Completion Detection In Asynchronous Circuits

This book is intended for designers with experience in traditional (clocked) circuit design, seeking information about asynchronous circuit design, in order to determine if it would be advantageous to adopt asynchronous methodologies in their next design project. The author introduces a generic approach for implementing a deterministic completion detection scheme for asynchronous bundled data circuits that incorporates a data-dependent computational process, taking advantage of the average-case delay. The author validates the architecture using a barrel shifter, as shifting is the basic operation required by all the processors. The generic architecture proposed in this book for a deterministic completion detection scheme for bundled data circuits will facilitate researchers in considering the asynchronous design style for developing digital circuits.

Since the second half of the 1980s asynchronous circuits have been the subject of a great deal of research following a period of relative oblivion. The lack of interest in asynchronous techniques was motivated by the progressive shift towards synchronous design techniques that had much more structure and were much easier to verify and synthesize. System design requirements made it impossible to eliminate totally the use of asynchronous circuits. Given the objective difficulty encountered by designers, the asynchronous components of electronic systems such as interfaces became a serious bottleneck in the design process. The use of new models and some theoretical breakthroughs made it possible to develop asynchronous design techniques that were reliable and effective. This book describes a variety of mathematical models and of algorithms that form the backbone and the body of a new design methodology for asyn chronous design. The book is intended for asynchronous hardware designers, for computer-aided tool experts, and for digital designers interested in ex ploring the possibility of designing asynchronous circuits. It requires a solid mathematical background in discrete event systems and algorithms. While the book has not been written as a textbook, nevertheless it could be used as a reference book in an advanced course in logic synthesis or asynchronous design.

The number of gates on a chip is quickly growing toward and beyond the one billion mark. Keeping all the gates running at the beat of a single or a few rationally related clocks is becoming impossible. In static timing analysis process variations and signal integrity issues stretch the timing margins to the point where they become too conservative and result in significant overdesign. Importance and difficulty of such problems push some developers to once again turn to asynchronous alternatives. However, the electronics industry for the most part is still reluctant to adopt asynchronous design (with a few notable exceptions) due to a common belief that we still lack a commercial-quality Electronic Design Automation tools (similar to the synchronous RTL-to-GDSII flow) for asynchronous circuits. The purpose of this paper is to counteract this view by presenting design flows that can tackle large designs without significant changes with respect to synchronous design flow. We are limiting ourselves to four design flows that we believe to be closest to this goal. We start from the Tangram flow, because it is the most commercially proven and it is one of the oldest from a methodological point of view. The other three flows (Null Convention Logic, de-synchronization, and gate-level pipelining) could be considered together as asynchronous re-implementations of synchronous (RTL- or gate-level) specifications. The main common idea is substituting the global clocks by local synchronizations. Their most important aspect is to open the possibility to implement large legacy synchronous designs in an almost "push button" manner, where all asynchronous machinery is hidden, so that synchronous RTL designers do not need to be re-educated. These three flows offer a trade-off from very low overhead, almost synchronous implementations, to very high performance, extremely robust dual-rail pipelines.

Designing Asynchronous Circuits using NULL Convention Logic (NCL) begins with an introduction to asynchronous (clockless) logic in general, and then focuses on delay-insensitive asynchronous logic design using the NCL paradigm. The book details design of input-complete and observable dual-rail and quad-rail combinational circuits, and then discusses implementation of sequential circuits, which require datapath feedback. Next, throughput optimization techniques are presented, including pipelining, embedding registration, early completion, and NULL cycle reduction. Subsequently, low-power design techniques, such as wavefront steering and Multi-Threshold CMOS (MTCMOS) for NCL, are discussed. The book culminates with a comprehensive design example of an optimized Greatest Common Divisor circuit. Readers should have prior knowledge of basic logic design concepts, such as Boolean algebra and Karnaugh maps. After studying this book, readers should have a good understanding of the differences between asynchronous and synchronous circuits, and should be able to design arbitrary NCL circuits, optimized for area, throughput, and power. Table of Contents: Introduction to Asynchronous Logic / Overview of NULL Convention Logic (NCL) / Combinational NCL Circuit Design / Sequential NCL Circuit Design / NCL Throughput Optimization / Low-Power NCL Design / Comprehensive NCL Design Example

In recent years, there has been a great surge of interest in asynchronous circuits, largely through the development of new asynchronous design methodologies. This book provides a comprehensive theory of asynchronous circuits, including modelling, analysis, simulation, specification, verification, and an introduction to their design.

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.

Asynchronous Circuit Design for VLSI Signal Processing is a collection of research papers on recent advances in the area of specification, design and analysis of asynchronous circuits and systems. This interest in designing digital computing systems without a global clock is prompted by the ever growing difficulty in adopting global synchronization as the only efficient means to system timing. Asynchronous circuits and systems have long held interest for circuit designers and researchers alike because of the inherent challenge involved in designing these circuits, as well as developing design techniques for them. The frontier research in this area can be traced back to Huffman's publications `The Synthesis of Sequential Switching Circuits' in 1954 followed by Unger's book, `Asynchronous Sequential Switching Circuits' in 1969 where a theoretical foundation for handling logic hazards was established. In the last few years a growing number of researchers have joined force in unveiling the mystery of designing correct asynchronous circuits, and better yet, have produced several alternatives in automatic synthesis and verification of such circuits. This collection of research papers represents a balanced view of current research efforts in the design, synthesis and verification of asynchronous systems.

Asynchronous On-Chip Networks and Fault-Tolerant Techniques is the first comprehensive study of fault-tolerance and fault-caused deadlock effects in asynchronous on-chip networks, aiming to overcome these drawbacks and ensure greater reliability of applications. As a promising alternative to the widely used synchronous on-chip networks for multicore processors, asynchronous on-chip networks can be vulnerable to faults even if they can deliver the same performance with much lower energy and area compared with their synchronous counterparts – faults can not only corrupt data transmission but also cause a unique type of deadlock. By adopting a new redundant code along with a dynamic fault detection and recovery scheme, the authors demonstrate that asynchronous on-chip networks can be efficiently hardened to tolerate both transient and permanent faults and overcome fault-caused deadlocks. This book will serve as an essential guide for researchers and students studying interconnection networks, fault-tolerant computing, asynchronous system design, circuit design and on-chip networking, as well as for professionals interested in designing fault-tolerant and high-throughput asynchronous circuits.