SPFD-based effective one-to-many rewiring (OMR) for delay reduction of LUT-based FPGA circuits

This paper proposes an innovative method for SPFD-based rewiring in Look-Up-Table-based (LUT-based) FPGA circuits. The new method adds new input wires to two or more LUT's in order to remove or to replace a target wire. There have been a few rewiring methods for FPGA circuits so far, such as the original SPFD-based optimization sometimes called Local Rewiring (LR), SPFD-based Global Rewiring (GR) and SPFD-based Enhanced Rewiring (ER). However, all of them replace one wire with other new input wire to one LUT but not with those to two or more LUT's. Moreover, the LR removes or replaces input wires with new one to the same LUT only, and the GR and ER topologically limit the LUT's where new input wires are added. Our new method, called One-to-Many Rewiring (OMR), loosens such topological constraints for more flexible FPGA circuit transformation so that it is easier to import constraints on physical design to the logic optimization. The experimental results show our OMR can transform FPGA circuits more flexibly than the LR, GR and ER, by introducing the new manipulation, wire addition. The OMR can rewire 1.2 times as many wires as the existing methods, especially, the ER. The computation time is as short as the existing methods.