Input/Output-Interlocking for Fault Mitigation in QDI Pipelines

Abstract

In asynchronous \ac{QDI} circuits, temporal masking is a serious concern because of their event-driven behavior, which makes them prone to environmental effects: Data acceptance windows, e.g.\ are defined by transitions (token/acknowledgement) alone, without temporal bounds, therefore a glitch occurring anytime throughout such a window cannot be distinguished from an expected, correct transition in a straightforward manner and hence threatens data integrity. Therefore, shortening that window is one proposed way in the literature to enhance temporal masking in \ac{QDI} designs.

We examine a variant of the \ac{WCHB} called Interlocking \ac{WCHB} (which wisely shortens the transition window) because of its glitch filtering properties and a low cost implementation as compared to other variants. We propose modifications that enhance its dealing with illegal token words specifically when waiting for acknowledgment signal transitions in the so-called bubble limited operation mode. A very strict triple-check input filter with a glitch filter preventing the buffer from capturing an illegal state is used, which also enhances the deadlocking rate of the circuitry.