear track detectors. Before joining HP, she was a research physicist at the University of California at San Francisco, and a graduate as-

21 =1 HP IVI API Design Pamela W. Munsch Pam Munsch, a software development engineer on the HP IVI project at HP's Industrial Applications Center, worked as a de velopment engineer on an 1C testing project shortly after she joined HP's Santa Clara Division in 1 983. She is now an R&D project man-

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ager working on HP IVI . Pam received her BS de gree in computer science in 1 983 from the Univer sity of California at Santa Barbara. She is married, lives in the city of her birth, San Jose, California, and enjoys playing volleyball.

Warren I. Otsuka ^•CL^^B As an R&D software en•^^ "**-^ gineer at HP's Industrial Applications Center, Warren Otsuka was responsible for input handling and widget ob jects for the HP I VI project. % I After joining HP's Data Sysj+^jf^ *. terns Division in 1978, he worked on support for the HP F/1000 forms management tool and HP F/1000/HP-UX products. Before joining HP, Warren was a project lead for user interface development and an engineer on a document project for Docugraphix, Inc., and he provided system support for the STAR-100 operating system at Control Data Corporation. He earned a BS degree in computer science from the California State University at Chico in 1972. Born in Kona, Hawaii, Warren is mar ried, has a daughter, and lives in Campbell, Califor nia. He enjoys family activities, reading mysteries, and photography.

Gary D. Thomson ¡Software development en gineer Gary Thomsen, who joined HP's Data Systems Division in 1979, helped design widget classes for the HP IVI project. Before that, as an R&D software engineer, he provided supP°rt f°r the HP 1 000 Series i I ii·IP f Forms/1000 product, and as an R&D product design engineer, he designed the HP 1000 Series A hardware packaging. Gary earned his BA degree in mathematics from San Jose State University in 1 977. He is married, lives in San Jose, California, and enjoys Softball, biking, and woodworking.

32 ~HP IVIBuild

Data Systems Division in 1 978. Initially, he worked on Datacap/1000 and supported HP 307x termi nals, and then developed an energy management system for HP using the PMC/1 000 system. Before joining HP, he worked for Environmental Research and Technology, Inc., where he compiled a data base of airborne sulfate/particulate measurements for the Electrical Power Research Institute's study of acid rain. Steve is a frequent contributor to INTEREX, the HP users group, writing technical ar ticles on object-oriented programming. A member of the Institute of Industrial Engineers, his profes sional specialty centers around object-oriented technology. He received a BS degree in computer science in 1 974 and an ME degree in industrial en gineering in 1976 from the California Polytechnic State University in San Luis Obispo. Born in Bakersfield, California, Steve is married, has two daughters, and lives in San Jose. His hobbies include computers and reading detective novels.

Jennifer Chaffee

Hai-Wen L. Bienz Hai-Wen Bienz was re sponsible for the develop ment of the graphic objects and dynamics in the HP IVI application program inter face. She joined HP in 1 985 and served as a publica tions engineer at HP's Santa Clara Division, and \^K^H later as a marketing en gineer for the Strategic Grants program at HP Laboratories. Hai-Wen's professional interests in clude designing user interfaces and software tools to enhance productivity. Before joining HP, she was a coop student and engineer at General Motors Corp. , where she developed real-time digital con trol systems. Hai-Wen earned a Bachelor's degree in electrical engineering from the General Motors Institute in 1 983 and an MS degree in electrical en gineering from the University of Illinois at UrbanaChampaign in 1984. She is married and lives in Naperville, Illinois. Her interests include moun taineering, skiing, photography, cooking, and hiking.

39 1= HP IVIBuild User Interface :

Steven P. Witten

Steven R. Anderson The principal architect of the HP IVIBuild portion of the HP interactive Visual In terface, Steve Witten im plemented the state ma chine and window and model handling for the proj ect. Now an R&D engineer at HP's Industrial Applica tions Center, he joined HP's

system furniture products, including the HP 9221 4 CAD worktable. Now a lead designer on the HP VUE graphical environment for HP-UX worksta tions, Steve's professional interests include making computers visually appealing and fun to use. He is named as an inventor on an industrial design patent for a Xerox copier, coinventor of a product design layout patent on a color printer concept from HP Laboratories, and coinventor on a patent application for HP 3D widgets and extensions. Steve received a BS degree in industrial design from the University of Bridgeport in 1966. Born in Hibbing, Minnesota, he is married, has two chil dren, and lives in Mountain View, California. He en joys playing golf at dawn on Sundays, bicycling to work, and activities with his children.

Visual interface designer Steve Anderson helped des'9n the user interface for the HP IVIBuild product. He joined HP's Calculator Products Division in 1976 and was responsible forthe industrial design package for the HP 9845 computer/ controller and computer

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Jennifer Chaffee worked on the user interface for the HP IVIBuild product at HP's Industrial Applications Center. She joined HP in 1988 and worked on HP OSF/Motif and the HP New Wave Office. Before com ing to HP, she worked in the industrial design and user interface department of the Xerox Corporation copier division. A 1 985 graduate of the Rochester Institute of Technology with a BFA degree in graphic design and art history, Jennifer's profes sional interests include the visual design of com puter user interfaces. Born in Fort Worth, Texas, she lives in Sunnyvale, California. She enjoys paint ing, pastels, pottery making, backpacking, travel ing, and photography.

49 = BaFe Preselected Mixers Michael J. Levernier ^^f^^ Development engineer ^BH|& Mike Levernier was responf sible for the design of the W — - I HP 1 1974 filter drive cir cuitry and for HP 1 1 974 test development. He joined HP's Signal Analysis DiviI sion in 1984 as a manufac turing engineer respon sible for the HP 8557A and HP 8559A spectrum analyzers. Following that, he worked on the microwave and RF front-end mod ules of the HP 70000 modular spectrum analyzer family. He also served as an HP regional sales de velopment engineer. Mike received his BS degree in 1983 in electronic engineering from California Polytechnic State University, San Luis Obispo, and his MS degree in 1986 in electrical engineering from Stanford University. Born in Sacramento, California, he lives in Windsor, California. His hob bies include windsurfing, skiing, and racquetball.

Robert J. Matreci Bob Matreci served as R&D project manager during de velopment of the HP 1 1 974 ected spectrum analyzer RF sections. He joined HP s Signal Analysis Division in 1978 as a pro duction engineer in micro wave microelectronics. After transferring to the R&D lab. he developed millimeter-wave acces sories for spectrum analyzers, including the HP 1 1 970 Series waveguide harmonic mixers. Before joining HP, he developed avionics test equipment for weather radar. Bob has authored two technical papers and is named an inventor on a patent re lated to the preselected RF sections product He is a member of the IEEE and is the program chair man of the local subsection. Born in Chicago, Il linois, Bob is married and resides on Riebli Moun tain near Santa Rosa, California. His interests in clude sailing on San Francisco Bay and near the Northern California coast, and volunteer testing of emergency beacons for NASA's Search and Rescue Satellite (SARSAT).

59 — Hexagonal Ferrites ; Dean B. Nicholson 1 For the past eight years, | Dean Nicholson has grown barium ferrite single crys tals, processed them into spheres, and designed fil ters using the spheres. ' Since he joined HP's Micro wave Technology Division | ¡n 1980, he has also been responsible for charac. and sapphire substrates. He re ceived his BS degree in 1980 with dual majors in electrical engineering and materials science en gineering from the University of California at Berke ley. Dean is an author or coauthor of four technical papers on barium ferrite-tuned filters and oscil lators. He is named an inventor on a patent on the four-sphere filter configuration that is part of the HP 11974 spectrum analyzer RF sections product. Born in Orange, California, Dean is married, has three daughters, and lives in Windsor, California. He enjoys diving, hiking, and camping.

62— HP DIS: Kent L. Garliepp Specializing ¡n computeraided manufacturing, Kent Garliepp worked on de_ sign, development, and !jlà testing of HP DIS software • for HP 9000 computers as I a member of HP's Industrial | Applications Center in Sun lit nyvale, California. After joining HP ¡n 1959, he pro

vided computer support for the solid-state labora tory of HP Laboratories, and 1C manufacturing soft ware support at HP's Cupertino Integrated Circuits Operation. More recently, he helped design soft ware for truck manufacturing at HP's Advanced Manufacturing Systems Operation. Born in Palo Alto, California Kent is married, has four children, and lives in Capitola. California His interests in clude bicycling, radio-controlled models, and water-color painting.

Kathleen A. Fulton , After joining HP's Engineer ing Productivity Division ¡n • 1984. software engineer I Kathy Fulton helped dei| velop the equipment con• trol portion of HP's Semiconductor Productiv ity Network. She also de| signed and coded the conIH^^BH figuration, initialization, and run-time portions of the HP DIS product, and is now testing and maintaining HP Sockets software at HP's Industrial Applications Center. Before joining HP, Kathy was a semiconductor fabrication en gineer at Burroughs Corp. and a software develop ment engineer at Trilogy Corp. and Amdahl Corp. A member of the IEEE, she received her BA degree in 1 975 ¡n applied physics and information science with a specialization in computer science from the University of California at San Diego. Born in Reno, Nevada, Kathy is married and lives in Cupertino, California. Her interests include traveling to unusual locations, reading science fiction, and quilting.

John U. Frohlich As a member of the software development team at HP s Industrial Applica tions Center. John Frohlich helped develop the HP DIS product. He joined HP in [ 1976 at the company s Op toelectronics Division, and helped develop machine language programs for cal culator-based systems to test LED display devices He also has worked on several versions of the RTE operating system for HP 1000 computers and on ATS/1000 software John received his BSEE de gree in 1 963 at the Lucerne State College of Tech nology in Switzerland He is a member of the IEEE Born in Switzerland, he lives ¡n Cupertino, Califor nia, and enjoys mountain hiking, biking, and listen ing to old jazz recordings

73

R, L, C Measurements

Asad Aziz ^^^^^ Now a marketing account J^H ^^^ manager for HP's Circuit ^ 1 T e c h n o l o g y G r o u p , A s a d Aziz was previously in R&D, ^•nflMl where he worked on the de sign, layout, modeling, and Vy electrical model verification of the PCX CPU package ^^^^^^^^ Before that, he worked on .^•IHIHHBkk packaging R&D for HP PARISC computers, and on TAB design and electrical modeling. Asad joined HP's Colorado Integrated Circuits Division in 1 985, shortly after he graduated from Brigham Young University with a BSEE degree in 1 984. He received an MBA degree ¡n 1 990 from the University of Denver. A member of the IEEF. he has coauthored two technical papers on packag ing. Born in Lahore, Pakistan, Asad is married and lives ¡n Fort Collins, Colorado. He enjoys squash, bicycling, and windsurfing

Irene Skupniewicz For the past four years at HP, Irene Skupniewicz has worked as an R&D software . • « ~ engineer in the develop ment of manufacturing ap plications Currently, she is in the Manufacturing Appli cations Group working on the Device Interface Sys tem and Software Integra tion Sockets, two products that are part of HP's in dustrial precision tools for HP 9000 computers. Irene earned a BS degree (1981 ) in industrial en gineering from the University of Wisconsin, and an MS degree (1987) in electrical engineering from Carnegie-Mellon University ¡n Pittsburgh. Before joining HP, she worked with Unimation/Westinghouse ¡n Pittsburgh to develop robotic systems. Born in Racine, Wisconsin, Irene lives in Cupertino, California. For many years, she has been a "die hard" runner and enjoys meeting other HP people through her membership in the HP Running Club.

Ravi Kaw I Ravi Kaw developed a methodology to measure R, L, and C parameters in VLSI packages using coax ial probes rather than cusI torn-designed boards. | Since joining HPin 1982, he I has served as a product engineer for DRAM and math chips and as a semiconductor process engineer, and has worked on package measurements and modeling re search. Before joining HP, Ravi was a lecturer at Kashmir University and an engineer at the Jet Pro pulsion Laboratories and Fairchild Semiconductor Corp. He is the author of 14 technical articles on device physics, device modeling, packages and

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systems, and measurement methods. His work has resulted in two pending patents on packaging structures and systems and measurement methods. Ravi is a member of the IEEE and the International Packaging Society. He received his BE degree in 1966 in electronics and telecommunications from Jabalpur University, his MSEE degree in 1972 in microwave solid-state devices from Marquette Uni versity, and his PhD degree in 1 978 in solid-state electronics, quantum electronics, and microwaves from the University of California at Los Angeles. Ravi is a member of the board of directors of a local Hindu community and cultural center, and a Sun day school teacher. Born in Srinagar, Kashmir, India, he is married, has two children, and resides ¡n San Jose, California. He enjoys jogging, garden ing, hiking, and reading.

David W. Quint Before Dave Quint joined HP's Desktop Computer Di vision in 1979, he helped design nuclear reactor control systems for Westinghouse-Bettis Atomic Power Laboratories. As an HP R&D design engineer, he developed tape automated .' bonding (TAB) and pin-grid array (PGA) packaging for VLSI circuits. He is now an R&D engineer working on integrated circuit packaging at HP's Colorado Integrated Circuits Di vision. Dave's work has resulted in two patents, one describing a method of sampling a 1 00-GHz opti cal pulse stream, and another for a method of de positing tungsten for integrated circuit intercon nects. His professional interests include integrated circuit process engineering, electromagnetic fields, circuit analysis, and optical electronics. He published a paper in the Journal of Applied Physics while at MIT, and has coauthored three conference papers on electronic packaging. He received his BSEE degree in 1972 and MSEE degree ¡n 1976 from the University of Wisconsin at Madison, and earned a PhD degree ¡n 1979 from the Massa chusetts Institute of Technology. Dave served as a weather observer ¡n the U.S. Air Force from 1 963 to 1 967, attaining the rank of sergeant. Born in Barran, Wisconsin, he is married, has two boys and a girl, and resides ¡n Fort Collins, Colorado. His hob bies include weight lifting and taking karate lessons with his children. Dave says they hold advanced belts ¡n the martial arts, but he's still working on the basics.

Frank J. Perezalonso Frank Perezalonso specializes in hardware design engineering and analog circuit design and measurements. He joined HP Laboratories in 1 984 as a semiconductor process technician, and is now a member of the technical staff of HP's Circuit Tech nology Group. He worked on the electrical charac terization of the high-performance HP 408C PGA integrated circuit package. In the past, Frank was involved in E-beam lithography process develop ment, evaluation and test of HP's membrane probe card, and test methods for the electrical characteri zation of 1C packages. Before he joined HP, he worked on semiconductor processing for Fairchild Semiconductor Corp. and as an instructor ¡n math, physics, and semiconductor processing at Foothill College in Los Altos, California. He studied semiconductor processing at Foothill College, re ceived a BSEE degree in 1 985 from the University of Santa Clara, and expects to receive his MSEE degree in December. Born in Managua, Nicaragua, Frank is married, has a daughter, and lives in San Jose, California. He enjoys sports and teaching.

78 — Statistical Simulation Chee K. Chow Manufacturing develop ment engineer Chee Chow specializes ¡n computerintegrated manufacturing, manufacturing data bases, and analog and microwave circuits. He joined HP's Santa Clara Technology I Center ¡n 1984 and has n done research in statistical circuit simulations for circuit designs. He recently transferred to HP's Microwave Semiconductor Division. In the past, Chee worked on bipolar high speed circuits at HP, and researched coal conver sions and materials at Washington State University, where he received his PhD degree in 1 974 ¡n phys ical chemistry. He also earned an MS degree ¡n 1984 ¡n electrical engineering from Oregon State University. Chee is the author of 1 5 technical arti cles on fuel processing, physical chemistry, and electronics.

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82 _ Air Flow Analysis :

As manager of computer fluid dynamics applications at Cray Research, Inc., Kent Misegades collabo rated with HP on airflow simulation in the HP 9000 Model 850 computer. At Cray Research, he is re sponsible for all fluid I dynamics-related applica tions in the aerospace, automotive, metals, elec tronics, and chemical industries. His experience also includes work as an aerodynamicist for Dornier GmbH ¡n West Germany from 1980 to 1984. A member of the AIAA, Kent's professional in terests include aircraft design and fluid mechanics. He is a graduate of Auburn University with a BSc degree (1 979) in mechanical engineering, and has an ME degree (1 980) in fluid dynamics from the von Karman Institute ¡n West Germany. Born ¡n Los Angeles, California, Kent is married, has three chil dren, and resides ¡n Eagan, Minnesota. His hob bies include aircraft design and radio-controlled sailplanes.

