Our growing dependence on increasingly complex computer and software systems necessitates the development of formalisms, techniques, and tools for assessing functional properties of these systems. One such technique that has emerged in the last twenty years is model checking, which systematically (and automatically) checks whether a model of a given system satisfies a desired property such as deadlock freedom, invariants, and request-response properties. This automated technique for verification and debugging has developed into a mature and widely used approach with many applications. Principles of Model Checking offers a comprehensive introduction to model checking that is not only a text suitable for classroom use but also a valuable reference for researchers and practitioners in the field. The book begins with the basic principles for modeling concurrent and communicating systems, introduces different classes of properties (including safety and liveness), presents the notion of fairness, and provides automata-based algorithms for these properties. It introduces the temporal logics LTL and CTL, compares them, and covers algorithms for verifying these logics, discussing real-time systems as well as systems subject to random phenomena. Separate chapters treat such efficiency-improving techniques as abstraction and symbolic manipulation. The book includes an extensive set of examples (most of which run through several chapters) and a complete set of basic results accompanied by detailed proofs. Each chapter concludes with a summary, bibliographic notes, and an extensive list of exercises of both practical and theoretical nature.

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Principles of Model Checking

A new class of models, formalisms and mechanisms has recently evolved for describing concurrent and distributed computations based on the concept of ``coordination''''. The purpose of a coordination model and associated language is to provide a means of integrating a number of possibly heterogeneous components together, by interfacing with each component in such a way that the collective set forms a single application that can execute on and take advantage of parallel and distributed systems. In this chapter we initially define and present in sufficient detail the fundamental concepts of what constitutes a coordination model or language. We then go on to classify these models and languages as either ``data-driven'''' or ``control-driven'''' (also called ``process-'''' or ``task-oriented''''). Next, the main existing coordination models and languages are described in sufficient detail to let the reader appreciate their features and put them into perspective with respect to each other. The chapter ends with a discussion comparing the various models and some conclusions.

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Coordination models and languages

Principles of Asynchronous Circuit Design - A Systems Perspective addresses the need for an introductory text on asynchronous circuit design. Part I is an 8-chapter tutorial which addresses the most important issues for the beginner, including how to think about asynchronous systems. Part II is a 4-chapter introduction to Balsa, a freely-available synthesis system for asynchronous circuits which will enable the reader to get hands-on experience of designing high-level asynchronous systems. Part III offers a number of examples of state-of-the-art asynchronous systems to illustrate what can be built using asynchronous techniques. The examples range from a complete commercial smart card chip to complex microprocessors. The objective in writing this book has been to enable industrial designers with a background in conventional (clocked) design to be able to understand asynchronous design sufficiently to assess what it has to offer and whether it might be advantageous in their next design task.

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Principles of Asynchronous Circuit Design: A Systems Perspective

A theory of automatic hierarchical verification of speed-independent circuits is developed and implemented. The theory models circuits as trace structures. Trace structures represent the behaviors of circuits as sets of traces, which sequences of transitions on the circuit's input and output wires. Trace structures form a compositional semantics for circuits: two trace structures can be composed to model connecting the corresponding circuits and transitions can be hidden to model unobservable internal wires. Trace structures express requirements on the behavior of the environment in addition to describing the behavior of a circuit. It is noted that, for composition to work properly, a trace structure must model all possible actions of the environment. This property, called receptiveness, is precisely characterized.
Trace structures can also be used as specifications. If one trace structure can be safely substituted for another in all contexts, the first is an implementation of the second. This relationship can be tested by using a decision procedure based on finding the most demanding environment with which a trace structure can be composed. The use of a single formalism for descriptions and specifications greatly simplifies the theory. More importantly, the resulting verification methodology is naturally hierarchical, because specifications at one level of abstraction can be used as descriptions at higher levels of abstraction.
Two distinct theories are proposed: prefix-closed trace structures, which can model and specify safety properties, and complete trace structures, which can also deal with liveness and fairness properties. The theory of prefix-closed trace structures has been implemented in an interactive program which has verified and detected bugs in published circuit designs.
Complete trace structures are based on regular languages of infinite sequences. The definitions and results pertaining to complete trace structures are very similar to those for prefix-closed trace structures. It is relatively difficult to define and test receptiveness for complete trace structures. The definition of this property is presented in terms of infinite two-player games. The problem of receptiveness is proved to be decidable, by reduction to Church's solvability problem.

Trace Theory for Automatic Hierarchical Verification of Speed-Independent Circuits

We present a new formalism called Gamma in which programs are described in terms of multiset transformations. A distinguishing property of Gamma is the possibility of expressing algorithms in a very abstract way, without any artificial sequentiality. The expressive power of the formalism is illustrated through a series of examples chosen from a wide range of domains (string processing problems, graph problems, geometric problems...).

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Programming by multiset transformation

: We discuss a class of concurrent computations, or special-purpose computing engines, that may be characterized by (i) they consist of regular arrangements of simple cells; (ii) the arrangement consumes streams of input values and produces streams of output values; (iii) the cells communicate with a fixed number of neighbor cells only; (iv) the communication behaviors of the cells are independent of the values communicated. Such arrangements are often referred to as systolic arrays. Our computations, however, have a few other characteristics that are usually not found among systolic arrays: (v) synchronization of cells is by message passing only; (vi) each output value is produced as soon as all input values on which it depends have been consumed. The formalism we use to discuss these computations is trace theory [4], [7], [8]. Section 1 is an introduction to trace theory, in which only those subjects are covered that are needed to understand the subsequent sections. Section 2, called Data Independence, addresses the question what it means that communication behaviors are independent of the values communicated. To express the simplicity of (the communication behaviors of) the cells we define in Section 3 the concept of conservative processes. The results of Sections 2 and 3 are assembled into a number of theorems that are used in Sections 4, 5, and 6. Each of these remaining sections discusses an illustrative example of a systolic computation: polynomial multiplication, cyclic encoding, and palindrome recognition.

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Trace Theory and Systolic Computations

Parle '89: Parallel Architectures and Languages Europe

The relevance of trace theory to the design of VLSI circuits is discussed. We present an introduction to trace theory and to regular trace structures in particular. We show, in a number of examples, how trace theory can be used to reason about and to prove properties of hierarchical components.

Trace theory and the definition of hierarchical components

In this chapter we analyze the potential of asynchronous circuits for low power consumption We set out by reviewing the mechanisms of energy dissipation of digital CMOS ICs in general and clocked circuits in particular For many applications the generation and distribution of the clock signal account for more than half the power dissipation, directly or indirectly Much of this wasted clock power — and often much more — can be saved by applying asynchronous circuit techniques

VLSI Programming of Asynchronous Circuits for Low Power

A program notation without variables is proposed. The state of a computation is recorded as a set of "associons." Each associon is a tuple of names representing a relation between the entities with those names. The state of the computation can be changed by the creation of new associons representing new relations deducible from those already recorded. The building block prescribing such deductions is called the "closure statement." The notation proposed is the result of our search for a basic statement the execution of which may employ more concurrency than is the case for the traditional assignment statement. Some possible extensions to the notation are discussed.

Martin Rem

Papers

Trace Theory and Systolic Computations

Parle '89: Parallel Architectures and Languages Europe

Trace theory and the definition of hierarchical components

VLSI Programming of Asynchronous Circuits for Low Power

Associons: A Program Notation with Tuples Instead of Variables