On removing redundancy in sequential circuits

A procedure of removing redundancy in large sequential circuits Is proposed. In this procedure, no global reset state is required and no state transition informa- tion is needed. A definition of sequential redundancy is first given. We show that if a fault is potentially undetectable (p- undetectable), it is sequentially redundant. An algorithm of identifying p-undetectable faults is then described. For large circuits, we propose a practical procedure to identify a subset, called feedback-free sequential redundant faults, of redun- dant faults. In this procedure, a minimal set of signals is selected and assumed fully controllable and observable to con- vert the given circuit into a feedback-free model. Redundan- cies in the feedback-free circuit model are then identified and removed. This procedure could also eliminate redundant flip-flops. Experimental results show that our method SUC- cessfully minimizes the signal count by about 8.4%, in aver- age, on six large MCNC benchmark sequential circuits with up to 20K gates and 1700 flip-flops. In some examples, up to 7.8% of the flip-flops is removed without changing the circuit's input/output behavior.