Analyzing Isochronic Forks with Potential Causality

Rajit Manohar and Yoram Moses

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.