,DOCUMENT RESUME ED 082 488 BM 011 457 , _ AUTHOR Schultz, Gary D. 1 TITLE The CHAT System:1)ln OS/360 MVT Time-Sharing Subsystem for Displays and Teletype. Technical Progress Report. INSTITUTION North Carolina Univ., Chapel Hill. Dept. of Computer Science. SPONS AGENCY National Science Foundation, Washington, D.C. REPORT NO UNC-TPR-CAI-6 PUB DATE May 73 NOTE 225p.; Thesis submitted to the Department of Computer Science, University of North Carolina EDRS PRICE MF-$0.65 HC-:-$9.87 DESCRIPTORS Computer Programs; Input Output Devices; *Interaction; *Man Machine Systems;, Masters Theses; Program Descriptions; *Systems DeVelopment; Technical Reports; *Time Sharidg IDENTIFIERS *Chapel Hill Alphanumeric Terminal; CHAT; CRT Display Stations;. OS 360; PI. I; Teletype ABSTRACT The design and operation of a time-sharing monitor are described. It runs under OS/360 MVT that supports multiple application program interaction with operators of CRT (cathode ray tube) display stations and of .a teletype. Key. design features discussed include:1) an interface. allowing application programs to be coded in either PL/I or assembler language; 2) use of the teletype for:subsystem control and diagnostic purposes; and 3)a novel interregional conduit allowing an application program running under the Chapel Hill Alphanumeric Terminal (CHAT)_: monitor to interact--like a terminal operator--with a conversational language processor in another region of the OS/360 installation. (Author) FILMED FROM BEST A7AILABLE COPY University of North Carolina atChapel Hill Department of Computer Science CO -4. CNJ CO THE CHAT SYSTEM: AN OS/360 MVT TIME-SHARING SUBSYSTEM FOR DISPLAYS AND TELETYPE LiJ Gary D. Schultz May 1973 Technical Progress Report CAI-6 to the National Science Foundation under Grant GJ-755 U.S. OE PAR THE NT OF NEAL1N. EDUCATION &WELFARE NATIONAL INSTITUTE OF EDUCATION THIS DOCUMENT HAS BEEN REAM). DUCED EXACTLY AS RECEIVED FROM mePERSON OR ORGANIZATION ORIGIN- ATING IT. POINTS OP VIEW DR OPINIONS STATED DO NOT NECESSARILY REPRE- SENT OFPIciAL NATIONAL INSTITUTE OF EDUCATION POSITION OR POLICY. DEPARTMENT OF COMPUTER SCIENCE University of North Carolina at Chapel Hill THE CHAT SYSTEM: AN OS/360 MVT TIME-SHARING SUBSYSTEM FOR DISPLAYS AND TELETYPE by . Gary D. Schultz A thesis submitted to the faculty of the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Master of Science in the Department of Computer Science. Chapel Nil1, 1973 Approved by: A Crte Adviser GARY DENNIS SCHULTZ. The CHAT System: An OS/360 MVT Time-Sharing Subsystem for Displays and Teletype. (Under the direction of DR. FREDERICK P. BROOKS, JR.) This thsis describes the design and operation of a time-sharing monitor running under OS/360 MVT that supports multiple application pro- gram interaction with operators of CRT display stations and of a Teletype. Some key features of the design are (1) an interface allowing applica- tion programs to be coded in either PL/I or assembler, (2) use of the Teletype for subsystem control and diagnostic purposes, (3) a novel interregional conduit allowing an application program running under the CHAT monitor to interact--like a terminal operator--with a conversa- tional language processor in another region of the 05/360 installation. II AC_...NOWLEDGMENTS I extend ic profound appreciation to William H. Blair for his collaboration in making the CHAT System a working reality. Throughout the two-and-a-half years of system development, I benefited daily from his insights and assistance and his unrivaled dedication to quality work. His companion thesis 11331, and the many references to it herein, only reveal his technical contributions to the project. For his other contributions, I thank him heartily. I also thank J. Craig Mudge for his willingness to assist in testing sessions at all hours of day and night--sacrificing his own scarce time to do so. Dr. Frederick P. Brooks, Jr,, gave valuable criticism and advice on early drafts of this thesis, improving its organization, style, and clarity. For this, the readers will perhaps thank him as much as I do. Partial support of the project was funded by the National Science Foundation under NSF Grant Number CJ-755. TABLE OF CONTENTS Acknowledgments ii 1. INTRODUCTION 1 Concerns and Organization of the Thesis 4 Related Literature 10 2. SYSTEM OVERVIEW 16 Hardware Specifics 17 Configuration 17 Operation 19 Terminal Usage 26 Organization and Functions of the Monitor 34 Task Structure and Control 36 Core Layout and Intraregional Protection 38 Communication and Linkage 45 Initialization of the Region 56 3. THE APPLICATION PROGRAM INTERFACE 62 Display Usage 64 Controlling the Slide Projector 64 Writing on the Display Screen 65 Reading from the Display 69 Getting the Lightpenned Coordinates 70 Time and Keyboard Synchronization 72 Teletype Usage 75 CPS Access 76 Establishing Connection to CPS 76 Reading from CPS 76 Writing to CPS 78 Interrupting CPS Activity 78 General Use Procedures 80 Exception-Condition