Vivek Mansingh ¡Since joining HP's Systems Technology Division in 1987, Vivek Mansingh has performed research and I development in thermal i management of electronic I equipment in the comI pany's mainline systems ^^^ j lab. Using finite-element modeling, he analyzed three-dimensional air flow in the HP 9000 Model 850 computer. Before joining HP, Vivek taught at Lehigh University from 1 986 to 1 987. A member of the ASME, the IEPS, and the CHMT, he has au thored or coauthored 1 2 technical publications on thermal fluids, and is named an inventor on a pend ing patent. He earned his MS and PhD degrees in 1 986 from Queen's University in Canada, studying mechanical engineering and specializing ¡n ther mal fluids. Born in Fatehpur, India, Vivek is married, has two children, and lives in Santa Clara, Califor nia. He enjoys traveling with his family and singing Indian music with a professional group. His hobbies include jogging, tennis, and badminton.

26.5-to-75-GHz Preselected Mixers Based on Magnetically Tunable Barium Ferrite Filters A new resonator material — barium ferrite — and a new foursphere design are featured in a series of magnetically tunable preselection filters for the millimeter-wave frequency range. by Dean B. Nicholson, Robert J. Matreci, and Michael J. Levernier THE NEED FOR HIGHER PERFORMANCE has driven the frequency ranges of systems and components from the microwave range (under 30 GHz] into the millimeter wavelengths (30 to 100 GHz). Moving to higher frequencies makes it possible, for example, to increase the antenna gain of small reflectors and to improve the spatial resolution of imagers. The benefits of the move to milli meter-wave bands are being felt in many fields, especially communications, remote sensing, and defense.1 The spectrum analyzer, a calibrated receiver with vari able resolution, is an important basic tool for testing and troubleshooting such systems. Microwave spectrum analyzers use advanced technology to provide accurate, unambiguous frequency-domain measurements. HewlettPackard has extended these measurements into the mil limeter-wave bands. A new series of preselected spectrum analyzer RF sec tions, the HP11974 Series preselected mixers, makes milli meter-wave spectrum analyzer measurements faster and easier by removing image and multiple responses from the spectrum analyzer display, thereby eliminating the need for complicated signal identification routines. Each RF sec tion consists of a mixer to down-convert millimeter-wave signals into the intermediate frequency range of HP micro wave spectrum analyzers, and a magnetically tuned pre selection filter to remove unwanted signals. The preselec tion filter uses barium ferrite resonator material, doped so that it starts resonating at the beginning of the waveguide band (see article, page 59). Table I lists the four preselected RF sections and their frequency ranges. Each RF section covers a full waveguide band (±20% bandwidth), one of the four standard bands from 26.5 to 75 GHz. The HP 11974 Series preselected mixers are compatible with the HP 8566B spectrum analyzer, the HP8563A port able spectrum analyzer, the HP 70000 modular measure ment system with the HP 70907B external mixer interface module, and other HP microwave spectrum analyzers. They provide a displayed average noise level at 10-Hz bandwidth that is lower than -106 dBm in the A, Q, and U bands and lower than -95 dBm in the V band. Image rejection is better than 55 dB in all four bands.

Table I HP Millimeter-Wave Preselected Spectrum Analyzer RF Sections (HP 11974 Series Preselected Mixers)

Methods of Extending the Frequency Range

There are three principal ways to extend the frequency range of a microwave spectrum analyzer. The first method, shown in Fig. la, uses a classic superheterodyne receiver front end. A tracking preselector and a local oscillator (LO) both sweep the same frequency span, separated by the in termediate frequency (IF). The preselector prevents spuri ous responses, such as images or intermodulation products, from being displayed. The LO must be phase-locked and have reasonably low phase noise. To use this method, highQ resonators and active devices maintaining negative resis tance across the full waveguide bands would have had to be developed. The design would have been intricate and expensive. These technological difficulties eliminated this method from consideration for the HP 11974 Series. Fig. 2 shows where this type of millimeter-wave extender would interface with the mainframe microwave spectrum analyzer. A block down-converter, shown in Fig. Ib, eases the local-oscillator problem by using one fixed oscillator per band instead of the swept LO of the superheterodyne re ceiver. With this down-converter, input RF frequencies are converted to an identical but lower frequency span (swept IF). The swept IF can be arranged to be within the range of the microwave spectrum analyzer. Even though the res onator and the active devices are operated at a single fre quency, designing for performance and cost still poses a formidable problem. Also, this method lacks a tracking preselector, so the first mixer is subject to distortion caused

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Tracking Preselector

Fundamental Mixer

RF In 50 to 75 GHz

®— (S

Swept LO 50.32 to 75.32 GHz Sweep

Tune Ramp In (a)

(Swept) D) IF Out 1 to 26 GHz

RF In 50 to 75 GHz Phase Detector

Wideband Preamplifier

Ref

Block Diagram

(b) Harmonic Mixer n=14

RFIn 50 to 75 GHz

LO In 3.54 to 5.33 GHz Tune Ramp

(c)

by multiple signals and even single input signals. The wide span of the IF can cause another problem. It requires a very wide-bandwidth IF amplifier to improve the sensitivity of the microwave analyzer, which is used as a variable IF strip. The preselected harmonic mixer version of the super heterodyne front end, shown in Fig. Ic, provides a reason able compromise. The preselector protects the mixer from spurious responses. The mixer, a harmonic type, uses a millimeter-wave harmonic of the existing microwave LO in the analyzer. The conversion loss of such a harmonic mixer exceeds that of the fundamental harmonic mixer shown in Fig. la, but the design effort goes into the preselec tor, which is a passive component and therefore somewhat easier to design than a millimeter-wave LO. (Of course, once the resonators for such a preselector are available, a wideband oscillator may be possible if the active devices can be obtained.)

Fig. 1 . Three types of RF sections for extending the frequency range of a spectrum analyzer. The letters A, B, C, and D refer to Fig. 2, which shows where these RF sections connect to the spectrum analyzer, (a) The superheterodyne RF section uses a swept preselector and a swept local oscillator (LO). The phase-locked loop is used to set the beginning of the LO sweep accurately, (b) The block down-converter has a fixed LO and a swept intermediate frequency (IF), (c) The harmonic mixer version of the superheterodyne RF section.

The method of Fig. Ic was chosen for the HP 11974 Series preselected mixers. Fig. 3 shows the HP 11974 block diagram. The RF signal that is to be down-converted to IF enters the waveguide flange of the tunable preselector shown in Fig. 3, then goes to the isolator and the HP 11970 Series harmonic mixer. Electromagnets in the preselector develop a magnetic field, which tunes the preselector. The scaling electronics transforms the tune ramp voltage of the spectrum analyzer into magnet current. The unbiased harmonic mixer was developed previ ously2 to extend spectrum analysis into the millimeterwave range. If used without a preselector, the mixer con verts the RF signal to an IF whenever an LO harmonic sweeps past the RF. However, the horizontal frequency scale is only calibrated for a single harmonic of the LO, the 14th for the V-band example shown in Fig. 4a. The desired response, the 14 + signal in Fig. 4a, appears as a result, as do several unwanted responses resulting, for example, from the 12th, 16th, and higher harmonics. In the spectrum shown in Fig. 4a, the RF input consists of several signals from the frequency comb of a multiplier with outputs every 5.1 GHz. The unpreselected harmonic mixer shows several unwanted responses to each comb

Harmonic Mixer n = 1,2,3,4

RF Input 2 to 26 GHz

LO

Sweep Ramp Generator

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Fig. 2. Microwave spectrum ana lyzer block diagram, showing inter face points (A, B, C, D) with the millimeter-wave RF sections shown in Fig. 1 .

IF Output (310 or 321 RF In . LO Input S (3 to 6 GHz)

Fig. 3. HP 11974 Series prese lected millimeter-wave RF section block diagram.

REF 0. 0 dB

UNPRESELECTED HARMONIC 14L

PRESELECTED HARMONIC 14L

START 50. 0 GHz RES BW 300 KHz

VBW 30 KH=

STOP 75. 0 GHz SWP 7. 50 o«s =

(b)

Fig. 4. ("aj X\n unpreselected spec trum analyzer sweep from 50 to 75 GHz for an input signal consist ing of comb lines from a multiplier. There are several unwanted re sponses to each comb line. The harmonic responses to the 51GHz comb line are labeled, (b) A preselected spectrum analyzer sweep for the same input signal. The multiple responses are elimi nated and the multiplier comb lines every 5. 1 GHz are clearly displayed.

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line, thereby producing many responses, most of which are unwanted and severely hamper measurements. The HP 11974 preselected mixers add a waveguide track ing preselector to the harmonic mixer. The resulting V-band display is shown in Fig. 4b. Here, only one response occurs for each of the five comb lines.

Magnet Pole

Magnetic Field Lines

Hexagonal Ferrite Filter Design

Having decided to design the HP 11974 Series by adding tunable bandpass filters as preselectors to the HP 11970 Series unpreselected harmonic mixers, we looked for the easiest way of doing things to make the best use of our resources. At the outset, we had decided to use doped hexagonal ferrite spheres as filter resonator elements. Their built-in frequency offset (see article, page 59) allowed us to employ existing YIG tuning magnet designs to cover waveguide bandwidths. Because the HP 11970 mixers have TE10 waveguide inputs, and because it seemed extremely difficult to reduce typical YIG filter loop coupling struc tures (Fig. 5) to the small sizes that would be required to make filters for the highest-frequency band (50 to 75 GHz), we decided to use TE10 waveguide as the transmission medium in our filter. The high-frequency (53 to 80 GHz) barium ferrite filter work done by Lemke and Hoppe3 served as a starting point for our filter design. Their two-sphere, iris-coupled filter used crossed input and output waveguides (Fig. 6) and produced RF magnetic fields in the two waveguides that were perpendicular to each other at the iris to reduce out-ofband leakage. A linear taper was used to reduce the height of the waveguide to allow a smaller gap between the magnet pole tips. A two-sphere filter was built in U band (40 to 60 GHz) to demonstrate the feasibility of the crossed waveguide filter approach.4 This filter had typical insertion loss of 4.5 dB, a 3-dB bandwidth of 325 MHz, and off-resonance iso lation greater than 30 dB. The spheres were aligned on beryllia rods, which were slipped into holders that allowed ±0.1 mm of sphere adjustment from side to side and up and down in relation to the iris. The sphere rods were inserted through the reduced-height sidewall of the waveguide so that it was possible to center the spheres exactly over the iris and to move them closer together or farther apart to change the sphere-to-sphere coupling. In Fig. 7, the response of this filter is shown centered at ap proximately 48.5 GHz and moved up by 4.5 dB so the off-resonance isolation can be read easily off the plot. The low-frequency side of the filter's response cuts off more quickly than the high-frequency side, and 650 MHz away from the peak of the passband the rejection is about RF In

Fig. 6. Two-sphere waveguide bandpass filter.

35 dB. The rejection of a filter 650 MHz away from the peak is important for preselection applications because the IFs used in the HP instruments are approximately 310 MHz and 321 MHz. An unpreselected mixer will display an image signal at the same amplitude as the true signal at two times the IF away from the true signal. Therefore, much of a filter's usefulness depends on its image rejection, which is a measure of how much this unwanted trace is suppressed. By adjusting the spheres farther apart or closer together, and by changing the iris diameter and the sphere size, the best compromise between filter insertion loss, image rejection, and off-resonance isolation can be achieved. Two-sphere filters were built in the other millimeterwave bands using the information obtained from the Uband filter and applying appropriate scaling factors. The results for insertion loss and off-resonance isolation for the family of two-sphere waveguide filters5 are shown in Figs. 8 and 9, respectively. The 3-dB bandwidths of these filters were 200 to 350 MHz. Although the insertion loss results were acceptable, the image rejection and off-resonance iso lation of these filters were not sufficient for instrument applications. The goal was then changed to design a filter with off-resonance isolation and image rejection greater than 55 dB. A literature search showed three-sphere and four-sphere

YIG Sphere

RF Out

50 Frequency (GHz)

Fig. 5. A single stage of a typical YIG filter.

Fig. 7. Two-sphere U-band filter response.

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O -r

10

20

30

40 50 60 % of Band

70

80

90

100

-70

4 0 5 0 6 0 % of Band

Fig. 8. Insertion loss of two-sphere filters.

waveguide filter designs, but none of them would give the required off-resonance isolation at millimeter-wave fre quencies. Our next design consisted of two of the above two-sphere filters under one set of magnet pole tips, con nected by a very short transverse waveguide (Fig. 10). This four-sphere filter configuration does not increase the mag net pole tip separation, but in theory should double (in dB) the insertion loss, off-resonance isolation, and image rejection of the two-sphere filters previously built. To simplify the mechanical design, sphere mounts were machined from low-dielectric-constant plastic and epoxied over the irises. Resonator spheres were then placed on the sphere mounts, aligned and epoxied in place (Fig. 10). This sphere mounting technique allows accurate measurement of the sphere separation after mounting to determine sphere-to-sphere coupling. The one significant difference that was expected in going to the four-sphere design was the possibility of the two irises and the short transverse guide (one wavelength long at approximately 80% of band) forming a coupled-cavity bandpass filter that might give a fixed-frequency spurious

90 100

Fig. 9. Off-resonance isolation of two-sphere filters.

response. When the first four-sphere filters were turned on, they gave the expected double (in dB) off-resonance isolation, insertion loss, and image rejection, as well as the cavity-mode response (Fig. 11). By narrowing the width of the input and output waveguides and moving the spheres off-center towards the center of the filter, the onewavelength cavity mode can be pushed 5 to 6 GHz above the top frequency in the band. The one-wavelength cavity mode can thus be eliminated by shortening the transverse guide. However, this brings the one-half-wavelength cavity mode in-band at about 15% of the band. The one-halfwavelength cavity mode is not as strong as the onewavelength mode, and can be suppressed very well (Fig. 12) by introduction of a distributed loss in the transverse guide to detune the cavity. This loss is effected by a thin sheet of Kapton (plastic) between the sides of the transverse guide and the iris plate to allow some energy to leak out. The Kapton sheet is shown in Fig. 13, which also shows the four-sphere filter assembly. Four-sphere filters using scandium-doped barium ferrites as resonators are presently being built in A, Q, U, and

Fig. 1 0. Four-sphere filter design.

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Frequency (GHz)

Fig. 11. First four-sphere filter response shows cavity mode resonance.

V bands. They typically have insertion loss of 8 to 12 dB, 3-dB bandwidth of 120 to 200 MHz, image rejection greater than 55 dB, and off-resonance isolation greater than 70 dB. These performance figures represent trade-offs that were made between the different parameters. For instance, by mounting the spheres closer together (top to bottom) a foursphere V-band filter was made having 4 to 6 dB insertion loss across the band. Unfortunately, because of the tighter sphere-to-sphere coupling, the filter skirts were wider and the image rejection was degraded.

cient to determine the millimeter-wave frequency to which the spectrum analyzer is tuned. This voltage is then con verted to a coil current that will tune the filter to the appro priate frequency. To provide the correct current to the filter, the frequencyversus-coil current characteristics of the filter must be taken into account. The frequency of the barium ferrite filters varies linearly with current, and a straight-line approxima tion is sufficient. For example, a V-band filter typically deviates from a straight-line tuning equation by no more than ±90 MHz over the entire range from 50 to 75 GHz. Small tuning nonlinearities are compensated by using the preselector peak function of the spectrum analyzer. This function provides a small offset to the tune voltage to peak the filter on the signal being measured. Because of the internal anisotropic field of the barium ferrite spheres, very little current is required to tune the filters to the lowest frequency of the band. For all four bands, from 26.5 GHz to 75 GHz, the coil current required at the lowest frequency is approximately 70 milliamperes. The filters then tune to higher frequencies at a rate of 60 to 70 GHz/ampere. As a result, the widest frequency bands require the most current. The A band, with a span of 13.5

Magnet Thermistor Assembly Input/Output Waveguide

Filter Drive Circuitry

For proper system operation, the barium ferrite filter must track the input frequency of the spectrum analyzer. The HP 11974 Series preselected mixer receives a tuneramp voltage from the spectrum analyzer that is propor tional to the frequency of the spectrum analyzer's first local oscillator. For any given band, assuming a certain harmonic number, mixing sense, and mixer IF, this voltage is suffi-

Iris Plate Barium Ferrite Resonator Spheres

Kapton Sheet

Ref 0.0 dB, 10.0 dB/ Transverse Waveguide

Magnetic Center Body

Magnet Frequency (GHz)

Fig. 12. Four-sphere filter response with cavity mode sup pression.

