Analysis of State Corruption caused by Permanent Faults in WCHB-based Quasi Delay-Insensitive Pipelines

Abstract

Quasi delay-insensitive asynchronous circuits have the appealing property of stopping further operation in case of a permanent fault. This fail-stop behavior makes them attractive for on-line repair: after removal of the permanent fault, the circuit can, ideally, continue operating without the need for state recovery. However, it has been shown that in certain cases the state may get corrupted before the operation actually stops. In this paper we use the example of a weak-conditioned half- buffer template to investigate more closely which situations can lead to such state corruption. We explore implementation variants like double completion detection to mitigate that undesired effect. Based on extensive gate-level simulation experiments we quantify the probability for state corruption seen in the different circuits and identify the relevant dependences. As it turns out, the proposed extensions can reduce, but not completely eliminate, the risk of state corruption. At the same time detection of illegal code words promises to have great potential for countermeasures.