HRT-HOOD™: A Structured Design Method for Hard Real-Time Ada Systems HRT-HOOD™: A Structured Design Method for Hard Real-Time Ada Systems REAL-TIME Series Editor: SAFETY Hussein Zedan, Department of Mathematics and Computational Sciences, Liverpool John Moores University, Liverpool, U.K. CRITICAL SYSTEMS Vol. 1 Time and Probability in Formal Design of Distributed Systems (H.A. Hansson) Vol. 2 Towards Verified Systems (J. Bowen, ed.) Vol. 3 HRT-HOOD™: A Structured Design Method for Hard Real-Time Ada Systems ( A. Burns and A. Wellings) REAL-TIME HRT-HOOD™: SAFETY A Structured Design CRITICAL SYSTEMS Method for Hard Real-Time Ada Systems Alan Burns Andy Wellings Department of Computer Science The University of York Heslington, York, U.K. MtOOD is a trademark of the HOOD User Group 1995 ELSEVIER AMSTERDAM • LAUSANNE • NEW YORK • OXFORD • SHANNON • TOKYO ELSEVIER SCIENCE B.V. Sara Burgerhartstraat 25 P.O. Box 211, 1000 AE Amsterdam, The Netherlands ISBN: 0 444 82164 3 © 1995 Elsevier Science B.V. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science B.V., Copyright & Permissions Department, P.O. Box 521, 1000 AM Amsterdam, The Netherlands. Special regulations for readers in the U.S.A. - This publication has been registered with the Copyright Clearance Center Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01932. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the U.S.A. All other copyright questions, including photocopying outside of the U.S.A., should be referred to the copyright owner, Elsevier Science B.V., unless otherwise specified. 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Contents Contents V Foreword IX Preface XI Acknowledgements XIII Real-Time Systems Research at York XV Part 1: Hard Real-Time HOOD 1 Chapter 1: Overview of the HRT-HOOD Design Process 3 1.1 Introduction 3 1.2 The Importance of Non-Functional Requirements 5 1.3 The Software Development Life Cycle 6 1.4 Summary 8 Chapter 2: Logical and Physical Architecture Design in HRT-HOOD 11 2.1 Logical Architecture Design 11 2.2 Physical Architecture Design 14 2.3 Summary 18 Chapter 3: HRT-HOOD Objects 19 3.1 Graphical Representation 19 3.2 Passive Objects 21 3.3 Active Objects 21 3.4 Protected Objects 23 3.5 Cyclic Objects 24 3.6 Sporadic Objects 26 VI Contents 3.7 Real-Time Object Attributes 27 3.8 The Use Relationship (Control Flow) 29 3.9 The Include Relationship (Decomposition) 30 3.10 Operation Decomposition 31 3.11 Object Control Structure and Thread Decomposition 38 3.12 Data Flows 38 3.13 Exception Flows 3 8 3.14 Environment Objects 39 3.15 Class Objects 40 3.16 Distributed Systems 42 3.17 Summary 45 Part 2: Mapping HRT-HOOD Designs to Ada 47 Chapter 4: Supporting Hard Real-Time Systems in Ada 83 and Ada 95 49 4.1 The Ada 83 and Ada 95 Real-Time Models 50 4.2 Supporting Ada 95 Abstractions in Ada 83 51 4.3 Extending the Model 59 4.4 Implementation Cost 62 4.5 Summary 64 Chapter 5: Overall Mapping Approach 65 5.1 HOOD 3.1 to Ada 83 Mapping 65 5.2 An Alternative Translation Approach 68 5.3 Mapping HRT-HOOD to Ada 69 Chapter 6: Mapping of Passive and Active Objects 77 6.1 Passive Terminal Objects 77 6.2 Active Terminal Objects 80 6.3 Class and Instance Terminal Objects 91 Chapter 7: Mapping Protected, Cyclic eind Sporadic Objects 93 7.1 Protected Terminal Objects 93 7.2 Cyclic Terminal Objects 100 7.3 Sporadic Terminal Objects 109 Chapter 8: Distributed Systems 129 8.1 Analysable Communication Subsystem 131 8.2 Mapping to Ada 95 136 8.3. Mapping Protected Objects in a Distributed Ada Environment 140 Contents VII Part 3: Case Studies 143 Chapter 9: The Mine Control System 145 9.1 Mine Control System Overview 145 9.2 The Logical Architecture Design 150 9.3 The Physical Architecture Design 156 9.4 The Object Description Skeleton 160 9.5 Translation to Ada 95 201 9.6 Conclusion 224 Chapter 10: The Olympus Attitude and Orbital Control System 225 10.1 Background to the Case Study 225 10.2 The Modelled System: The Olympus AOCS 226 10.3 The Software Architecture Design 228 10.4 The Physical Architecture Design 242 10.5 Problems Encountered 244 10.6 Summary 246 Chapter 11: Conclusions 247 Appendix A: Terminology 249 Appendix B: HRT-HOOD Definition Rules 253 B.l Design Checking, Scoping and HRT-HOOD Rules 253 B.2 General Definitions 255 B.3 Use Relationship 255 B.4 Include Relationships 256 B.5 Operations 256 B.6 Visibility 258 B.7 Consistency 258 Appendix C: Object Description Skeleton (ODS) Syntax Summary 261 C.l General Declarations 261 C.2 Object ODS Structure 262 C.3 The Visible Part of the ODS 263 C.4 The Hidden Part of the ODS 274 C.5 Parameters of Class objects 280 Appendix D: Textual Formalism — the ODS Definition 281 D. 1 PASSIVE Objects 281 D.2 ACTIVE Objects 284 VIII Contents D.3 PROTECTED Objects 287 D.4 CYCLIC Objects 290 D.5 SPORADIC Objects 295 D.6 ENVIRONMENT Objects 299 D.7 CLASS Objects 299 D.8 Instances of CLASS Objects 300 Appendix E: Device Control Objects in HRT-HOOD 301 References 305 Index 311 IX Foreword The increasing use of computers for real-time control on board spacecrafts has bought with it a greater emphasis on the development methodology used for such systems. By their nature spacecraft control computers have to operate unattended for long periods and because of the programmatics of space, systems are subject to a long development cycle. As a result there are two distinct concerns, the first being that the development approach guarantees functional and timing correctness, the second being that problems, particularly those associated with timing, are considered as early as possible in the spacecraft development life cycle. The European Space Agency has, for a number of years, encouraged the development of software using HOOD. It was thus a natural next step to investigate the incorporation of time within the existing HOOD framework. This has proven to be very beneficial, and this book describes the approach developed by the authors for handling Hard Real-Time applications. It describes both the background scheduling theory, provides practical examples of its application to real life problems, and demonstrates how it is used in the various phases of the development of Hard-Real Time systems. Thus I consider that HRT HOOD is a beneficial addition to the armoury of techniques for developing real-time systems, and that this book is a welcome addition to literature in this area which I can recommend for its insight and practical value. Richard Creasey European Space Research and Technology Centre