Beginning in the mid 1980's, VLSI technology had begun to advance in two directions. Pushing the limit of integration, ULSI (Ultra Large Scale Integration) represents the frontier of the semiconductor processing technology in the campaign to conquer the submicron realm. The application of ULSI, however, is at present largely confined in the area of memory designs, and as such, its impact on traditional, microprocessor-based system design is modest. If advancement in this direction is merely a natural extrapolation from the previous integration generations, then the rise of ASIC (Application-Specific Integrated Circuit) is an unequivocal signal that a directional change in the discipline of system design is in effect. In contrast to ULSI, ASIC employs only well proven technology, and hence is usually at least one generation behind the most advanced processing technology. In spite of this apparent disadvantage, ASIC has become the mainstream of VLSI design and the technology base of numerous entrepreneurial opportunities ranging from PC clones to supercomputers. Unlike ULSI whose complexity can be hidden inside a memory chip or a standard component and thus can be accommodated by traditional system design methods, ASIC requires system designers to master a much larger body of knowledge spanning from processing technology and circuit techniques to architecture principles and algorithm characteristics. Integrating knowledge in these various areas has become the precondition for integrating devices and functions into an ASIC chip in a market-oriented environment. But knowledge is of two kinds.

The VHSIC Hardware Description Language (VHDL) provides a standard machine processable notation for describing hardware. VHDL is the result of a collaborative effort between IBM, Intermetrics, and Texas Instruments; sponsored by the Very High Speed Integrated Cir cuits (VHSIC) program office of the Department of Defense, beginning in 1981. Today it is an IEEE standard (1076-1987), and several simulators and other automated support tools for it are available commercially. By providing a standard notation for describing hardware, especially in the early stages of the hardware design process, VHDL is expected to reduce both the time lag and the cost involved in building new systems and upgrading existing ones. VHDL is the result of an evolutionary approach to language devel opment starting with high level hardware description languages existing in 1981. It has a decidedly programming language flavor, resulting both from the orientation of hardware languages of that time, and from a ma jor requirement that VHDL use Ada constructs wherever appropriate. During the 1980's there has been an increasing current of research into high level specification languages for systems, particularly in the software area, and new methods of utilizing specifications in systems de velopment. This activity is worldwide and includes, for example, object oriented design, various rigorous development methods, mathematical verification, and synthesis from high level specifications. VAL (VHDL Annotation Language) is a simple further step in the evolution of hardware description languages in the direction of applying new methods that have developed since VHDL was designed.

too vast, too complex, too grand ... for description. John Wesley Powell-1870 (discovering the Grand Canyon) VHDL is a big world. A beginner can be easily disappointed by the generality of this language. This generality is explained by the large number of domains covered - from specifications to logical simulation or synthesis. To the very beginner, VHDL appears as a "kit". He is quickly aware that his problem may be solved with VHDL, but does not know how. He does not even know how to start. In this state of mind, all the constraints that can be set to his modeling job, by using a subset of the language or a given design methodology, may be seen as a life preserver. The success of the introduction of VHDL in a company depends on solutions to many questions that should be answered months before the first line of code is written: • Why choose VHDL? • Which VHDL tools should be chosen? • Which modeling methodology should be adopted? • How should the VHDL environment be customized? • What are the tricks? Where are the traps? • What are the differences between VHDL and other competing HDLs? Answers to these questions are organized according to different concerns: buying the tools, organizing the environment, and designing. Decisions taken in each of these areas may have many consequences on the way to the acceptance and efficiently use of VHDL in a company.

A Guide to VHDL, Second Edition is intended for the working engineer who needs to develop, document, simulate, and synthesize a design using the VHDL language. It is for system and chip designers who are working with VHDL CAD tools, and who have some experience programming in Fortran, Pascal, or C and have used a logic simulator. A Guide to VHDL, Second Edition includes a number of paper exercises and computer lab experiments. If a compiler/simulator is available to the reader, then the lab exercises included in the chapters can be run to reinforce the learning experience. For practical purposes, this book keeps simulator-specific text to a minimum, but does use the Synopsys VHDL Simulator command language in a few cases. A Guide to VHDL, Second Edition is designed as a primer and its contents are appropriate for an introductory course in VHDL. The VHDL language was updated in 1992 with some minor improvements. In most cases, the language is upward compatible. Although this book is based primarily on the VHDL 1987 standard, this new second edition indicates the significant changes in the 1992 language to assist the designer in writing upwardly compatible code.

