We present a new framework for checking safety failures. The approach is based on the conservative inference of the internal states of a system by the observation of the interaction with its environment. It is based on two similar mechanisms : forward implication, which performs the analysis of the consequences of an input applied to the system, and backward implication, that performs the same task for an output transition. While being a very simple approach, it is general and we believe it can yield efficient algorithms in different safety-failure checking problems. As a case study, we have applied this framework to an existing problem, the hazard checking in (speed-independent) asynchronous circuits. Our new methodology yields an efficient algorithm that performs better or as well as all existing algorithms, while being more general than the fastest one.

This paper proposes a synthesis method to obtain speed-independent asynchronous circuits directly from signal transition graph (STG) specifications with single cycle signals which can be non-persistent and have free-choice operations. The resulting circuits are implemented with basic gates and asynchronous latches, and operate correctly under finite but unbounded gate delays and the zero wire delay assumptions. The proposed method introduces 5 types of lock relations to implement a non-persistent STG. A non-persistent STG can be implemented if every non-persistent signal to a signal t is super-locked with t. The resulting circuits are optimized by extracting of literals, mapping onto asymmetric C-elements, etc. Experimental results show that the proposed synthesis method outperforms the existing synthesis systems such as SYN and SIS.