On Self-Timed Circuits in Real-Time Systems

While asynchronous logic has many potential advantagescompared to traditional synchronous designs, one of themajor drawbacks is its unpredictability with respect to temporalbehavior. Having no high-precision oscillator, a self-timed circuit'sexecution speed is heavily dependent on temperature andsupply voltage. Small fluctuations of these parameters alreadyresult in noticeable changes of the design's throughput andperformance. Without further provisions this jitter makes the useof asynchronous logic hardly feasible for real-time applications. We investigate the temporal characteristics of self-timed circuitsregarding their usage in real-time systems, especially theTime-Triggered Protocol. We propose a simple timing model andelaborate a self-adapting circuit which shall derive a suitablenotion 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 asynchronouscircuit's notion of time tightly synchronized to the remainingcommunication participants. To demonstrate the robustness ofour solution, we perform different tests and investigate theirimpact on jitter and frequency stability