Fig. 13. Four-sphere filter assembly.

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GHz, typically requires 270 milliamperes of coil current to tune to 40 GHz. V band, with a span of 25 GHz. typically requires 425 milliamperes of coil current to tune to 75 GHz. Coil current is provided by a 50-volt power supply. The coil current flows through the filter coil, a transistor that controls the amount of current flow, and a 3.1O resistor that is used to monitor the current flow, as shown in Fig. 14. To minimize the temperature dependent tracking er rors, the 3. 1Ã1 resistor has a low temperature coefficient, 5 ppm/°C, as do resistors in other critical locations. The power supply was chosen to be 50 volts to accommodate the voltage drops across all of the above items. The capaci tor across the coil shunts unwanted high-frequency cur rents away from the coil. The Zener diode across the coil provides a discharge path for the coil at the end of a sweep, when the current through the transistor goes to zero. The effect of temperature on the filter's frequency is another consideration in filter tuning. Some filters, such as the Q-band filter, have very little frequency drift with temperature, while others, such as the V-band filter, are very sensitive to temperature. With a constant coil current, a V-band filter drifts at a rate of +11.4 MHz/°C. For a tem perature increase of 50°C, the center frequency of the filter would increase by nearly 600 MHz. Compensation for the temperature drift had to be considered because the 3-dB bandwidth of the filter is typically between 120 and 200 MHz, and this would mean that an input signal would no longer be within the passband of the filter. Temperature and Delay Compensation

Temperature drift is compensated by monitoring the tem perature at the filter and modifying the coil current. A thermistor network is used to monitor the temperature of the filter. The thermistor network consists of a thermistor composite composed of two thermistors encapsulated in epoxy and two linearizing resistors. The thermistor com

posite is located in the waveguide portion of the filter as sembly (Fig. 13) and tracks the temperature at the barium ferrite filter. The network has a temperature dependent resistance that is linear from 0 to 1 00°C. The thermistor net work is connected as the feedback portion of an amplifier that generates a voltage equivalent to the amount of filter frequency correction required. This voltage is then summed into the voltage that generates the filter coil current. Although the temperature compensation required varies from band to band, the filters of each band are very consis tent from unit to unit and across the frequency band. This consistency allows the correction to be based on tempera ture only. In the A and Q bands, the filter drifts lower in frequency with increasing temperature, while in the U and V bands, the filter drifts higher in frequency with increasing temperature. Fig. 15 shows the frequency tracking errors of a V-band filter at 0°C, 25°C, and 75°C with no temperature compen sation applied. The frequency tracking errors of the 25°C trace represent the deviations from a linear relationship between the filter coil current and the filter frequency. The spacing between the three traces represents the temperature drift of the filter with no temperature compensation ap plied. Fig. 16 shows the frequency tracking errors of the same V-band filter with the temperature compensation circuitry enabled. The remaining frequency tracking errors fall within a range approximately equal to the 3-dB bandwidth of the filter. The preselector peak function of the spectrum analyzer removes these errors at a particular frequency. In addition to temperature effects, compensation must be provided for the effect of filter tuning delay. When the spectrum analyzer sweeps at a fast rate, the filter, tuned by the current through a coil with inductance of about 0.8 henry, tends to lag behind. This effect is compensated by placing a differentiator in the HP 11974 tune voltage path.

Differential Amplifier Tune Voltage Error Indicator

High-Frequency Reference Voltage

Low-Frequency Reference Voltage

Spectrum Analyzer Dependent Gain and Offset

Adjustable Gain and Offset

Delay Compensation Capacitor

Tune In

3.1ÃÃ

Fig. 1 4. Simplified HP 11 974 filter drive circuitry.

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Filter Frequency (GHz)

Filter Frequency (GHz)

Fig. com 5. V-band filter tracking error without temperature com pensation.

Fig. 1 6. V-band filter tracking error with temperature compen sation.

At slow sweep rates, this circuit has no effect. At fast sweep rates, additional coil current is provided to help the filter keep up with the spectrum analyzer. With this compensa tion applied, the spectrum analyzer can be swept at a maximum sweep rate of 40 GHz/second.

of the spectrum analyzer. Each of the three spectrum analyzer families has a different definition for the tuning voltage provided. Because of this, the HP 11974 has switches that are used to identify the spectrum analyzer with which it is to be used. For each switch setting, a specific gain and offset are applied to the tune voltage so that the filter will be properly tuned. Another requirement for the tune voltage of the spectrum analyzer is that it have a variable offset summed in. The correct amount of offset to apply at any given frequency is determined by the preselector peak function. Before operating the HP 11974 with the spectrum analyzer for the first time, two potentiometer adjustments must be made. These adjustments match the tuning volt ages provided by the spectrum analyzer to the reference voltages in the HP 11974. After these adjustments are made, the preselector filter will track very well the input fre quency of the spectrum analyzer. The preselector peak function is used to eliminate the remaining frequency track ing errors at any given frequency. When executed, this function causes the spectrum analyzer to vary its tune volt age to the HP 11974 and monitor the signal level of the marked response on the screen. At the maximum response level, the filter has been peaked. The frequency range of the preselector peak function is proportional to the har monic number on which the mixer operates. For most of the analyzers, the preselector peak range is ±260 MHz in

Spectrum Analyzer Compatibility

The HP 11974 Series preselected mixers are designed to operate with three families of Hewlett-Packard spectrum analyzers: the HP 70000 modular spectrum analyzer family with the HP 70907B external mixer interface module, the rugged, portable spectrum analyzer family including the HP 8560A, HP 8561B, HP 8562A, and HP 8563A, and the HP 8566B, a high-performance R&D bench spectrum analyzer. Fig 17 shows the HP 11974 Series and the spec trum analyzers. Older models of these spectrum analyzer families can be made compatible by installing a retrofit kit. To be compatible with the HP 11974, the spectrum analyzer must meet certain requirements. First, the spec trum analyzer must have a first LO frequency range of 3 to 6 GHz at the proper power level. The nominal power level of the first LO output is +14.5 dBm to +16 dBm. Second, the first IF of the spectrum analyzer must be com patible with the HP 11974. Each spectrum analyzer men tioned above has a first IF of either 310.7 MHz or 321.4 MHz. Finally, the spectrum analyzer must provide a voltage output that is proportional to the frequency of the first LO

Fig. 17. HP 11974A/Q/U/V pre selected millimeter-wave RF sec tions with mainframe microwave spectrum analyzers (HP 8563A, HP 85668, HP 70000).

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11974V CALIBRATION SN: 3001A00104 17 Apr 1990 n= 14+ IF=321.4 MHz LO Power=16dBm

55

6 0 6 5 FREQUENCY (GHz)

70

75

Fig. RF 8. Conversion loss calibration chart is supplied with each RF section. The data is entered into the mainframe spectrum analyzer.

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A band and ±450 MHz in V band. Conversion loss data for each instrument is required to make accurate amplitude measurements. Each HP 11974 is shipped with a graph and a tabular listing of its conver sion loss as a function of frequency, as shown in Fig. 18. The conversion loss measurements are traceable to the United States National Institute of Standards and Technol ogy. Data from the conversion loss table can be entered into the spectrum analyzer so that amplitude readings will automatically be referenced to the input of the HP 11974. In addition to the conversion loss table and graph, a conver sion loss label is permanently attached to the HP 11974 for reference. Acknowledg ments

R&D team member Dick Beardsley designed all the crit ical mechanical parts and made them look simple. He also organized the R&D retreats at the salmon school locations off the Northern California coast. The product introduction team completed their work in record time and included Robert Charlton, George Zimenski, Ron Flatt, Mariko Hoy, Lonnie White, Jim Lusk, Tom Berto, Joe Wax, Rich Pope, Bob Fullmer, Dennis DeMaria, Rebbie Toledo, Karen Bigham, Mike Picha, Bernie Hoven, Joyce Wong, Dennie Yamaoko, and Kathy Sparks. Mike Dethlefsen, Ernie deMartini, Mike Brown, and Steve Flint designed the retrofit kits vital to the project. Marketing efforts were by Eric Brown and Dennis Handlon. Important early development work on the filter and test routines was performed by Jimmie Yarnel, Dennis Derickson, Matt Fowler, and Hiroshi Imiazumi. Summer intern Davie Zoneraich built the first version of the millimeter tracking generator test set. Our lab section management, Frank Angelo and Toni Coon, endured endless project reviews and kept us inspired. And then there is Frank David, who peeled the company's first layer from the millimeter onion a decade ago. References 1. R.A. Shaffer, "Promising Uses are Emerging for Millimeter Radio Signals," The Wail Street Journal, June 26, 1981, pg. 29. 2. R.J. Matreci and F. K. David, "Unbiased Subharmonic Mixers for Millimeter-Wave Spectrum Analyzers," IEEE MTT-S Interna tional Microwave Symposium Digest, 1983, pp. 130-132. 3. M. Lemke and W. Hoppe, "Hexaferrite Components — Tunability at mm-Waves," Proceedings of the Conference on Military Mi crowaves, London, 1980, pp. 95-100. 4. D. Nicholson, "A High Performance Hexagonal Ferrite Tunable Bandpass Filter for the 40-60 GHz Region," IEEE MTT-S Inter national Microwave Symposium Digest, 1985, pp. 229-232. 5. D. Fil "Ferrite Tuned Millimeter-Wave Bandpass Fil ters With High Off Resonance Isolation," IEEE MTT-S Interna tiona] Microwave Symposium Digest, 1988, pp. 867-870.

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Hexagonal Ferrites for Mi 1 1 ¡meter- Wave Applications Scandium-doped, M-phase barium ferrite has the necessary properties. Crystals are grown and spheres are processed and tested in-house. by Dean B. Nicholson Ferrite spheres are commonly used as resonator ele ments in magnetically tunable bandpass filters. At frequencies below approximately 30 GHz, yttrium iron garnet spheres (abbreviated YIG, chemical formula Y3Fe5O12) are used extensively in this role. At frequencies above about 30 GHz (the millimeter-wave region) problems become apparent with the magnetic components used to tune the YIG spheres. These problems include electromag net heating, tuning nonlinearities, and hysteresis. The tuning equation of a YIG sphere,1 applicable with Ha parallel to H0, is: f,r e s o n a n c e = (2.8 MHz/Oe)(H0 + Ha

(1)

where H0 is the applied dc magnetic field and Ha is the internal anisotropy field (70 Oe for YIG). Using this equa tion, the maximum usable frequency of a YIG sphere can be calculated to be about 64 GHz, assuming that the material used in the tuning magnet pole tip has the highest satura tion flux density available (approximately 23 kilogauss for a cobalt-iron alloy).2 The anisotropy field Ha can be thought of as a built-in magnetic field that acts along a crystal axis, or in some cases a crystal plane. When the anisotropy field is parallel to the applied field, it gives a frequency offset that reduces the applied dc magnetic field needed for reso nance at a given frequency. It was obvious that a new resonator material would be Ha=25.5 kOe

required to make tunable bandpass filters to serve as pre selectors for the HP 11970 Series harmonic mixers covering from A band (26.5 to 40 GHz) up to V band (50 to 75 GHz). Using equation 1, it can be seen that if ferrite materials similar to YIG but with higher Ha could be found, then it would be possible to build magnetically tunable bandpass filters that cover waveguide bands in the millimeter-wave region using moderate magnetic tuning fields (Fig. 1). A class of material with this property is the hexagonal ferrites.3 Properties of Hexagonal Ferrites

Hexagonal ferrites are so named because this class of materials has a hexagonal crystal lattice, which produces crystals that have distinctly hexagonal shapes (Fig. 2). The hexagonal ferrites have a large number of phases. Fig. 3 compares the parameters of the most important phases (there are many more!) to YIG parameters.4'5'6'7'8 The most useful hexagonal ferrites have a property called uniaxial anisotropy (Fig. 4), which means that the anisotropy field lies along only one axis, which is the C axis for the hexag onal crystal. Hexagonal ferrites are commonly referred to by their phase and composition. For example, M-phase barium ferrite is BaFe12O19. The minimum useful frequencies listed in Fig. 3 come from three constraints. First, with the anisotropy field aligned with the applied field, equation 1 shows that the lowest frequency of resonance is (2.8 MHz/Oe)(HJ with negligible applied field. Second, the magnetic dipoles in

H, -0.01 kOe

5

1 0 1 5 2 0 Applied DC Magnetic Field H,, (kOe)

Fig. 1 . Ferrite resonance frequency as a function of dc mag netic field for various values of the anisotropy field.

Fig. 2. Hexagonal ferrite crystals.

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Notes: 1. Sc and Al dopings can be varied continuously. 2. Y phase has planar anisotropy. fr = (2.8 MHz/Oe)(H0(H0+Ha))1/2 when the anisotropy plane is aligned with both dc and RF fields.

Fig. 3. Summary of hexagonal ferrite and YIG parameters.

a ferrite sphere with the applied magnetic field aligned with Ha will not all line up or "saturate" until a field of at least 4-77Ms/3 has been applied. Third, for very high-Qu (unloaded QJ ferrites at low frequencies, such as YIG, with fields between one and two times 47rMs/3, the effect known as coincidence limiting8 limits the amount of power that a ferrite device can handle to much less than 0 dBm. There fore, YIG spheres are generally used with applied fields above two times 4-n-Ms/3. For hexagonal-ferrite-spheretuned devices, this power-limiting effect has not been seen at power levels up to 20 dBm for our bandpass filter con figurations and thus should not present a problem for this application. As Fig. 5 shows, scandium and aluminum dopings can be varied arbitrarily in M-phase hexagonal ferrites to give the desired Ha.4 The scandium-doped M-phase barium fer rite will satisfy the frequency range requirements at the lower frequencies while the aluminum-doped M-phase strontium ferrite will satisfy the requirements at the higher frequencies. Although it is possible to dope M-phase barium ferrite with aluminum to raise its resonant fre quency and dope M-phase strontium ferrite with scandium to lower its resonant frequency, in general, the higher the doping level the more the Qu of the resonator is degraded. Therefore, dopants and materials are chosen so that the

Fig. 4. Uniaxial anisotropy in hexagonal ferrites.

least amount of dopant is used to cover a given frequency range. Other desirable properties of M-phase hexagonal ferrites are that they have high 47rMs/3 for good coupling to the RF fields, high Curie temperatures for low sensitivity to temperature change, and fairly high Qu.

Fig. 5. Anisotropy field changes with doping. Adapted with permission from reference 4.

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test capabilities were developed in-house.

