Signal Transition Graph Constraints for Synthesis of Hazard-Free Asynchronous Circuits with Unbounded-Gate Delays

A synthesis procedure for asynchronous control circuits from a high level specification, signal transition graph (STG), is described. In this paper, we propose some syntactic constraints on STG to guarantee hazard-free implementation. We have introduced a global persistency concept in order to establish the relationship between the persistency concept introduced by Chu [2] (which we call local persistency) and the consistent state coding (CSC). The STG syntactic constraints required to compute the input set of a signal are identified. We analyze all hazards under both single and multiple input change conditions and propose necessary changes to the net contraction and logic synthesis procedures. The proposed changes are guaranteed to generate hazard-free circuits with the unbounded-gate delay model, if the STG is live, safe and has consistent state coding. 1 1 Introduction Synthesis of asynchronous circuits is gaining popularity due to inherent clock distribution and clock skew prob..