Evolution of asynchronous sequential circuits

Asynchronous systems are being viewed as an increasingly viable alternative to purely synchronous systems, due to their inherent benefits. At the same time, the complexities involved in such designs make manual designs challenging and suggest the use of evolutionary design procedures. Yet, surprisingly, there has not been an attempt so far to evolve asynchronous sequential circuits. This paper pioneers this attempt and proposes an evolutionary approach for the first time. The evolution is done at two levels using a developmental approach called the developmental Cartesian genetic programming (DCGP) technique. The first level evolution aims at evolving race-free stable circuits, satisfying the input/output combinations, with no hazards or minimal number of hazards. The second level evolution modifies/adds more components to the circuits, in order to make them hazard-free, both with respect to static as well as dynamic hazards. Experimental results for a modulo-six counter and an ISCAS'89 benchmark circuit, 'lion', are provided as a proof of concept.