Optimal selection of supply voltages and level conversions during data path scheduling under resource constraints

In this paper we will consider how to select an optimal set of supply voltages and account for level conversion costs when optimizing the schedule of a resource dominated data path for minimum energy dissipation. An integer linear program (ILP) is presented for minimum energy schedules under latency, supply voltage, and resource constraints. The supply voltage assignment for each resource is modeled as fixed for all time. Schedules were generated for a variety of data path structures, resource and latency constraints. Resource constraints tended to limit the use of reduced supply voltages. With latency constraints loosened to 1.5× minimum latency, unlimited resources, and two power supplies, energy savings ranged from 53% to 70% compared to 5 V operation. When resource constraints were applied, savings dropped to a range of 46% to 58%. Loosened latency constraints resulted in increased use of lower supply voltages. With resource constraints un-changed and latency constraints of 2× minimum latency, energy savings increased to a range of 64% to 75%. In no case did three supplies decrease energy by more than 5% compared to two supplies