Sphere Production and Test

Once the selection of the M-phase hexagonal f errites was made and it was found that crystals were unavailable com mercially, a crystal growth program was begun at the HP Microwave Technology Division. In the literature, hexag onal ferrite crystals are typically grown from a BaO/B2O3 flux using slow cooling. We used a slow cooling furnace with multiple small crucibles per run and free nucleation (no seed crystals) for quick optimization of charge compo sition and temperature profiles. Now that growth condi tions have been optimized, a single larger crucible is used for each growth run with a larger charge so that larger crystals can be grown. The total volume of liquid charge in the crucible at the start of crystal growth is approximately 320 ml. The total weight of crystals obtained from the growth is about 70 grams. The processing of hexagonal ferrites to spheres is concep tually very similar to YIG sphere processing. Because of the brittle nature of hexagonal ferrites, proprietary grinding and polishing techniques had to be developed to avoid chipping the sphere poles. In addition, a separate sphere testing system was developed to test the Qu of the hexagonal ferrite spheres, which must be tested at the millimeter wave frequencies at which they will be used. Summary

Because of their high magnetic anisotropy fields, spheres made of suitably doped M-phase hexagonal ferrites were chosen as resonator elements in magnetically tunable bandpass filters. These bandpass filters cover waveguide bands above 26.5 GHz and are used as preselectors in the HP 11974 Series of millimeter preselected RF sections. When no outside supplier of hexagonal ferrite spheres could be found, crystal growth and sphere processing and

Acknowledgments

I would like to acknowledge Frank Gary for developing the sphere grinding and polishing processes and assisting with crystal growth. Without his help the project would have been immeasurably more difficult. In addition, I would like to thank Jerry Gladstone for management sup port even when the success of the project seemed uncertain at best. References 1. B. Lax and K.J. Button, Microwave Ferrites and Ferrimagnetics, McGraw-Hill, 1962, pp. 164-165. 2. HipercoR 50 Specifications, Carpenter Technology Corpora tion. 3. G. Winkler and H. Dotsch, "Hexagonal Ferrites at Millimeter Wavelengths," Proceedings of the 9th European Microwave Con ference, 1979, pp. 13-22. 4. P. Roschmann, M. Lemke, W. Tolksdorf, and F. Welz, "Aniso tropy Fields and FMR Linewidth in Single-Crystal Al, Ga, and Sc Substituted Hexagonal Ferrites with M Structure," Materials Re search Buiietin, Vol. 19, February 1984, pp. 385-392. 5. W. Tolksdorf, "On the Preparation of Polycrystalline Zn2Ba2Fe12O22 Especially With Respect to Added Bi2O3," IEEE Transactions on Magnetics, Vol. MAG-2, no. 3, September 1966, pp. 472-473. 6. F.E. Reisch, R.W. Grant, and M.D. Lind, "Magnetically Tuned Zn2Z Filters for the 18-40 GHz Frequency Range," IEEE Transac tions on Magnetics, Vol. MAG-11, no. 5, September 1975, pp. 1256-1258. 7. G.P. Rodrigue, "Magnetic Materials for Millimeter Wave Appli cations," IEEE Transactions on Magnetics, September 1963, pp. 351-356. 8. J. Helszajn, YIG Resonators and Filters, John Wiley and Sons, 1985, pp. 101-102.

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HP DIS: A Development Tool for Factory-Floor Device Interfaces The HP Device Interface System provides a development facility that includes a high-level Protocol Specification Language, a testing facility, and a run-time facility for device interfaces that run in an HP-UX environment on HP 9000 computers. by Kent Fulton Garliepp, Irene Skupniewicz, John U. Frolich, and Kathleen A. Fulton EFFICIENT DEVELOPMENT OF INTERFACES be tween computers and factory-floor devices can be a serious challenge in factory automation projects.1 These factory-floor devices consist of programmable logic controllers (PLCs), robots, numerically controlled ma chines, gauges, scales, and other devices. The problem is that they may come from many manufacturers and may have different, proprietary interfaces. For a few major brands of programmable controllers, there are off-the-shelf communications packages that can be purchased. This solution has limited applicability if the needs vary from what is implemented in the package. If flexibility is needed, a customized interface can be written. At present, development of specific device inter faces is a time-consuming, exacting, and expensive process requiring a fairly high level of expertise. The process gen erally consists of characterizing the device's communica tion protocol and then writing, changing, or enhancing programs, subroutines, and test suites. This process is wellknown to all interface developers and creates a slow re sponse to market needs. In the long run, the use of communications standards, such as the Manufacturing Automation Protocol2 (MAP), will eliminate many of the device connectivity problems and the response to market needs will improve significant ly. In the meantime, many factory-floor devices exist and have long useful lives remaining. Many are simple devices, such as gauges with simple interfaces, that may never con form to a standard. To reduce the cost of developing customized interfaces for devices that need them and to shorten the time required for such efforts, tools are needed to simplify the develop ment and testing of the interfaces. This is the objective of the HP Device Interface System (HP DIS). HP DIS is a toolset that helps developers create and test interfaces between computer applications and RS-232-compatible factoryfloor devices in less time than before. The resulting inter faces run in an HP-UX environment on HP 9000 Series 300 or 800 computers. HP DIS offers three facilities to make the development and implementation of device interfaces more efficient. A development facility provides a high-level Protocol Specification Language3 for defining the communications logic. A testing facility provides a test generator, a test

exerciser, and a device simulator. A run-time facility exe cutes the protocol in real time. Fig. 1 shows a typical pro tocol development cycle and the use of the HP DIS toolset. HP DIS: the Tools Approach

A diagram of the HP DIS system is shown in Fig. 2. The three bubbles correspond to the above-mentioned three facilities provided by HP DIS. These allow the system de veloper to develop, test, and run device interfaces. The development facility is simply a compiler that gen erates a protocol interface. The protocol interface is an executable process that forms the central component of an

Standard Process

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Corresponding Steps Using HP DIS Understand application needs. Understand device communication protocol and message formats. Design protocol interface architecture, functionality, and modularity.

Write application calls to protocol interface. Create protocol interface using the Protocol Specification Language. Create tests using the HP-DIS test facility.

Execute tests using the HP-DIS test facility.

Define the configuration and execute the protocol interface modules.

Fig. 1 . The process of creating a device interface.

Step 1 : Describe the Interface

Executable Protocol Interfaces and State Tables

Represents an HP-UX Message Queue

Fig. 2. HP DIS facilities Fig. 4. Steps in protocol interface development using HP DIS.

HP DIS system. The input to the compiler is a description of the device protocol, written in Protocol Specification Language (PSL). PSL allows the user to describe a state graph and its associated state table in a high-level format (see "Finite State Machine," page 65). Other inputs to the development facility are subroutines that can be linked to the protocol interface. In HP DIS these are called action routines (see "Action Routines," page 69) . The run-time facility provides the execution environ ment for the protocol interfaces. When the protocol inter face runs, it communicates with ports, other protocol inter faces, and other C programs through HP-UX message queues. Using a description of the protocol interface's as sociated I/O ports, the run-time facility manages the ports, message queues, process startup, and process shutdown.

The development and run-time facilities also provide the following features: • A contributed library of example protocol interfaces, tutorial protocol interfaces, and other helpful tools • The ability to implement user-defined lookup tables 1 Eight-bit native language support • Access between multiple devices and multiple interfaces • The ability to add and delete protocol interfaces dynam ically in a running system. A diagram of the HP DIS testing facility is shown in Fig. 3. This facility consists of a test generator and a test exer ciser. The test generator takes the state table and creates test cases. The test cases are fed to the test exerciser, which executes each test case by sending messages to the protocol interface under test. The test exerciser attempts to achieve each state listed in the state table, for up to 100% coverage. Optional inputs to the test exerciser are user-written test cases. The test exerciser executes a sequence of test cases and compares expected results to the results of the protocol interface under test. Actual devices or I/O ports are not necessary for testing; factory-floor devices can be simulated by describing their messages. The output of the testing facility includes test case documentation and test results. The testing facility also provides the following features: • Full or partial data tracing • Either menu-driven execution or script execution of test cases • Protocol filters to simulate garbled messages, time-outs, and expression matching • Notification of percentage covered.

Fig. 3. HP DIS testing facility.

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An HP DIS Example

There are three steps in developing an interface (see Fig. 4). The first step is to describe the interaction between the application and the factory-floor device interface. The sec ond step is to specify the device protocol in a language that HP DIS can compile. The third step after successful compilation is to generate the test scripts and test the logic of the developed interface. These steps are illustrated by the following example. Describing the Interface. A block diagram of the system interfaces for this example is shown in Fig. 5. The interface between the application and the device interface is an HPUX message queue. Read and write subroutines are avail able for the application program developer to send buffers to the device interface and receive buffers from it. These subroutines allow referencing either the HP-UX message queue name or the device application name. The links between the HP-UX message queues and the device inter face are established by the run-time facility through a con figuration file (Fig. 6). The configuration file is used by the run-time facility to establish the queues, start the defined interfaces, create the links, and configure the ports from the port definitions. The configuration process eliminates the need for a detailed understanding of HP-UX inter process communication and RS-232 serial port initializa tion. The buffers passed through the queues must be designed to carry the information needed by the device interface. The device interface can require the application to pass device-specific data directly or can translate generic func tions into device-specific data. Device interfaces can range from very device dependent to completely device indepen dent. In the latter case more logic will be required in the device interface.

For the sake of simplicity, this example uses the device dependent approach. The application outbound buffer con tains a six-byte header and a variable-length data string. The application inbound buffer contains a status byte and a variable-length data string. Specifying the Protocol. One of the methods of specifying the protocol is a transition diagram translated into a state diagram. This is particularly convenient for translating the protocol into a language HP DIS can compile. Figs. 7a and 7b describe a transition diagram and a state diagram for a nontrivial protocol. This example protocol is based on the Allen-Bradley Data Highway I protocol, but only exempli fies the major features. This example assumes synchronous communication. No new request is sent from the computer to the factory-floor device until a previous request is satis fied. The computer sends a message (MSG) to the device (Fig. 7a) and waits for an acknowledgment from the device (ACK). The computer then waits for a reply message (Fig. 7b). Each message consists of block control characters, a header, and data. In the case of a read request, the data field from the computer contains the address and the length of the re quest. The reply data from the device consists of the values requested. In the case of a write request, the data field from the computer contains the address and the values for the request. The reply data from the device consists of an inter nal status for the request. In the event of a communication failure, either the com puter or the device can reply with a failure message (NAK). The protocol interface must also recognize that no response (TO) is a failure. Other failure mechanisms are not taken into account in this example.

PLDEFINITIONS

F I F O Queues Q5

Runtime_Name Runtime_File_Name Runtime_Type

- Device_xx; = /users/test/Device_xx;

Runtime_Priority

= 51;

Port-Name

= AB;

= P;

PORT_DEFINITIONS

Factor-Floor Device Interface

Idle (Wait)

FIFO Queues Read Process

Write Process M I M ^ H B H

QUEUE_DEFINITIONS

7

â € ¢ ^ â € ¢ â € ¢ ^ ^ â € ¢ i

Queue_Name = Q2,Q3,Q4,Q5; QueueJJnk Q5> Device_xx; Device_xx > Q3; Q4> Device_xx; Device_xx
Factory-Floor Device

Fig. 5. System interfaces for HP DIS example. The queues are HP-UX message queues.

Fig. 6. Device interface configuration file.

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Finite State Machine The finite state machine model has been used in such diverse disciplines as computer design, neurophysiology, linguistics, au tomata theory, and communications.1 The finite state machine model is a natural way to describe systems that process signals. This model is particularly convenient for specifying how mes sages are processed in device protocols. Two standard representations used to describe a particular finite state machine are the state table and the state diagram.2 A state table uses one row for each state and one column for each input. In each box are written the next state and the output. The first row of the state table is usually assigned to the initial state of the machine. A state diagram is a directed graph in which each arc is labeled with is input that causes the transition and the output that is generated when the transition is triggered. A classic example is a parity checker. This machine takes an input stream of bits of ones and zeros. For each input bit the machine produces an output indicating whether the entire input sequence so far has even or odd parity. The state table and diagram are shown in Fig. 1. The HP DIS state table, written in PSL, is shown below. The initial, or home, state is have.even. When an event is triggered by the receipt of a 0 or 1 , the protocol interface prints a message using the user action routine called U1. Events zero_recd : response : 0; one_recd : response : 1 ;

State Table zero^recd

have_even

have_odd

State Diagram zero

zero reed, "print odd"

reed, "print even"

one

reed, "print even"

Fig. 1. Siafe table and state diagram for a parity checker.

States

References

have_even : Home;

1. P. and J. Dennis, and J. Qualitz, Machines, Languages, and Computation, Prentice-Hall, 1978. 2. A.S. 1988. Computer Networks, Second Edition, Prentice-Hall, 1988.

State.Table have_even : zerojecd : U1 ("print even") : have_even; have_even : one_recd : U1 ("print odd") : have_odd; have_odd : zero_recd : U1 ("print odd") : have_odd; have_odd : one_recd : U1 ("print even") : have_even;

Figs. 7a and 7b show state diagrams derived from the transition diagrams. The states and events form the logic of the protocol interface. Actions (or functions) are per formed at each state-event pair. Fig. 7 a also shows an event (retry exceeded) that is not supported by the transition diagram. This event is added to prevent endless looping, A message from the device to the computer (Fig. 7b) will cause a reply message event, which would normally return directly to the IDLE state. This example will check the integ rity of the byte stream by checking the BCC (block control

character) count and branching to an extra state (CHECK). If the BCC count was incorrect, the original message will be sent back to the device. If the BCC count was correct the message from the device will be returned to the appli cation. The combination of the IDLE state and the reply message event is included in case the device sends a mes sage after time-out processing. If this were not included, the wrong message would be extracted from the HP-UX message queue during the next transaction. The message from the device is simply acknowledged and ignored.

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State

Event

Transition Diagram

State Diagram

Table I Actions List

Computer Device

Actions

IDLE Send message Read message from application Build outgoing buffer from incoming buffer. Send message to device. Clear retry count. Increment message number. Start timer.

TO

Time-Out

Next

MSG

WAIT ACK AC K

Retry Exceeded MSG

IDLE Reply message

Read message from device. Send acknowledgment (ACK) to device.

IDLE TO = Time-Out or No Response

(a) WAIT ACK

Stop timer. Read message from device. Start timer.

WAIT

Stop timer. Read message from device. Resend message to device. Increment retry count. Start timer.

WAIT

Computer Device R e p l y

WAIT NAK

WAIT Reply message

Stop timer. Read message from device. Check block control character (BCC)

M e s s a g e

T i m e - O u t

TO MSG

ACK

CHECK

Reply Message

NAK

MSG

Stop timer. Send no response message to application.

WAIT

WAIT Retry exceeded

Stop timer. Send communications error message to application.

IDLE

CHECK Message OK

Send acknowledgment (ACK) to device. Send reply data to

IDLE

WAIT Time-out

Transition Diagram

State Diagram

TO = Time-Out or No Response

Fig. 7. Transition and state diagrams for a nontrivial protocol, (a) Message from computer to device, (b) Message from device to computer.

application. CHECK Message not OK

Send acknowledgment (NAK) to device. Increment retry count. Set timer.

WAIT

The state diagrams of Figs. 7a and 7b are combined into one state diagram in Fig. 8. The actions to be performed at each state transition are listed in Table I. With some additional declarations this table can be transformed into a Protocol Specification Lan guage (PSL) program that can be compiled. Previous deci sions about the form of the messages from the application can be incorporated into the data structures. Fig. 9 shows the PSL program ready for compiling and testing. The compiler not only checks the program syntax, but also tests the reachability of all states from/to the home (IDLE) state. This check ensures that there are no incomplete paths.

Reply Message

Send Message

Time-Out

ACK ) NAK

Reply Message

Message OK

Fig. 8. Protocol sfafe machine sfafe diagram obtained by combining F/gs. 7a and 7b.

66 HEWLETT-PACKARD JOURNAL OCTOBER 1990

© Copr. 1949-1998 Hewlett-Packard Co.

