Global SPFD Based Rewiring

In this paper we present the theory and the algorithms for global SPFD-based logic restructuring (GSPFD), which allows us to replace a target wire globally in the circuit (by some wire possibly far away from the target). It successfully overcomes the limitation of the existing SPFD-based rewiring methods that can only replace a wire with another having the same destination node. As a result, our method combines the advantages of both the ATPG-based logic restructuring method (which allows global rewiring) and the SPFD-based logic restructuring method (which allows the modification of node functions during rewiring), yet overcomes their limitation. We apply the G-SPFD algorithm to post-mapping re-synthesis for LUTbased FPGAs. Extensive experimental results show that it produces considerably better results (in terms of area or delay reduction) compared to the ATPG-based method and the SPFD-based method. The runtime of the G-SPFD algorithm is only slightly larger than that of the SPFD-based method, but is over 14X faster than that of the ATPG-based method. Furthermore, we show that when combined with the state-of-art logic partitioning method, our G-SPFD algorithm scales well to large circuits with little or no quality degradation.