Reconfigurable Constant Multiplication for FPGAs

This paper introduces a new heuristic to generate pipelined run-time reconfigurable constant multipliers for field-programmable gate arrays (FPGAs). It produces results close to the optimum. It is based on an optimal algorithm which fuses already optimized pipelined constant multipliers generated by an existing heuristic called reduced pipelined adder graph (RPAG). Switching between different single or multiple constant outputs is realized by the insertion of multiplexers. The heuristic searches for a solution that results in minimal multiplexer overhead. Using the proposed heuristic reduces the run-time of the fusion process, which raises the usability and application domain of the proposed method of run-time reconfiguration. An extensive evaluation of the proposed method confirms a 9%-26% FPGA resource reduction on average compared to previous work. For reconfigurable multiple constant multiplication, resource savings of up to 75% can be shown compared to a standard generic lookup table based multiplier. Two low level optimizations are presented, which further reduce resource consumption and are included into an automatic VHDL code generation based on the FloPoCo library.