Analyzing Isochronic Forks with Potential Causality

Asynchrony and concurrency are fundamental notions in the fields of asynchronous circuits as well as distributed systems. This paper treats asynchronous circuits as a special class of distributed systems. We adapt the distributed systems notion of potential causality to asynchronous circuits, and use it to provide a formal proof of the precise nature of the isochronic fork timing assumption in quasi delay-insensitive (QDI) circuits. Our proofs provide a transparent analysis that provides better intuition regarding the operation of QDI circuits. We build on our theory to rigorously establish several "folk theorems" about identifying isochronic forks in QDI circuits.