On the Effects of Permanent Faults in QDI Circuits - A Quantitative Perspective

With their event-driven nature, quasi-delay-insensitive (QDI) asynchronous circuits offer a compelling fail-stop behavior along with an inherent 100 % permanent fault detection coverage. In fact, permanent faults break the handshake, pushing the circuit into deadlock. In this paper we give quantitative results for the relative occurrence of the different effects that can manifest in a QDI circuit due to permanent faults. We study in which and how many cases the state of the circuit gets corrupted before reaching the deadlock. This behavior diagnosis enables us to identify the cases in which the circuit can go back to operating normally if a (self-) repair process were to take place. This investigation is conducted through extensive fault injection experiments in a chosen circuit simulation. Stuck-at faults are injected on a gate-level VHDL model of the circuit, with a wide coverage of parameters.