This book constitutes the refereed proceedings of the Second International Conference on Formal Methods in Computer-Aided Design, FMCAD '98, held in Palo Alto, California, USA, in November 1998. The 27 revised full papers presented were carefully reviewed and selected from a total of 55 submissions. Also included are four tools papers and four invited contributions. The papers present the state of the art in formal verification methods for digital circuits and systems, including processors, custom VLSI circuits, microcode, and reactive software. From the methodological point of view, binary decision diagrams, model checking, symbolic reasoning, symbolic simulation, and abstraction methods are covered.

From the Foreword..... Modern digital signal processing applications provide a large challenge to the system designer. Algorithms are becoming increasingly complex, and yet they must be realized with tight performance constraints. Nevertheless, these DSP algorithms are often built from many constituent canonical subtasks (e.g., IIR and FIR filters, FFTs) that can be reused in other subtasks. Design is then a problem of composing these core entities into a cohesive whole to provide both the intended functionality and the required performance. In order to organize the design process, there have been two major approaches. The top-down approach starts with an abstract, concise, functional description which can be quickly generated. On the other hand, the bottom-up approach starts from a detailed low-level design where performance can be directly assessed, but where the requisite design and interface detail take a long time to generate. In this book, the authors show a way to effectively resolve this tension by retaining the high-level conciseness of VHDL while parameterizing it to get good fit to specific applications through reuse of core library components. Since they build on a pre-designed set of core elements, accurate area, speed and power estimates can be percolated to high- level design routines which explore the design space. Results are impressive, and the cost model provided will prove to be very useful. Overall, the authors have provided an up-to-date approach, doing a good job at getting performance out of high-level design. The methodology provided makes good use of extant design tools, and is realistic in terms of the industrial design process. The approach is interesting in its own right, but is also of direct utility, and it will give the existing DSP CAD tools a highly competitive alternative. The techniques described have been developed within ARPAs RASSP (Rapid Prototyping of Application Specific Signal Processors) project, and should be of great interest there, as well as to many industrial designers. Professor Jonathan Allen, Massachusetts Institute of Technology

CHARM '97 is the ninth in a series of working conferences devoted to the development and use of formal techniques in digital hardware design and verification. This series is held in collaboration with IFIP WG 10.5. Previous meetings were held in Europe every other year.

Synchronization is one of the important issues in digital system design. While other approaches have always been intriguing, up until now synchro nous operation using a common clock has been the dominant design philo sophy. However, we have reached the point, with advances in technology, where other options should be given serious consideration. This is because the clock periods are getting much smaller in relation to the interconnect propagation delays, even within a single chip and certainly at the board and backplane level. To a large extent, this problem can be overcome with care ful clock distribution in synchronous design, and tools for computer-aided design of clock distribution. However, this places global constraints on the design, making it necessary, for example, to redesign the clock distribution each time any part of the system is changed. In this book, some alternative approaches to synchronization in digital sys tem design are described and developed. We owe these techniques to a long history of effort in both digital system design and in digital communica tions, the latter field being relevant because large propagation delays have always been a dominant consideration in design. While synchronous design is discussed and contrasted to the other techniques in Chapter 6, the dom inant theme of this book is alternative approaches.

The second half of this century will remain as the era of proliferation of electronic computers. They did exist before, but they were mechanical. During next century they may perform other mutations to become optical or molecular or even biological. Actually, all these aspects are only fancy dresses put on mathematical machines. This was always recognized to be true in the domain of software, where "machine" or "high level" languages are more or less rigourous, but immaterial, variations of the universaly accepted mathematical language aimed at specifying elementary operations, functions, algorithms and processes. But even a mathematical machine needs a physical support, and this is what hardware is all about. The invention of hardware description languages (HDL's) in the early 60's, was an attempt to stay longer at an abstract level in the design process and to push the stage of physical implementation up to the moment when no more technology independant decisions can be taken. It was also an answer to the continuous, exponential growth of complexity of systems to be designed. This problem is common to hardware and software and may explain why the syntax of hardware description languages has followed, with a reasonable delay of ten years, the evolution of the programming languages: at the end of the 60's they were" Algol like" , a decade later "Pascal like" and now they are "C or ADA-like". They have also integrated the new concepts of advanced software specification languages.