Strategies For The Modelling And Simulation Of Asynchronous Computer Architectures

Synchronous VLSI design is approaching a critical point, with clock distribution becoming an increasingly costly and complicated issue and power consumption rapidly emerging as a major concern. Asynchronous digital design styles promise to liberate VLSI systems from clock skew problems, o er the potential for low power and high performance and encourage a modular design philosophy which makes incremental technological migration a much easier task. The desire to exploit the potential advantages o ered by asynchronous logic has recently fueled a revival of interest in asynchronous systems. Modelling and simulation, being at the heart of digital system design, may perform a catalytic role in the quest for the realization of the potentials o ered by asynchronous logic. Hence, the recurrence of interest in asynchronous design has been accompanied by an intense research activity aiming at developing techniques appropriate for modelling and simulating asynchronous systems. Contributing to this e ort, and motivated by the increasing debate regarding the potential use of CSP for this purpose, this thesis investigates the suitability of occam, a CSP-based programming language, for the modelling and simulation of complex asynchronous designs. A modelling approach is introduced which aims to exploit the strong relationship between the semantics of occam and the structure and operation of asynchronous systems, as well as the parallelism inherent in asynchronous hardware to achieve the rapid development of asynchronous architectural simulation models, 15 which may be executed on transputer networks to achieve high performance. The applicability and robustness of the approach is demonstrated by employing it to construct occarm, an occam model of the AMULET1 asynchronous microprocessor. The distributed nature of the proposed modelling approach introduces the problem of maintaining temporal precision and ensure that the causality principle is not violated. The thesis provides a quantitative analysis regarding the timing error introduced in the model if violations of the causality principle are permitted. It then introduces the Program Driven Synchronization Protocol, a novel conservative, deadlock avoidance synchronization technique for dealing with causality problems within the framework of the proposed modelling approach. Monitoring, debugging, termination and load balancing issues are also discussed. 16 DECLARATION No portion of the work referred to in this thesis has been submitted in support of an application for another degree or quali cation of this or any other university or other institution of learning. All trademarks cited within this work are acknowledged by the author. 17 COPYRIGHT AND OWNERSHIP OF INTELLECTUAL PROPERTY RIGHTS 1. Copyright in text of this thesis rests with the Author. Copies (by any process) either in full, or of extracts, may be made only in accordance with instructions given by the Author and lodged in the John Rynalds University Library of Manchester. Details may be obtained from the Librarian. This page must form part of any such copies made. Further copies (by any process) of copies made in accordance with such instructions may not be made without the permission (in writing) of the Author. 2. The ownership of any intellectual property rights which may be described in this thesis is vested in the University of Manchester, subject to any prior agreement to the contrary, and may not be made available for use by third parties without the written permission of the University, which will prescribe the terms and conditions of any such arrangement. Further information on the conditions under which disclosures and exploitation may take place is available from the Head of Department of Computer Science. 18 Preface The author obtained a Diploma degree in Computer Engineering and Informatics from the University of Patras, Greece, in July 1989. He was subsequently awarded a scholarship for graduate studies in Computer Science by the University of Manchester, U.K. In October 1990, he joined the Department of Computer Science at the University of Manchester as a research student (ParSiFal group) and a year later he completed his MSc (Method II-by research). In October 1991 he joined the AMULET group at the Department of Computer Science, University of Manchester to pursue a Ph.D. 19 o & o " & o , K! o X% o , o o # !  o & " K E , o % o o " ! " o % o |||||||||{ To my parents, Konstantinos and Chrysoula, for everything they sacri ced in their life for me And to Evi, for the love and support she gave me all these years 20 \H I# ' " ! " ' ! % o " . X! % &  " # "& o % o o. `A " " " " ! " . K ' ' ! %" &, I# " " " ". `E o' o& o " "&, " o " % , # o "& I# "& o . " K. K ' & |||||||||{ \Ithaca gave you the lovely journey. Without her you would never have set out. But she has nothing more to give you. And if you nd her poor, Ithaca has not deceived you. Wise as you will have become, so full of experience, you must have understood already the meaning of Ithacas. " C. Cavafy. 21 Acknowledgements I am grateful to my supervisor, Dr. J. V. Woods, for everything he did for me during the four years in which the research for this thesis was carried out. Professor S. B. Furber, as the director of the AMULET group, has always been a source of inspiration; for this, for his advice and guidance during the initial stages of this research, and for patiently providing me with the facilities to carry out the research for this thesis I express my thanks. I also wish to thank Dr. P. Capon, for allowing me access to the T-Rack, and for his invaluable assistance during the implementation of the occam systems required for the research presented in this thesis. Thanks are also due to all those who supported the T-Rack the last four years, allowing me to complete my research. I would also like to thank all the members of the AMULET group for their support all these years. In particular, I wish to express my thanks to Rob Kelly, (now with ICL, Manchester), Paul Day, Nigel Paver and Steve Temple for always being prepared to discuss and provide answers to my questions regarding the peculiarities of the AMULET1 architecture; Rob's help during some crucial moments of the work was invaluable. David Jackson, Craig Farnsworth, Rahul Mehra, Rhod Davies, Jim Garside, Oleg Petlin, Steve Nicklin, Dave Gilbert, they all helped me in a number of occasions and I thank them all. Nigel also provided his Lapwing Court `mansion', which proved an excellent environment for writing up this thesis, not least because of his strict \Ph.D policing"; my special thanks. The research presented in this thesis was funded by the University of Manchester and by the Mpakalas Foundation, Athens, Greece; I gratefully acknowledge this support. The many friends I made during my ve year stay in Manchester have been an invaluable source of emotional support and have made the Ph.D a less stressful task to undertake and Manchester a great place to live; I thank them all. Eudokia and Vaso, with their parties and joyful lifestyles helped to release some of the frustration of the Ph.D work and made the time I spent with them at 42 Egerton Road, Fallow eld, unforgettable; for that and for taking good care of me, I wholeheartedly thank them. George Tsakogiannis has been a continuous source of support and encouragement ever since we met in Manchester, back in 1990; his support during some very crucial moments of the work for this thesis was catalytic for its continuation and completion. Wael Fahmi's presence in Manchester had 22 always been a source of optimism and positiveness, a window of light in the dark surroundings; my feelings for him could not be possibly expressed in words. I also wish to express my special thanks to Fenia, Aris, Eirini, Xrysa and So a, for their genuine interest in my wellbeing while abroad, and for making me feel at home every time I visited Greece. My parents, Kostantinos and Chrysoula, and my sister Eleni, have been a constant source of moral and nancial support, throughout my life. I could not possibly give back to my parents what they have lost in their e ort to support me I try to honour their sacri ce. I have dedicated this thesis to them with love, respect and gratitude. Last but not least, my deepest love and gratitude to Evi, who has stood by me like nobody else all these di cult years, and has o ered me her support, encouragement, love and life despite the separation. I dedicate this thesis to her too, with all my heart.