Scheduling and optimal voltage selection for low power multi-voltage DSP datapaths

We present an algorithm called MOVER (Multiple Operating Voltage Energy Reduction) to minimize datapath energy dissipation through use of multiple supply voltages. In a single voltage design, the critical path length, clock period, and number of control steps limit minimization of voltage and power. Multiple supply voltages permit localized voltage reductions to take up remaining schedule slack. MOVER initially finds one minimum voltage for an entire datapath. It then determines a second voltage for operations where there is still schedule slack. New voltages can be introduced and minimized until no schedule slack remains. MOVER was exercised for a variety of DSP datapath examples. Energy savings of up to 50% were observed when comparing dual to single voltage results. The benefit of going from two to three voltages never exceeded 15%. Circuit resource requirements for multiple voltages varied greatly. In some cases requirements changed very little with respect to number of voltages, but area penalties up to 150% were observed. Implications for IC layout are discussed.