Matching Messages One of the most powerful features of HP DIS is the matching process. It ¡s used for three purposes: for determining whether a message matches a request event or a response event, for parsing a message into a structure, and for delimiting streams of characters from a port. Each use is slightly different from the others, but they all have the same matching characteristics. Through the PSL struct description, the user defines the fields in a structure that are to be matched. All variables describe a length of data. When a structure contains a variable, the data from the message ¡s placed into the structure according to the length of the variable. Byte and Boolean variables are one byte long. Integer variables are two bytes long, and real and long variables are four bytes long. String variables can be NULL or up to 4K bytes long. Data from the message is parsed into the structure's fields according to the variable lengths. Constants and literals are matched exactly. The lengths of data types are the same as above, but the message data must contain the bit pattern that matches the constant. Constants or literals adjacent to string variables are used for delimiting the strings. The HP DIS compiler builds a table for each structure describ ing data in each field. The matching process then walks this table a each structure. If there are no string variables in a structure, then each byte is easily assigned to a structure field. There is no ambiguity. However, if there are any string variables in the structure, then ambiguity branching begins, because string variables can be NULL or up to 4K bytes long. The matching process branches, assigning this byte to both the string variable

Testing. The tests, test scripts, and results files can be gen erated automatically at compile time with a PSL compiler option. The tests are executed from a test script and the results appear in several data files: • The action command file contains the test actions to be performed. • The comparison results file contains a summary of the test paths. • The trace data output file contains detailed test flows and variables. The test generator walks the state table and generates the actions command file (Fig. 10). The test generator starts with the first state-event pair in the PSL program and gen erates commands to trigger the event. The test terminates at the state and event in the ECASE statement (last state, next state, event of last state). The data following the WURA (write to upper-level read area) statement is the equivalent of a message from the application. The data following the WLRA (write to lower-level read area) statement is the equiv alent of a message from the device. A test case is generated for each subsequent state-event pair. The test cases (CASE 1 ; and CASE 2 marked Good and commented out in Fig. 10 were already successfully executed. Test cases three and four were created by a second pass of the test generator based on the previous tests. The test generator generates cases to trigger external events (messages from the application or device) by creat

and to the next field. This ambiguity is resolved either by the next constant or by the end of the message. HP DIS makes the first shortest match, unlike the HP-UX editor vi. which makes a first longest match. For example, if the fields in a structure are: variable string str! constant byte btl = B variable string str2

and the message received is: aabbBddBd

HP DIS uses a first shortest match algorithm to parse this as: strl = aabb bt1 = B str2 = ddBd

vi uses a first longest algorithm. The vi command typed in as: s/\(.*\)B\(A)/str1=\1 str2=2/

would result in strl and str2 matches as: str1=aabbBdd str2 =d

ing a message from the values involved. State-event pairs WAIT-ACK and WAIT-NAK (Fig. 9) were successfully generated because the test generator was able to use the structures ReplyAck and ReplyNak as the basis for triggering the events. The test generator generates cases for internal events based on the associated values of the constants or variables involved. If the values will satisfy the event, the case is generated. If not, the case cannot be generated. Each case is rechecked on every pass to see if the variables involved have been changed in previous test runs. For more complete automatic test coverage, the PSL program variables can be set to values favorable for test case generation. In some cases, the contents of the messages in the actions command file must be altered to affect subsequent cases. The test exerciser (Fig. 11) starts the interface under con trol file the run-time facility using the test configuration file (Fig. 12) and executes the test actions. At the conclusion of the test, the interface is terminated and the results are stored for examination. Fig. 13 shows the comparison results file. The expected state-event pairs for the expected results and the actual results are always shown. If the actual results differ from the expected results, the trace data output file (Fig. 14) can be examined to determine the cause. The trace data output file contains a detailed description of the data flow through the state table for each case executed by the test exerciser. It shows all incoming

OCTOBER 1990 HEWLETT-PACKARD JOURNAL 67

© Copr. 1949-1998 Hewlett-Packard Co.

Statejable

/ / / /

Max number of retries Time-out return status Device identifer Retry exceeded

/• Message sent OK; TimeOutVal

Variables byte

/" return status /' TO value = 1 s; / test = 30s

= 30000 /'1000'/;

RetryCount

= 0;

byte byte byte

bcc; status dst

/• Retry counter / Protocol block check character */

= 0; = 10;

/ P r o t o c o l s t a t u s * / / Protocol destination device */

byte byte byte integer string

src cmd sts tns data

= = = =

/ / / / /

0; 0; 0; 1;

byte boolean long string

Result; = TRUE; BccFlag TimePeriod = 0; Text / structures used to match messages */ struct ReplyAck = (OLE ACK);

Protocol source device */ P r o t o c o l c o m m a n d * t " P r o t o c o l s t a t u s * / Protocol message number */ â € ¢ D a t a b l o c k V

r Dummy for DcIO / Function for BCC check */ / " T i m e r v a l u e / â € ¢ B i t b u c k e t

struct ReplyNak =

(OLE NAK);

struct DataPacket = struct ReqPacket = struct ReplyPacket =

(OLE STX dst src cmd sts tns data OLE ETX bcc); (dstcmddata); (status data);

Events /" Event: Event Type, Event definition send_message: request, ReqPacket; reply_message: response, DataPacket; ACK: response, ReplyAck; N A K : r e s p o n s e timeout: internal, retry_exceeded: internal, msg_ok: internal, msg__nok: internal, States I D L E :

H O M E ;

ReplyNak; TimePeriod >= TimeOutVal; RetryCount>= MaxRetry; BccFlag = = TRUE; BccFlag = = FALSE; /" Home state */

V V

IDLE: sendjnessage: DclO(Read, Applic_read_Q, ReqPacket, , , Result)/ / START Build outgoing buffer 'I DcMove(ReqPacket.dst, DataPacket.dst)/ DcMove(HP_id, DataPacket.src)/ DcMove(ReqPacket.cmd, DataPacket.cmd)/ DcMove(StatusOK, DataPacket.sts)/ DcMove(tns, DataPacket.tns)/ DcMove(ReqPacket.data, DataPacket.data)/ DcCksum(Calculate, DataPacket.data, "BCC_AB", DataPacket.bcc)/ /' END Build outgoing buffer V DclO(Write, Devlce_Write_Q, DataPacket, , , Result)/ DcMove(0, RetryCount)/ DcCntrflncrement, tns, By_one)/ DcClock(StarLtlmer, TimePeriod, TimeOutVal) :WAIT; IDLE: reply_message: DclO(Read, Devicejead_Q, Text, , , Result)/ DclO(Write, Device_Write_Q, ReplyAck, , , Result) :IDLE; WAIT: ACK: DcClock(Stop_timer, TimePeriod)/ DclO(Read, Device_read_Q, Text, , , Result)/ DcClock(StarLtimer, TimePeriod, TimeOutVal) :WAIT; WAIT: NAK: DcClock(StopJlmer, TimePeriod)/ DclO(Read, Devicejead^Q, Text, , , Result)/ DclO(Write, Device_Write_Q, DataPacket, , , Result)/ DcCntr(lncrement, RetryCount, By_one)/ DcClock(Start_tlmer, TimePeriod, TimeOutVal) :WAIT; WAIT: replyjnessage: DcClock(Stop_timer, TimePeriod)/ DclOfRead, Device_read_Q, DataPacket, , , Result)/ DcCksum(Check, DataPacket.dst, "BCC_AB", DataPacket.bcc, BccFlag) :CHECK; WAIT: timeout: DcClock(Stop_timer, TimePeriod)/ DcMove(NoResponse, ReplyPacket.status)/ DclO(Write, Applic_write_Q, ReplyPacket, , , Result) :IDLE; WAIT: retry^exceeded: DcClock(Stop_timer, TimePeriod)/ DcMove(ComError, ReplyPacket.status)/ DclO(Write, Applic_write_Q, ReplyPacket, , , Result) :IDLE; CHECK: msg_ok: DclO(Write, Device_Writeja, ReplyAck, , , Result)/ DcMove(StatusOK, ReplyPacket.status)/ DcMove(DataPacket.data, ReplyPacket.data)/ DclOfWrite, Applic_write_Q, ReplyPacket, , , Result) :IDLE; CHECK: msg_nok: DclO(Write, Device_Write_Q, ReplyNak, , , Result)/ DcCntr(lncrement, RetryCount, By_one)/ DcClock(Start_timer, TimePeriod, TimeOutVal) :WAIT;

Fig. 9. PSL (Protocol Specification Language) protocol program.

68 HEWLETT-PACKARD JOURNAL OCTOBER 1990

© Copr. 1949-1998 Hewlett-Packard Co.

Action Routines HP DIS is shipped with a wide variety of routines to ease the creation of protocol interfaces. If a required action routine cannot be found in the HP DIS action routine library, the user can write a user action routine. A protocol interface consists of two components: a finite state machine and its corresponding internal tables. The finite state machine is customized for the HP DIS and user action routines. The internal tables are: 1) an identifier table consisting of con stants and variables, 2) an event table consisting of event IDs and event expressions, and 3) a state table consisting of current state ID, event ID, action list, and next state ID tuples. In the state table, the action list specifies HP DIS action routines or user action routines. Action routines operate on the variables in the identifier table. HP DIS provides a header file, DcTypes.h, which can be used by user action routines written in the C pro gramming language to simplify parameter passing. The HP DIS-supplied action routines are listed below. DcBufMod DcCksum DcClock DcCntr DcConvert DcDelay DcEncode DcExit DcFlag DcIO DcLogAdJVB DcMove DcScan DcTablnit

Buffer modification Checksumming Timer Counter Data conversion Delay Data encoding Terminating the protocol interface Flag setting Input/output Address builder Move Data scanning Table initialization

messages, state-event pairs, and values of all variables after every action associated with each state-event pair. The vari able values are useful for checking the results of actions even when the correct path is executed. This example has shown that by using tools and a subsys tem approach, a factory-floor device protocol can be mod eled and produced. Configurations

Fig. 15 shows various configurations for HP DIS-built interfaces. Interface schemes can use a single protocol in terface or multiple protocol interfaces. These protocol in terfaces can be stacked in series or configured in parallel. When multiple devices are serviced, even more choices can be made: each device can be serviced by its own dedi cated protocol interface, or multiple devices can be ser viced by a generalized protocol interface. Fig. 15a shows the simplest configuration. Here, one pro tocol interface handles one port and one device. Fig. 15b shows three protocol interfaces that work to gether. Message processing that is common to all ports is done in the lower-level PIl. The message is passed to the upper-level PI2 and PI3 for device-specific processing. For example, PIl can collect all messages from multiple de-

Table scanning Buffer modification

DcTabScan DcBufMod

An Example The HP DIS action routine DcClock activates or deactivates a time HP facility. Timer counters are caller-supplied HP DIS variables. The HP-UX system interval timer ITIMEFLREAL is used to update the time counters in real time. A SIGALRM signal is delivered when the system interval timer ITIMEFLREAL expires, and all active timer counters are updated. Updating a time counter can trigger an event if the timer counter exceeds a specified time-out value. In the following example the event TimeOut is triggered when time_counter is greater than 60000 (60 sec onds). Variables long time_counter; Events TimeOut : internal, time_counter > 60000; StateJTable

DcClock(1 , time_counter, 1 000)

/ Starttimecounting */

Idle: TimeOut: DcClock(2, time_counter)

/ Time-out detected */ / Stop time counting */

/ Time_Stamp: 608506312 */ / R u n - T i m e N a m e Runtime.Name Deviceja / CASE1; V /' Good '/ / S t a t e C o m m a n d / '

I D L E

W U R A

State Table File Name */ /users/test/Devicejix.st;

' /

\ 0 1 2 V O O O ' ;

* /

/" End of case '/ /• ECASE IDLE WAIT sendjnessage; */ /• CASE 2; '/ /• Good */ /• state Command 7 -/• IDLE WLRA '020002012000000000000 */ / â € ¢ 0 0 1 0 2 0 0 0 3 0 0 0 ' ; 7 / End of case 7 / ECASE IDLE IDLE replyjnessage; 7 CASE 3; / " S t a t e C o m m a n d * / I D L E W U R A ' \ 0 1 2 \ 0 0 0 1 ; W A I T W L R A / End of case 7 ECASE WAIT WAIT ACK; CASE 4; / S t a t e C o m m a n d 7 I D L E W U R A ' 0 1 2 0 0 0 ' ; W A I T W L R A \ 0 2 0 \ 0 2 5 ' ; /" End of case 7 ECASE WAIT WAIT NAK;

Fig. 10. Action command file.

OCTOBER 1990 HEWLETT-PACKARD JOURNAL 69

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Runtime_Name: Device_xx

Test Exerciser

Execution_Number: 1 Case_Number: 1 Status: Cases identical in file Devicejcx.tr and file Device j
Q5 HP-UX Message Queues

m

Q1

Q4

Factory-Floor Device Interface

Device Simulator

MP-UX Message Queues

Event Path taken and Case Status in file Device_xx.tr: [ I D L E : s e n d _ m e s s a g e D C M O V E Case.Status: 0 Event Path taken and Case Status in file Devicejcx.da: [ I D L E : s e n d _ m e s s a g e D C M O V E Case.Status: 0

,

D

C

I

O

,

D

C

I

O

Execution_Number: 1 Case_Number: 2 Status: Cases identical in file Devicejcx.tr and file Device_xx.da

Fig. 1 1 . Testing interfaces.

Event Path taken and Case Status in file Device_xx.tr: [IDLE:reply_message,DCIO;DCIO;IDLE] Case_Status: 0

vices, perform checksums, and pass them to the next level. This ensures that all messages are acknowledged promptly by a dedicated protocol interface, while less time-critical functions are handled by separate protocol interfaces. Fig. 15c shows three protocol interfaces, each dedicated to a port. Device-specific message processing is done for each port. The upper-level PI4 directs and organizes mes sages before passing them up to the application. A developer can choose where to put common functions. The performance will be slightly better when the number of protocol interfaces in serial is smaller, since fewer mes sages are passed between processes. On the other hand, a centralized function may be desirable because it simplifies the system design. Performance

An HP DIS system is easier to construct than a similar application in C code, but this is achieved with some loss of performance compared to C code. In an HP DIS system, functionality is split across five (or more) separate HP-UX processes. In C code, all the functionality could reside in a single process. For example, HP DIS port management is handled by separate read and write port processes with

PLDEFINITIONS Runtime^Name = Devicejoc; Runtime_Type - T; Runtime_Name = PMDPSS; Runtime_File_Name = /usr/bin/PMDPSS; /* Device Simulator '/ Runtime.Type = T; QUEUE_DEFINITIONS Queue_Name = Q1,Q2,Q3,Q4,Q5; Queue.Link Q5 > Device_xx; Device_xx > Q3; Q4 < Device_xx; Device_xx < Q2; PMDPSS < Q3; PMDPSS > Q2; Q1 > PMDPSS;

Event Path taken and Case Status in file Device_xx.da: [IDLE:reply_message,DCIO;DCIO;IDLE] Case_Status: 0

Fig. 13. Comparison results file.

Execution_Number: 1 Case_Number: 1 Runtime.Name: Device_xx Trace_Data_Available Act¡on_Command: WURA ProtocoLMessage_Transmission_Elapsed_Time: Thu Apr 13 14:33:30 1989 ProtocoLMessage_Data_Packet: '\000\012\000 ' Status: Triggered State: IDLE Event: send.message Variable_RetrievaLEIapsed_Time: Thu Apr 13 14:33:30 1989 State_Table_ Variables: ReplyPacket.data = ' ' ReplyPacket.status = 0 ReqPacket.data = ' ' ReqPacket.cmd = 0 ReqPacket.dst = 10 DataPacket.bcc = 0 DataPacket.data = ' ' DataPacket.tns = 1 DataPacket.sts = 0 DataPacket.cmd = 0 DataPacket.src = 0 DataPacket.dst = 10 Text = ' ' TimePeriod = 0 BccFlag - True Result = 0 data = ' ' tns = 1 sts = 0 cmd = 0 src = 0 dst = 10 status = 0 bcc = 0 SYS_ERR = 0 Status: Triggered State: IDLE Event: send.message Action: DCIO Variable_Retrieval_Elapsed_Time: Thu Apr 13 14:33:30 1989 State_Table_Variables: ReplyPacket.data = ' ' ReplyPacket.status = 0

Fig. 12. Test configuration file.

Fig. 14. Trace data output file.

70 HEWLETT-PACKARD JOURNAL OCTOBER 1990

© Copr. 1949-1998 Hewlett-Packard Co.

process will be preempted. HP DIS uses this HP-UX exten sion. With real-time HP DIS processes, response time vari ability can be decreased.

