The impact of asynchrony on computer architecture

Abstract

The performance characteristics of asynchronous circuits are quite different from those of their synchronous counterparts. As a result, the best asynchronous design of a particular system does not necessarily correspond to the best synchronous design, even at the algorithmic level. The goal of this thesis is to examine certain aspects of computer architecture and design in the context of an asynchronous VLSI implementation. We present necessary and sufficient conditions under which the degree of pipelining of a component can be modified without affecting the correctness of an asynchronous computation. As an instance of the improvements possible using an asynchronous architecture, we present circuits to solve the prefix problem with average-case behavior better than that possible by any synchronous solution in the case when the prefix operator has a right zero. We show that our circuit implementations are area-optimal given their performance characteristics, and have the best possible average-case latency. At the level of processor design, we present a mechanism for the implementation of precise exceptions in asynchronous processors. The novel feature of this mechanism is that it permits the presence of a data-dependent number of instructions in the execution pipeline of the processor. Finally, at the level of processor architecture, we present the architecture of a processor with an independent instruction stream for branches. The instruction set permits loops and function calls to be executed with minimal control-flow overhead.