Signalling 82 Writing an Application Program 84 4. REGION AND SUBTASK CONTROL 87 Time-Slicing 89 Subtask Priority Scheduling 96 Remarks,on Scheduling 102 Other Executive.Functions 104 iv 5'. *DISPLAY I/O MANAGEMENT 105 An Initialization Step 107 Waiting, Linking, and Queueing 110 Insensitivity to Number of Displays 115 Scheduling Rule 117 Servicing Attentions 120 IN Initiation and Completion 123 Channel Programming 123 Completion and Posting 124 Hard Error Handling 1 126 Shutdown 127 6. TELETYPE CONSOLE SUPPORT 128 Details on Teletype Usage 130 Modes 130 Paper Tape 131 Ending a Message 131 Monitor Commands 133 Measages Sent to the Teletype Operator 136 Structure.of the Teletype Support 140 7. THE INTERREGIONAL CONDUIT 143 Design of the Conduit: Linkage and Functions 146 Inside the Conduit 153 Initialization and Checking, 153 How CPS Works 161 Simulating the Teletype 165 Experience with the Conduit 176 ,8. ON-LINE TERMINAL TEST FACILITY 177 Objectives and Usage . 181 The I/O Interface for OLTEST 183 Commands 193 OUtput for the LOG Command . 202 9. FACTS AND FIGURES- 208 CHAT Parameters.and How to Change Them 209 Storage Requirements 212 References 215 :Appendix A.List of Acronyms '218 AppendiX.B.. Code Listings (SeparateCover) The way to avoid the machine taking command is not to take more and longer vacations from a life dominated by machines, or from a machine regulatdd existence. The solution lies in finding ways to make this an age where humanity dominates despite the use- fulness of machines, and to do this by making fullest use of their convenience.... ...The advantages of the wachines are so obvious and so desirable, that we tend to become, small step by small step, seduced into ignoring the price we pay for their unthinking use. The emphasis here is on unthinking use, because they all have their good uses. But the'most careful thinking and planning is needed to enjoy the good use of any technical contrivance. without paying a price for it in human freedom. Bruno Bettelheim The Informed Heart CHAPTER 1: WIRODUCTION The Chapel Hill Alphanumeric Terminal (CHAT) System is a complex of computer-linked terminals for which access to a library of inter- active programs is supported by a time-sharing monitor operating under OS/360 BVT. The terminal complex consists of (1) a cluster of display stations sharing, by program-controlled multiplexing, a single link to the computer and (2) a Teletype connected by common-carrier dial-up facilities. The program library includes a number of application programs, created by students and faculty of the University of Borth Carolina Computer Science Department as part of the Department's research project in computer-assisted instruction (CAT). These programs cover a variety of applications, including a gamut of student-, teacher-, and author-controlled CAI as well as some on-line services similar to those present in other time-sharing systems. With respect to the CAI Project emphasis and intended terminal usage, the CHAT System centers around the display stations, each of which is a multicomponent unit--including keyboard and lightpen for data entry and four-color CRT and random-access slide projector for display of out- put. The program library reflects this focus, with most applications of importance and complexity being designed for interaction with the display stations. The Teletype plays an important role in terms of remote operator control of the CHAT programming subsystemsomewhat akin to the computer console control of the overall ine.i1 -rion multipro- 2 gramming system. By means of a primitive command language, the Tele- type operator can communicate directly with the CHAT ?Wnitor for purposes of subsystem control and fault diagnosis. It is also possible to invoke an application program from the Teletype and, indeed, sub- system control can be interleaved with application program interactions if desired. Some of the application programs in the CHAT program library _antedate the existence of the CHAT System, having undergone interface and/or device-adaptive changes prior to inclusion in the system. Brownlee's PAMELA [B4], an interactive assembler for the System/360 assembler language, was originally written for a standalone CC-30 display terminal--the same display, used in the CHAT cluster--but using a display - I/O interface entirely different from that presented by the CHAT Monitor. Pikaplot [B2] was adapted for a standalone CC-30 from Oliver's numerical analysis laboratory simulator [01] for the IBM 2250 graphics-display. Pikaplot exploits the slide projector to capture some of the power of the 2250's graphics facility and originally used a display I/O interface different from both PAMELA's and CHAT's. Hypertext [C1], Brown Uni- versity's text editing system, also for the 2250; was adapted by Wait [Wl] for the CHAT System displays directly. Of the major members of the program library, only Mudge's DIAL [Ml] was developed exclusively with the CHAT System in mind.