(a)

Application^» Application

Performance Test Results

HP DIS performance studies were conducted to answer these questions: • What is the performance on HP 9000 Series 300 and Series 800 computers? • What is the throughput of an HP DIS interface? The flexibility of HP DIS allows device interface modules to be configured and combined in an infinite number of ways. A simple model was chosen that gives representative data involving the major items contributing to performance. Fig. 16 depicts a typical configuration. An application (PModel) is connected to a device interface module (PIl), which is connected to an HP-UX RS-232 multiplexer port. The port has a physical loopback connection and all data written to the port is immediately read back from the port. Each port has one PModel. A fixed-length message is sent to the port by a PModel and returned unchanged. Because the application program waits for each message to return before sending another, only one message is in the loop at a time per PModel. Throughput data is averaged over 20 transmissions for various message lengths using one, then

6-Channel Multiplexer

Fig. 15. Configurations for HP DIS-built interfaces, (a) One protocol interface handles one port and one device, (b) Three protocol interfaces work together, (c) Three protocol inter faces, each dedicated to a port, with an upper-level interface (PI4) directing and organizing messages.

3000

connected HP-UX message queues. HP DIS handles the message buffering. This decreases development time since port configuration and buffer management code does not have to be written. However, the performance of this port interface will fall short of a similar interface with integrated port management functions. It is also relevant that HP DIS is an HP-UX application. An HP-UX cell controller, whether written in HP DIS or in C, is subject to normal HP-UX timesharing policies, and will have nondeterministic response times. With HP-UX on HP 9000 Series 800 computers, processes can be run under a real-time priority to decrease the chance that a

2 Ports

1 Port

1 0 0 0

3000

2 0 0 0

Message Length (Bytes)

2 Ports

1 Port

Multiplexer

(b)

Loopback Ports -

Fig. 16. HP DIS performance test model for multiple ports. PModel is a simulated HP DIS application.

1 0 0 0 2 0 0 0 Message Length (Bytes)

3000

Fig. 1 7. Loopback response time for performance tests using the HP DIS application PModel on (a) HP 9000 Model 375 and (b) HP 9000 Model 832 computers (HP DIS 2.2 on HP-UX 7.0).

OCTOBER 1990 HEWLETT-PACKARD JOURNAL 71

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two PModels. Fig. 17 shows the data throughput of an HP 9000 Model 375 and an HP 9000 Model 832, both with 16M bytes of memory, under the HP-UX 7.0 operating system. The throughput in Fig. 17 reflects the transfer of data one-way. The curves show the data throughput for one PModel and the sum of the data throughputs for two PModels. The throughput decreases with message sizes above 1000 to 1500 bytes because HP DIS is performing message match ing (see "Matching Messages," page 67). HP DIS matches raw byte streams to the user's definition of the message. Summary

The Hewlett-Packard Device Interface System, HP DIS, is a tool that eases the development of communication links between computers and factory-floor devices. Inter faces can be developed more quickly than with conven tional code. Devices can be simulated, and testing is mostly automated. Communication links can be scaled, using only the routines needed for the application at hand. Through the use of this tool , factory-floor devices from many vendors can be mixed and matched. HP DIS can improve productivity, reliability, develop ment costs, and market response and reduce support costs for device interfaces.

Acknowledgments

HP DIS was made possible by the teamwork and dedica tion of many people, especially the R&D team. The authors would like to acknowledge the other present team mem bers — Frank Leong and Marve Watkins — and Ron Becker, the project manager, who pulled it all together. We also would like to acknowledge previous team members — Cle men Jue for the development environment, David Brunstein and Tom Hirata for the testing environment, and Wes Higaki who was one of the initial investigators. Dan Shive and Ron Short of the technical support group made the manuals a reality. The authors also acknowledge all the contractors, technical writers, marketing people, and man agers without whom HP DIS could not exist. References 1. F. Litman, "Software Tools for Plant-Floor Connectivity, "Auto mation, Vol. 35, no. 4, April 1988, p. 28. 2. Hewlett-Packard Journal, August 1990, pp. 6-60. 3. C. Jue, "A System to Develop Factory Floor Device Interfaces," Proceedings of the Third International IMS Conference, Vol. 3, part 1, September 1987, pp. 134-146.

72 HEWLETT-PACKARD JOURNAL OCTOBER 1990

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Measurement of R, L, and C Parameters in VLSI Packages Developed to verify the electrical models of a 408-lead multilayer ceramic package, this measurement technique can measure the very small inductances, capacitances, and resistances that are typical of high-performance packages. It does not require extraction of RLC parameters from time-domain reflectometer measurements. by David W. Quint, Asad Aziz, Ravi Kaw, and Frank J. Perezalonso

THE NEED FOR HIGH-PERFORMANCE, high-pincount 1C packaging with a large number of I/O con nections has brought about a project to design and characterize a multilayer ceramic PGA {pin-grid array) ca pable of providing up to 320 I/O lines at an operational frequency in excess of 60 MHz. Our challenge is to produce a package that brings the performance advantages of mul tilayer cofired ceramic technology to high-lead-count, highpower VLSI circuits. The package currently in development will mount a 14-mm-square CMOS chip. Fig. 1 is a cross-sectional drawing of the package. The package contains 12 metallization layers, which are used for signal, power, and ground routing, and uses three-tier bonding from the chip to the bonding pads on the package. The top two bonding tiers on the package are exclusively for signal or I/O connections. The bottom bonding tier is reserved for power supply and ground connections. The signal routing layers provide a stripline environment and there is a ground plane adjacent to each of the power supply planes. The pads on the chip are spaced at an effective pitch of approximately 110 micrometers (0.00433 inch). We have been able to match this pitch on the package by using two signal bonding tiers. Power supply connections are divided into eight groups for flexibility and noise isolation. The

chip mounts directly on a copper-tungsten heat spreader that is used for heat dissipation. The heat spreader is also connected to ground. Electrical Modeling

The designers of system processing units put considera ble effort into system simulations. One of their main con cerns is the amount of noise induced on logic VDD (logic VDD powers the internal circuitry of the 1C) and logic GND (ground). Another concern is noise on signal lines. Noise is caused by power and ground bounce and by coupling of signals from one line to another. The main source of this noise is the familiar Ldi/dt term, which arises from logic and I/O driver currents flowing in the inductance of the package and circuit board conductors. To produce mean ingful simulations, it is necessary to include models of all these components in the circuits. The simulations are par ticularly sensitive to the 1C package model, since the pack age lead inductance accounts for most of the inductance L in the Ldi/dt term for computing power supply bounce. The values of the power supply inductances that need to be added in the simulations range from about 70 picohenries to about 0.5 nanohenry. In addition, ground models ""Bounce" in grojnd and power supplies refers to a temporary droop or rise in the supply voltage caused by large currents drawn by devices using the supplies-

Bottom Bonding Tier Middle Bonding Tier Top Bonding Tier

Dielectric Layer 1 Dielectric Layer 2 Dielectric Layer 3 Dielectric Layer 4 Dielectric Layer 5 Dielectric Layer 6 Dielectric Layer 7 Dielectric Layer 8 Dielectric Layer 9 Dielectric Layer 10 Dielectric Layer 11

(TL-1) (TL-2) (TL-3) (TL-4) (TL-5) (TL-6) (TL-7) (TL-8) (TL-9) (TL-10) (TL-11) Bypass Capacitor

Bypass Capacitor

Fig. 1 . PGA (pin-grid array) con struction detail (not to scale). All dielectric layers are 0.008 inch thick.

OCTOBER 1990 HEWLETT-PACKARD JOURNAL 73

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and signal trace models including cross coupling need to be included in the system simulations. Model Verification

Creation of electrical models for the PGA was facilitated by various software tools and by leveraging previous work done on the subject. Verifying that these models were cor rect was much more challenging and is the main topic of this paper. Models were verified by comparing package parameters calculated from the models with measurements on an actual PGA package. Most high-frequency measurements are done using a net work analyzer or a time-domain reflectometer (TDK). Both instruments measure reflections from discontinuities. The problem with using a TDK lies in the interpretation of the results when the time delay through a discontinuity is short compared with the rise time of the propagating pulse. The PGA package signal leads consist of stripline transmission lines with a signal propagation time between 100 and 200 picoseconds and a characteristic impedance of approxi mately 37 ohms. Considering the time delay through the package, a TDK pulse with a rise time of about 20 pico seconds is necessary to give good resolution. Using such a fast rise time, skin effect, dielectric losses, and reflections from the test fixture and interconnections distort the reflec tion test signals to such a degree that it is virtually impos sible to extract an RLC circuit for the package itself. A TDR measurement also does not give numbers for first-order and second-order mutual inductances and capacitances be tween signal lines. TDRs are especially unsuitable for the power supply planes because of the extremely low charac teristic impedances of these planes (5Ã1 or less). A TDR does not have the ability to drive such a low-impedance load. Since simulations are done with the HP Spice software package using models made up of discrete R, L, and C elements, these are the parameters that need to be verified. Because TDR or direct measurements with an impedance analyzer cannot give this kind of detail, it was deemed necessary to develop another measurement technique, which is described in the following sections. Capacitance Measurement

A typical PGA signal trace structure, including the signal wirebond and the PGA pin, is modeled in the passive cir cuit of Fig. 2. This is a useful model for HP Spice simula tions. It can also be approximated in the form of transmis Wirebond

sion lines with Z0 = VE^7c7 and propagation time t = VLjCj. The transmission line approach is more dif ficult to apply when the mutual coupling and resistive losses are important. This is the case in any 1C package where a number of I/O lines and internal circuits are switching simultaneously. The RLC equivalent is applica ble to any circuit where the time delay of the element is less than about half the shortest rise time of the propagating signal. In the case of pin-grid array packages, the odd geometry gives the device non-TEM properties; for exam ple, the capacitive and inductive coupling coefficients are not equal. To overcome the shortcomings of traditional measure ment techniques, the following method is used. The R, L, and C values in Fig. 2 are measured using slightly different electrical circuits. The only source used is a ramp generator and the only detector used is an oscilloscope with a matched 50Ã1 input impedance. Fig. 3 illustrates the mea surement of a capacitance such as the coupling capacitance between the two traces. The use of a ramped input signal cancels effects of circuit elements that are not under test and aids in the interpretation of results. The charging cur rent i(t) defines the voltage across the oscilloscope's chan nel 2 inputs and the unknown capacitance Cx can be calcu lated from = Vmax/(Rscope2dVin/dt)

(1)

where voltage is measured at the center time of the Vgen ramp. The voltage Vou, is small, but its accurate measurement is important to the determination of the parameter values. The measurements that must be taken on the oscilloscope screen are the slope of the Vin ramp (dVin/dt) and Vmax, the plateau voltage on Vout. Matched coaxial cables be tween the instruments and the device under test introduce time delays, but do not introduce any additional factors in the equation for Cx above. For example, losses in the coaxial cables from the sample to the oscilloscope will introduce no error if they are the same length for both channels, since the measurement depends on the quotient of the measured voltages. The voltage drops across the series resistance and inductance in the trace are small, since they are in series with the capacitive impedance. The capacitive impedance dominates the current, so the resistive and inductive volt-

PGA Trace

PGA 3.2 nH 50 mil Pad Node T1

0.30 pF

Node T4

GND 3

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Fig. 2. Passive circuit model of a typical PGA signal trace structure, showing typical trace parameters. Nodes T3 and T4 are correspond ing nodes on the adjacent signal trace for capacitive coupling. In ductive coupling is not included in this model.

ages can be ignored. In addition, the capacitive loading on the Vout side is of little consequence, because the voltage being measured (the plateau top) is essentially constant. The capacitance on the Vout side will drop out of the mea surement equation if the time constant Cou,RSCOpe2 is much less than the test pulse rise time. Cx can be measured quite easily at several pulse rise times, and the calculated values of Cx can be compared for the different measurements. The longest pulses will give smaller plateau voltages, increasing the importance of the signal-to-noise ratio of the equipment, while the shorter pulses will cause the measurement to depart from its true value in a systematic way as the parasitics in the test jig become more dominant. In the PGA and other common packages, there is usually a wide range of pulse rise times that give the same answer for the value of the tested ele ment. In this and all the other test situations, the test jig param eters must be measured without the package and subtracted from the values obtained with the package in place. The design of the test jig is important and must include matched-impedance lines with connections as close as pos sible to the PGA to minimize the parasitics of the test jig. Good ground integrity is important, since large parasitics can be introduced quite easily. Poor connections are easily found using the real-time display of the oscilloscope. Move ment of a poor connection will produce corresponding wiggling of the oscilloscope trace and a poor connection can usually be located quickly and corrected. Once the test jig and cabling are connected properly, movement of the cables should produce no noticeable movement of the os cilloscope traces. This troubleshooting ability is another benefit of this technique.

The input impedance of the signal trace, represented by Lx in series with Rx, is low compared with the effective source impedance of the generator and the oscilloscope in parallel (RgeJRscope). so the inPut current is determined solely by the test equipment connected to the circuit. Thus, current I(t) = Vgen(t)/Rgen, since the package under test is virtually a short circuit. Virtually all of the current from the ramp generator flows through the package trace, so the voltage Vout is determined solely by the trace inductance and resistance. Again, if the rise time of Vgen is much greater than the time constant of the generator and package induc tance, the voltage across the package quickly becomes Voul = Lxdl/dt + RXI. The output pulse consists of the sum of two components: (1) a flat-topped pulse like the one in the capacitance measurement, and (2) a ramp proportional to the input current. If we separate the two voltages in Fig. 4, call the inductive voltage Vlx, represented by the plateau voltage, and call the resistive voltage Vrx, the final voltages after the ramp can be found from:

Inductance Measurement

For each of the parameters that we measured (inductance, capacitance, mutual inductance, and mutual capacitance) we had to build a different set of probes. The parasitics of

Inductances are measured by applying ramped currents instead of ramped voltages to the traces under test. This is arranged by shorting the wirebonds of the PGA traces to the PGA ground circuit. This circuit is shown in Fig. 4.

(2)

Lx =

(3)

n/ *

where dVgen/dt is the slope of the ramp voltage and Vgenmax is the final voltage of the Vgen step (see Fig. 4). The bounce caused by the partial inductance of the PGA ground net can be canceled by driving a third (uncoupled) signal trace, grounded to the shield at the inner lead bond, with a negative-going ramp of the same magnitude. The third lead must be uncoupled so that mutual inductance does not contribute unwanted voltages to the measurement. Test Fixture and Parasitics

c, F U n R , c o p e ,

(Channel 1)

Time (ns)

Fig. 3. Capacitance measurement circuit and voltage wave forms.

Fig. 4. Inductance measurement circuit and voltage wave forms.

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these probes were zeroed out before and after each measure ment to make sure that the characteristics of the probes did not change during the measurements. This was espe cially important in the case of the power supply inductance measurements because the characteristics of the probes were comparable in magnitude to those of the package. Signal Models

Signal trace models were calculated using Stripcal1 to calculate the lumped elements in the trace model between the PGA bond pad and the base of the pin. Ind32 was used to calculate the inductances (both self and mutual) for the wirebonds. The measurements were done on a 408-pin PGA that had a test chip mounted and bonded in it. For the inductance measurements, all the wirebonds were shorted together on the chip. For the capacitance measure ments, all the signal wirebonds were isolated. Resistance measurements are not discussed in detail be cause they are straightforward and because the measured values of the tungsten metallization sheet resistance were between 5 and 7 milliohms/square, well below the maxi mum specification of 13 milliohms/square. In addition, the resistance of the ground and power supply routing was less than 5 milliohms, which was not considered signifi cant. The inductance measurement results were as follows:

Parameter SelfLofVDD Self L of VDL (group 1} Self L of VDL (group 2) SelfCofVDD Self C of VDL (group 1) Self C of VDL (group 2)

Measured Calculated Difference 97 pH 79 pH 19% 0.88nH 0 . 7 7 n H 1 4 % 1.18nH 1.06nH 11% 4.96nF 4.92 nF 1% 0.66 nF 0.62nF 6% 0.5 nF 0.47 nF 6%

Note: VDD is the logic power supply voltage and VDL is the I/O driver supply voltage. VDD Measurement Errors

In the VDD inductance measurements, the topology forced us to put all eight ground wirebonds on the same side of the VDD wirebonds instead of four on each side as the chips are actually bonded. Moving all the ground wirebonds to one side of the VDD wirebonds may increase the inductance of the wirebonds by up to 50%. This effect accounts for most of the difference between the calculated and measured values of the VDD inductance. Fig. 5 compares the measure ment bonding pattern and the pattern the package was designed to use in actual operation. Another source of error is the shape (loop height, length, etc.) of the wirebonds. The wirebond shape may be turn out to be different from the one that was analyzed.

