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International Journal of Reconfigurable Computing
Volume 2011, Article ID 972375, 16 pages
http://dx.doi.org/10.1155/2011/972375
Research Article

On Self-Timed Circuits in Real-Time Systems

Department of Computer Engineering, Embedded Computing Systems Group, Vienna University of Technology, Treitlstraße 3, 1040 Vienna, Austria

Received 6 August 2010; Accepted 8 January 2011

Academic Editor: Michael Hübner

Copyright © 2011 Markus Ferringer. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

While asynchronous logic has many potential advantages compared to traditional synchronous designs, one of the major drawbacks is its unpredictability with respect to temporal behavior. Having no high-precision oscillator, a self-timed circuit's execution speed is heavily dependent on temperature and supply voltage. Small fluctuations of these parameters already result in noticeable changes of the design's throughput and performance. Without further provisions this jitter makes the use of asynchronous logic hardly feasible for real-time applications. We investigate the temporal characteristics of self-timed circuits regarding their usage in real-time systems, especially the Time-Triggered Protocol. We propose a simple timing model and elaborate a self-adapting circuit which shall derive a suitable notion of time for both bit transmission and protocol execution. We further introduce and analyze our jitter compensation concept, which is a threefold mechanism to keep the asynchronous circuit's notion of time tightly synchronized to the remaining communication participants. To demonstrate the robustness of our solution, we perform different tests and investigate their impact on jitter and frequency stability.