Parameter Measured Calculated Difference Self L (upper tier) IS.lnH 15.2nH 1% Self L (middle tier) 14.9nH 14.6nH 2% Mutual L (middle tier) 3.64nH 3.21nH 12% Mutual L (upper tier) 4.7nH 4.5nH 4% WB coupling (1st order) 2.0nH 2.1nH 5% WB coupling (2nd order) 1.4nH 1.5nH 7%

n

Chip

4GND8Power4GND

Package

Note: WB = wirebond. The sources of error for the signal inductance parameters are: (1) the routing on the chip, (2) variations in the length and the shape of the wirebonds and traces, and (3) imper fections in the ground planes. The capacitance measurement results were as follows:

(a)

4 GND

Parameter Self C (upper tier) Self C (middle tier) Mutual C (upper tier) Mutual C (middle tier)

Measured Calculated Difference lO.lpF 9.5pF 6% 6.5pF 6.3pF 3% 0.7 pF O.SpF 29% O.GpF O.SpF 17%

The sources of error in the signal capacitance measure ments are: (1) the capacitance of the pin braze pads, and (2) the capacitance of the vias and the associated cover dots. The capacitance between the wirebonds and between the pins was found to be less than 0.1 pF and has been ignored. Power Supply Models

The measurements were done in the same way as for the signal traces. The results were as follows:

Chip

D Package

(b)

Fig. 5. To measure VDD inductance, it was necessary to put all eight GND wirebonds on the same side of the VDD wirebonds, as shown in (b). In actual service, the wirebond pattern is as shown in (a). This accounts for most of the difference between the measured and calculated values.

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VDL Measurement Errors

Acknowledgments

The wirebonding pattern may vary in the VDL bonds. In the calculations for the VDL inductance, we also did not take into account the inductance of the epoxy routing on the chip. The power trace capacitance measurements were done without the bypass capacitors because the 0.1-/xF nominal value of the bypass capacitor is very large compared to the capacitance parameter that we were trying to measure. A very high degree of correlation was obtained between mea surements and calculations.

References

Conclusions

It is important to be able to verify electrical models of packages used in high-performance systems. Time-domain reflectometry cannot give the kind of detail needed for model verification, and it is very difficult to derive an RLC circuit from the results. The measurement technique described in this paper3 overcomes the problems associated with TDR measure ments. Inductance is measured while capacitance is shorted out, and capacitance is measured on open-circuit traces so inductive effects are negligible. Slow rise times of input voltage pulses make it possible to avoid transmis sion line effects. A feature of this method is that the mea surements can be made with readily available digital oscil loscopes and pulse generators. Good correlation between the calculated and measured results for the PGA package was obtained. This measure ment technique has also been used to measure parameters of TAB [tape automated bonding) packages, printed circuit PGAs, and printed circuit board connectors with good re sults, and could also be useful in other electrical model verification experiments.

We would like to thank Ken Lee and Ralph Liu. who assisted with this effort and provided invaluable ideas and advice. We would also like to thank Bob Crawford and Ron Bernard for designing the probes and writing the software for the measurements, and Pauline Prather for her support and expertise in bonding and assembling the test devices. Colorado 1C Division assembly, particularly Dave Gilzean, helped wholeheartedly to make this effort possible. 1. Stripcal is a program developed by Dave Quint, Hewlett-Pack ard Colorado Integrated Circuits Division. It uses transmission line analytical equations to calculate R, L, and C values. 2. Ind3 is a program developed by Ken Lee, Hewlett-Packard Cir cuit Technology Group, It uses the method described in A.E. Ruehli, "Inductance Calculations in a Complex Integrated Circuit Environment," IBM Journal of Research and Development, Sep tember 1972, pp. 470-481. 3. D.W. Quint, G.L. Brown, and R. Kaw, "Measurement of R, L, and C Parameters in VLSI Packages," Proceedings of the 1988 Design Technology Conference, Hewlett-Packard Company, pp. 324-331. Additional information can be found in: 4. D.W. Quint and Asad Aziz, "Electrical Design Methodology of a 407-pin Multilayer Ceramic Package," Proceedings of the 1989 EJectronic Components Conference, Hewlett-Packard Company, pp. 392-398. 5. F. Perezalonso, B. Crawford, R. Kaw, and R. Bernard, "Investi gation of R, L, and C Measurement Techniques for VLSI Packages," Hewlett-Packard Company, September 1988. Published as "Elec trical Characteristics of VLSI Packages," Proceedings of the 1989 Design Technology Conference, Hewlett-Packard Company, pp. 110-119.

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Statistical Circuit Simulation of a Wideband Amplifier: A Case Study in Design for Manufacturability Statistical variations of integrated circuit parameters are often correlated, not independent. Examples are side-byside resistor values and matched transistor gains. Accounting for these correlations using principal component analysis can make statistical simulation an accurate predictor of manufacturing data. by Chee K. Chow IN INTEGRATED CIRCUIT DESIGN, there is a need for statistical circuit simulation that can accurately project circuit performance distributions in manufacturing. There are two reasons for this need. First, being able to project the performance distributions precisely in the de sign phase enhances the chance of a first-pass success. Thus, the cycle time from the design phase to manufactur ing release can be significantly reduced. Second, simula tion can serve as a diagnostic tool to identify hidden process problems. For example, large discrepancies between the simulated and manufactured distributions frequently indi cate process anomalies not previously discovered. A simple approach to statistical circuit simulation is to perform a large number of Monte Carlo simulations.1 The inputs to these simulations are computer-generated ran dom circuit parameters based on the means and standard deviations of the circuit elements extracted from the man ufacturing data. A significant drawback of this approach is that it does not account for the highly correlated nature of the device parameters within an integrated circuit die and also among dice. Consequently, it rarely gives accurate predictions. In integrated circuits, device parameter variations are separable into two types. Variations across many dice, waf ers, or fabrication lots are random in nature, while those within a die are highly correlated. Examples of the latter type are the side-by-side layouts of resistors and matched transistor pairs. At present, commercially available circuit simulators do not address these intercorrelations, so they do not provide the information needed. This article describes a circuit simulator study that ac counts for both the intradie device correlations and the lot-to-lot random variations. The technique used is based on principal component analysis, a branch of multivariate statistics. Examples are presented showing the application of this technique to a custom wideband bipolar amplifier 1C used in the HP 54503A digitizing oscilloscope. The tech nique was used to set an accurate specification early in the design stage and to identify a process problem affecting the circuit performance.

Principal Component Analysis

Consider an integrated circuit having n parameters such as resistor values and transistor gains. These parameters vary statistically from lot to lot, from wafer to wafer, and from die to die because of the time and spatial variations of the fabrication process. The manufacturing distributions for this 1C can be simulated if an ensemble of n-variable vectors can be generated having the same statistical vari ation as the circuit parameters. The accuracy of these simu lations depends to a large extent on how accurately the intercorrelations of the n variables are accounted for. The n-variable vectors can be generated by multivariate statistical techniques,2'3 starting from the correlation ma trix of the n variables. Multivariate statistics analyzes the structure of complex statistical variables to identify latent factors (factor analysis) or the principal components (prin cipal component analysis). A comprehensive treatment of this subject can be found in the literature.2'3 Multivariate statistics has been used extensively by behavioral scientists to analyze latent factors responsible for certain behavior traits. Its applications to manufacturing problems, based on our literature survey, have been very limited.4'5'6'7 One method of solving for the ensemble of n-variable vectors is based on principal component analysis tech niques. Briefly, principal component analysis describes the variances of the n random variables in terms of a set of mutually orthogonal or statistically independent (uncorrelated) variables known as principal components. Each prin cipal component accounts for a portion of the total variance larger than the succeeding components. Statistical ensem bles of the n variables can be readily generated from random numbers after the transformation to the principal compo nents because of the statistical independence of the princi pal components. The ensemble of n-variable vectors is generated in a closed-form solution starting from the n-variable correla tion matrix R, provided that the eigenvalues of R are all positive and the variables are normally distributed. For a set of n circuit variables, ya, y2, ..., yn having a correlation matrix R, it can be shown that the ith statistical variable

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High-Frequency Output

y¡ is given by the expression: 2'3 Output Stage

y¡ =

(D Variable Gain Cell •x4

where Xj, x2 xn are normally and independently distrib uted random variables (the principal components). The values for the x¡ in equation 1 are chosen randomly and independently. This is possible because the x¡ are statisti cally independent. The \¡ in equation 1 are the eigenvalues of R. The ¿t¡ and a¡ are the mean and standard deviation of the ith variable. •Yij is the jth component of the ith eigenvector of R. The statistical measures for these variables are obtained from volume manufacturing data.

Control Register

T T

User Input (Circuit Element Correlation Matrix)

Statistical Package— Main Program

Transconductance Stage Gain

Input Voltage

Fig. 2. Simulation was used to set the minimum gain specifi cation for this programmable gain circuit portion of an inte grated amplifier 1C.

Circuit Simulation Algorithm

A circuit simulator6 was written in C and HP-UX scripts. It runs on an HP 9000 Series 370 workstation. The algorithm of this program is shown in Fig. 1. It consists of three modules: • A statistical analysis package performs all the computa tions according to equation 1. • A parser retrieves these correlated vectors and generates the HP Spice text files. • HP Spice performs the simulations. The user is required to input three pieces of information: (1) the HP Spice text file, (2) the correlation matrix of the circuit variables, and (3) the means and standard deviations of the circuit variables. Data for (2) and (3) has been com piled from volume production measurements for many HP fabrication processes. The confidence limits of the simulated distributions vary as the square root of the number of simulations.1 Based on numerous case studies, about 100 simulations are adequate to project a 95% confidence limit, even for a fairly complex system. Although these Monte Carlo simulations are com putationally intensive, with the emergence of widely avail able high-performance workstation-class computers, they can be routinely performed. A typical 200-sample simula-

x4 Gilbert Gain Cell

tion takes 149 seconds on an HP 9000 Model 370 worksta tion. Case Study

The merits of this statistical circuit simulator are illus trated by two applications during the manufacturing re lease of a custom high-speed integrated circuit. The circuit is an integrated amplifier fabricated using the HP5 process, a 5-GHz fT oxide isolation process. The 1C is used in the HP 54503A low-cost, high-performance digitizing oscilloscope. This custom 1C is the heart of an amplifier/attenuator assembly that accurately reproduces signals from dc to 500 MHz and from 40 mV to 40V with ac or dc coupling and a constant output dynamic range of 500 mV. The 1C consists of nine functional blocks. On-chip 35 -r-

30 --

25 -Principal Component Analysis Correlated Vector Generation

20 --

15 -HP Spice Text File Generation

10 --

•^Hi

HP Spice Text Files

HP Spice Simulation

HP Spice Simulator

T Parameter Extraction

1.30 Data Analysis I Statistical Package

Fig. 1. Statistical circuit simulation algorithm.

1.35

1 . 4 0 1 . 4 5 Minimum Amplifier Gain

1.50

1.55

Fig. 3. The distribution of the minimum gain from 220 corre lated simulations has a mean of 1.44 and a standard deviation of 0.04. It predicts a minimum gain specification of 1.33 to 1.57.

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registers can program the gain from 1.5 to 12.5 in 3% incre ments. Projection of Manufacturing Specifications

In the manufacturing release of this 1C, no reliable data was available to set the minimum gain specification (1.5 nominal) of the programmable gain circuitry shown in Fig. 2. This gain cell can be programmed to amplify small sig nals with a nominal gain of 1.5 to 12.5. An inaccurate specification on the minimum gain would cause high parametric yield loss. The statistical simulation techniques described previously were carried out to project the gain distribution in a real-life manufacturing environ ment. For these simulations, 36 circuit elements were iden tified as random variables. The correlation coefficients of these variables were compiled from production data for the HP5 process. Specifically, the following intradie device correlations were accounted for: • Correlations between resistors • Correlations between transistor model parameters • Correlations between resistors and transistor model pa rameters. A 200-sample Monte Carlo simulation was carried out. The simulated minimum gain distribution is shown in Fig. 3. It projects a ±3cr specification of 1.33 to 1.57. Measured production data for six months shows a distribution with a mean of 1.43 and a standard deviation of 0.034 (Fig. 4). The measured data projects a specification of 1.33 to 1.53. The simulated and manufacturing statistics are compared in Table I. Statistical Simulation as a Diagnostic Tool

A second example of the power of this simulation technique illustrates its role as a diagnostic tool. The por tion of the 1C under study is the dc restore circuit, which level shifts the complementary high-frequency outputs to the ground level. A block diagram is shown in Fig. 5. From 600

High-Frequency Noninverting Output

High-Frequency Inverting Output

Level-Shifted Output

Fig. 5. A portion of the integrated amplifier 1C showing the operational amplifier and resistor bridge of the level shifting subcircuit. The op amp in this dc restore circuit had a large low-frequency output offset for which the simulation data did not match the production data, suggesting a process anomaly.

Table I Comparison of Simulated and Measured Minimum Gain Distributions

Mean Standard Deviation Specification

Simulated Measured 1.44 1.43 0.04 0.034 1.33-1.57 1.33-1.53

1400 T

T

1200 --

500

1000 -400 -800 -300 -600 -200 -400 -100 --

200 --

1.30

1.35

1 . 4 0 1 . 4 5 1 . 5 0 Minimum Amplifier Gain

1.55

1.60

Fig. 4. Six-month production data has a distribution with a mean of 1.43 and a standard deviation of 0.034. The minimum gain specification is 1 .33 to 1.53.

-100

-80

- 6 0 - 4 0 Output Offset (mV)

-20

Fig. 6. Distribution of the output offset of the op amp from production data. The mean is -49 mV and the standard de viation is 11 mV.

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production data, the low-frequency output offset voltage of the op amp had been observed to be large. The op amp output offset voltage is defined as the output voltage of the op amp when the two high-frequency outputs (inverting and noninverting) are equal. Under balanced conditions, the output offset should be close to zero. It was not known what the standard deviation caused by process latitudes should be. Fig. 6 shows a typical distribution of this param eter from six months of production data. It has a mean of -49 mV and a standard deviation of 11 mV. The op amp circuitry has 22 random variables, of which 12 are highly matched resistors and 10 are the transistor model parameters. Correlated simulations were carried out as for the first example. A 200-sample simulation revealed the distribution of the offset voltage to have a mean of 11 mV and a standard deviation of 3.4 mV. Such a large dis crepancy between the manufactured and simulated distri butions suggests some hidden process anomaly that has not been discovered. Subsequently, the process defect that caused this wide distribution of the output was identified. The circuit was redesigned to desensitize it to the process defect. The dis tribution from one wafer after redesign is compared to the simulated distribution in Fig. 7. The redesigned circuit shows a mean of 6 mV and a standard deviation of 4.8 mV. The simulated values are close to the initial production data. The slight discrepancies of the standard deviations can be accounted for by a variety of second-order effects that were not included in these simulations, most notably variations in metal resistivity and metal-to-metal contact resistance.

20 --

15 -10-5 --

Conclusions

This statistical circuit simulation study has demonstrated the accuracy of this technique in projecting circuit perfor mance distributions in manufacturing. The technique also has a valuable role as a diagnostic tool for troubleshooting process problems. Despite some assumptions used both in the underlying principal component analysis theory and the device modeling, these simulations are accurate enough to be a practical CAD tool in product development. It is hoped that this approach to design for manufacturability, through synergism of volume production data with design simulation tooling as exemplified by this simulation study, will be a significant contribution to manufacturing technology. Acknowledgments

The author would like to acknowledge Tom Resman, the designer of the integrated amplifier, for his assistance in this study and in the manuscript preparation. References 1. J.M. Hammersley and D.C. Handscomb, Monte CarJo Methods, Fletcher & Son, Ltd., 1964. 2. D.F. Morrison, Multivariate Statistical Methods, McGraw-Hill, 1976. 3. R.J. Harris, A Primer o/MuJtivariate Statistics, Academic Press, 1985. 4. S. Inohira, T. Shinmi, M. Nagata, T. Toyabe, and K. lida, "A Statistical Model including Parametric Matching for Analog Inte grated Circuit Simulation," IEEE Transactions on Electron De vices, Vol. ED-32, 1985, p. 2177. 5. O.P, Van Driel, "Factor Analysis as an Initial Tool to Obtain Models for Circuit Analysis," IEE CoJJoquium on Model Parame ters for Circuit Analysis, 1981. 6. C.K. Chow, "Projection of Circuit Performance Distributions by Multivariate Statistics," IEEE Transactions on Semiconductor Manufacturing, Vol. 2, no.2, May 1989, pp. 60-65. 7. A. Study W.R. Dutton, and W.J. McCalla, "Experimental Study of Gummel-Poon Model Parameter Correlations for Bipolar Junc tion Transistors," IEEE Transactions on Solid-State Circuits, Vol. SC-12, 1977, p. 552.

0 --

-10 (a)

10 Output Offset (mV)

20

30

10 Output Offset (mV)

20

30

200 -150 -100 -50 --

-10 (b)

Fig. the (a) The distribution of the output offset voltage of the op amp from 200 correlated simulations has a mean of 11 mV and a standard deviation of 3.4 mV, very different from the production data shown in Fig. 6. (b) The distribution from one production wafer after redesign has a mean of 6 mV and a standard deviation of 4.8 mV, more closely matching the simulation data.

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System Level Air Flow Analysis for a Computer System Processing Unit Numerical simulation of particle traces using finite element modeling and supercomputers gives a good qualitative picture of air f low features. Computed velocity profiles and p r e s s u r e d r o ps hav e reas onably good a ccu ra cy. by Vivek Mansingh and Kent P. Misegades STEADY, VISCOUS, THREE-DIMENSIONAL AIR FLOW within a computer system processing unit has been analyzed using finite element modeling. The objective of the study was to investigate the effective ness of finite element modeling in predicting the air flow characteristics within a computer. A full-scale three-dimen sional finite element model of an HP 9000 Model 850 com puter was created using FIDAP, the finite element code from Fluid Dynamics International. This model consisted of over 60,000 nodes and over 40,000 8-node brick ele ments. Extensive computations were carried out using CRAY Y-MP supercomputers. General flow characteristics,

including velocity profiles and pressure drop across the system, were computed. Numerically calculated particle traces were recorded using video equipment. It was found that numerical simulation of particle traces can show good qualitative features of the flow through the system and the modeling results of velocity profiles through the boards and the system pressure drop have reasonably good accu racy. Project Objective

For the thermal management of air-cooled computers, the key air flow parameters to be determined are the air

I/O Side

O

Fan Location

71 cm

CPU Side

Top View

- 65 cm -

92 cm

Side View

Fig. 1 . HP 9000 Model 850 computer system processing unit (right side of computer in photo). There are six fans.

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Front View

velocities in the computer cabinet and the pressure drop across the system. The air velocity flow characteristics in the system help in designing the system layout at the board and component level while the system pressure drop forms the basis for selecting air movers. Thermal management at the component level also requires the knowledge of board and component level air flow characteristics. Traditionally, pressure drop and flow characteristics within a computer cabinet have been experimentally mea sured on prototypes of the machines. Unfortunately, an accurate prototype can only be available when all the com ponents of a system have been designed. This typically happens only towards the end of a design effort. Therefore, the flow characteristics and the system pressure drop can be accurately measured only after almost all the compo nents of the system have already been designed. If for some reason the pressure drop is found to be excessive or the air flow characteristics are found to be different than ex pected, major design changes may have to be made at the end of the design cycle, resulting in serious product mod ifications and delays. Furthermore, experimental measure ments in a prototype are both difficult and expensive in terms of human effort. It would be advantageous to have modeling tools that can predict these air flow characteristics early in the design process. A model could also easily simulate effects of high altitude, zero gravity, and other conditions. The objective of this study was to investigate the effectiveness of finite element modeling in predicting the air flow and pressure drop characteristics within a computer. Model Development

As mentioned earlier, a full-scale model of an air-cooled

HP 9000 Model 850 computer system processing unit (SPU) was created. A photograph and a drawing of a Model 850 SPU are shown in Fig. 1. A Model 850 SPU is approximately 1 m high, 0.7 m wide, and 0.7 m deep. It has four processor boards and several other memory and I/O boards. The back plane essentially divides the cabinet into two halves: the CPU (central processing unit) side and the I/O side. It has six tube axial fans for cooling, which operate in the suction mode. Four of these fans are for the CPU side and two are for the I/O side. The air inlet is at the top and the outlet is at the bottom. Detailed mechanical drawings showing loca tions and dimensions of the structural components, printed circuit boards, suction fans, flow inlets, and flow outlets were used to create the full-scale model of the system using FIDAP's preprocessor FIPREP and mesh generator FIMESH. The full model was divided into smaller finite elements using 8-node brick elements. Fig. 2 gives a view of the final mesh, consisting of 60,507 nodes and 48,600 elements. From the outset, it was recognized that detailed threedimensional modeling from the system level to the compo nent level, that is, from the overall dimensions of the cabinet down to the smallest component on a board, was impossible, both from a modeling standpoint and because of computation time requirements. For instance, we esti mated that simulating the flow through just one of the CPU boards having a number of RAM chips, PGAs, CPU chips and multifinned heat sinks would require a mesh of ap proximately 60,000 to 100,000 elements and a run time of more than 10 CPU hours. Therefore, it was not possible to model every single component in the system. Since the main focus for this project was on system level characteris tics, a component level simplification in the geometry was made. To model the components on the boards, it was

Fig. 2. A view of the finite element mesh for simulation of the air flow in an HP 9000 Model 850 SPU. The complete mesh consists of 60,507 nodes and 48,600 8-node brick elements.

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COMPUTER AIRFLOW AT ASSEMBLY LEVEL - CRAY SIMULATION

VELOCITY VECTOR PLOT SCALE FACTOR 0.1000E+03 MAX. VECTOR

PLOTTED 0.5064E+01 AT NODE 61127

PLANE COEFF.S A O.OOOE+00 B 0.100E+01 C O.OOOE+00 D -.450E+00 VIEW DIRECTION VX -.100E+01 VY 0.300E+00 VZ 0.800E+00 ANG -. lOOE+03 FIDAP 4.51 lO-Nov-89 17: 48: 02

assumed that between any two printed circuit boards, a certain percentage of the flow passage was blocked by com ponents. Based on good engineering judgment, for the four CPU printed circuit boards the blockage was assumed to represent 30% of the volume between two adjacent boards, whereas for all the other boards the blockage was assumed to represent 50% of the volume between adjacent boards. Flow deflection vanes at the air inlet of the cabinet were

Fig. 3. Computed flow velocities in the X-Z plane at the entrance to the printed circuit boards.

included in the model as infinitely thin plates at the same angle as the actual vanes. Although the computational effort required to generate this three-dimensional model was moderate, it took ap proximately IVz engineer-months to create the model be ginning from mechanical drawings. It is also important to note that the use of computer graphics was essential to the successful creation of this mesh, visual analysis of the mesh

COMPUTER AIRFLOW AT ASSEMBLY LEVEL - CRAY SIMULATION

VELOCITY VECTOR PLOT SCALE FACTOR 0.1000E+03 MAX. VECTOR

PLOTTED 0.2831E+01 AT NODE 61143

PLANE COEFF.S A 0.100E+01 B O.OOOE+00 C O.OOOE+00 D -.400E+00 VIEW DIRECTION VX -.100E+01 VY 0.300E+00 VZ 0.800E+00 ANG -.100E+03

FIDAP 4.51 lO-Nov-89 17: 40: 56

84 HEWLETT-PACKARD JOURNAL OCTOBER •

© Copr. 1949-1998 Hewlett-Packard Co.

Fig. 4. Computed flow velocities in the Y-Z plane through the printed circuit boards.

COMPUTER AIRFLOW AT ASSEMBLY LEVEL - CRAY SIMULATION

VELOCITY VECTOR PLOT SCALE FACTOR 0.1000E+03 MAX. VECTOR PLOTTED 0.866aE+01 AT NODE 60548

E+01

¡ Ã-8i l+oo

CORNER SURFACE CUT

VIEW DIRECTION VX -.100E+01 VY 0.300E+00 VZ 0.800E+00 ANG -.100E+03

FIDAP 4.51 lO-Nov-89 17: 37: 07

generator's results being the only good means of checking progress. For this, both FIDAP's postprocessor FDPOST and Cray's Multi-Purpose Graphics System MPGS were used. All computations, including graphics, were per formed on CRAY Y-MP supercomputer systems.

Fig. 5. Computed flow velocities through the system.

Boundary Conditions

The physical problem modeled was three-dimensional, steady, viscous, laminar, isothermal flow. Because the ve locity through the system was of the order of 2 m/s and the length scales of the components were small, the flow was assumed to be laminar. The flow was assumed to be isothermal because the main focus of the problem was the

Fig. 6. Animation of simulated particle traces representing the air flow.

OCTOBER 1990 HEWLETT-PACKARD JOURNAL 85

© Copr. 1949-1998 Hewlett-Packard Co.

fluid flow characteristics. On all solid surfaces of both physical and blocked re gions, a no-slip velocity boundary condition was specified. At the two air flow entrances on the top front and back of the cabinet, no boundary conditions were set. For the air outlet at the bottom of the cabinet, a constant-velocity bound ary condition was defined. However, for the outlet bound ary condition, not enough information was available ini tially. The flow rate produced by a fan is dependent on the pressure drop it experiences. Flow rates are given in tabular or graphical form as a function of pressure drop. The data used in this work was for the fans running at 60 Hz at sea level. Since we did not know the pressure drop of the system at the outset, it was not possible to know the fan flow rate that would define the air exit boundary con dition. To get around this problem, the following iterative procedure was used: 1. An initial fan flow rate was guessed. 2. For this given fan flow rate, the flow field including the pressure drop was calculated based on the uniform exit velocity across the exit area that would result in the same volumetric flow rate as produced by six fans. 3. For this computed pressure drop, the corresponding flow rate from the fan manufacturer's performance curve was found. 4. An average of this new flow rate and the previously guessed flow rate was used to calculate the exit velocities, which were used as new boundary conditions for the next computation. 5. This procedure was repeated until the guessed flow rate produced the corresponding pressure drop according to the fan curves. Computations

The three-dimensional Navier-Stokes equations of mo tion1 were solved in the nondimensional form. The solution technique used was the segregated method.2 A separate linear system was solved for each of the four degrees of freedom — three velocity components and pressure. Relaxa tion factors2 used for the four degrees of freedom were 0.8, 0.8, 0.8 for the three velocity components and 0.0 for pres sure. To improve the accuracy and stability of the solution, an up winding factor2 of 1.0 was used for all degrees of freedom for all computations because high velocity gra dients were expected in the coarse mesh regions. Starting from an initial linear Stokes flow solution, the problem was run for five iterations using the segregated solver, resulting in the following solution or convergence errors for the four degrees of freedom: • X Velocity: 0.0084 • Y Velocity: 0.0074 • Z Velocity: 0.0038 » Pressure: 0.021. The FÃDAP User's Manual recommends that these values be driven to 0.001 when using the segregated solver. How ever, we were not able to converge to values lower than these even though several other values of relaxation and upwinding parameters were tried. After the initial five-iteration solution, a new fan flow rate was guessed and a second run was made. The solution was said to have converged when the pressure error was

less than or equal to that of the first run, 0.021. The results of this iterative procedure are given below: Typical FIDAP Run Run Number of Fancfm Pressure Pressure Drop Fancfm Iterations Guessed Error Computed Actual 1 5 1 0 0 0 . 0 2 1 0 . 4 6 i n H 2 O 2 7 8 5 0 . 0 1 6 0 . 4 0 i n H 2 O

7 0 9 0

In this typical example, 12 iterations were required to find a value of fan flow rate within 10% of that actually supplied by the fan. Given that other simplifications in the model had been made, it was felt that this level of con vergence and accuracy was adequate. On the CRAY Y-MP supercomputer, 10 hours of CPU time were required to perform the 12 solution iterations needed. Memory needed was 4.0M words of main memory and 87M words of secondary memory or scratch memory. For scratch memory, a CRAY SSD (solid-state storage de vice) was used. This reduced an otherwise substantial I/O wait time penalty for disc memory devices to a small frac tion of the total run time. Numerical Results

As mentioned earlier, general flow characteristics in cluding the velocity profile and the pressure drop across the system were computed. Some typical pictures of the flow velocities through the system are shown in Figs. 3, 4, and 5. These illustrate well the qualitative features of the flow entering the CPU side and the I/O side at the top section, turning and going through the printed circuit boards, and exiting the fan outlet region. An interesting aspect of the results is that a substantial portion of the flow entering the I/O side or the rear of the cabinet actually passes over the backplane obstruction in the top section and flows to the CPU side at the front of the cabinet. It can also be seen that" the velocities are low at the entrance, increase between board slots and then decrease again at the exit of the board slots. The air velocities are higher in the four CPU board slots than in the memory and I/O board slots and are in the range of about 1 to 2.75 m/s. As mentioned earlier, simulated particle paths or traces were recorded on video. The traces represent the path that a massless particle would take through the computer cab inet if released at various locations along the inlet planes. Such traces are very useful in giving a qualitative represen tation of the three-dimensional complex flow field. Using MFCS, the Multi-Purpose Graphics System from Cray Re search, these traces were animated to show the details of the flow. The animation very clearly shows the cross flow of air from the I/O side of the cabinet to the CPU side and other complex features of the flow. A typical picture of particle simulation is shown in Fig. 6. Experimental Results

Experimental measurements of the air velocities were carried out on an actual system with the help of a hot-wire anemometer. The cabinet walls and some of the boards were modified so that the hot wire could be inserted into the cabinet at the desired locations. Velocity profiles were

86 HEWLETT-PACKARD JOURNAL OCTOBER 1990

© Copr. 1949-1998 Hewlett-Packard Co.

Conclusions

3.0 -r

1.0 2 0 2 5 Slot Depth (cm) Experimental Computational Results Results

Fig. 7. Computed and experimental air velocities in CPU board slot 0 at the middle of the board.

measured in the CPU and I/O board region across the boards. A typical velocity profile measured in CPU board slot 0 at the middle of the board is shown in Fig. 7. The slot depth (X in Fig. 3), is plotted on the x axis while the respective velocities are shown on the y axis. It can be seen that the air velocities are in the range of 1.25 m/s to 2.25 m/s. The velocities are about 1.5 m/s at both ends of the board, with the highest velocities of about 2.25 m/s in the middle of the board. One of the reasons for the nonuniformity in the velocity profile is the presence of various com ponents (chips, heat sinks, etc.) on the board. A comparison of the numerical results with the experi mental results is also shown in Fig. 7. The numerical results predict higher velocities in the center and lower velocities near the ends than were actually measured. However, the range of velocities is about 1.5 m/s to 2.75 m/s, which is relatively close to that measured experimentally. It should be noted that in the numerical simulations, the board com ponents were modeled as blockage to the flow, whereas in the experiments, the boards had actual components on them.

Steady, viscous, three-dimensional air flow within a computer SPU has been analyzed using finite element model ing. General flow characteristics including velocity profiles and pressure drop across the system were computed. Nu merically simulated particle traces were recorded using video equipment. It was found that numerical simulation of particle traces can show good qualitative features of the flow through the system. The particle traces show some extremely interesting flow characteristics that could not have been known easily otherwise. The computed velocity profiles through the boards and the computed system pres sure drop have reasonably good accuracy. Modeling pre dicted the air velocities through the CPU board slots to be about 1.5 m/s to 2.75 m/s whereas the experimental mea surements showed about 1.25 m/s to 2.25 m/s. However, finite element modeling can be relatively expensive in terms of computation time. References 1. H. Schlichting, Boundary Layer Theory, McGraw-Hill, 1979. 2. FÃDAP Theoretical Manual, Fluid Dynamics International.

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