Approaching the maximum energy saving on embedded systems with multiple voltages

Dynamic voltage scaling (DVS) is arguably the most effective energy reduction technique. The multiple-voltage DVS systems, which can operate only at pre-determined discrete voltages, are practical and have been well studied. However, one important unsolved problem is how many levels and at which values should voltages be implemented on a multiple-voltage DVS system to achieve the maximum energy saving. We refer this as the voltage set-up problem. In this paper, (1) we derive analytical solutions for dual-voltage system. (2) For the general case that does not have analytic solutions, we develop efficient numerical methods. (3) We demonstrate how to apply the proposed algorithms on system design. (4) Interestingly, the experimental results suggest that the multiple-voltage DVS system, when the voltages are set up properly, can reach DVS technique's full potential in energy saving. Specifically, on the design of an ad hoc application-specific system and the design of the MPEG video encoder, we find that the best single-voltage systems consume 150% and 20% more energy than the tight theoretical lower bounds, respectively. However, our approach gives dual-, 3-, and 4-voltage DVS system settings that are only 17.6%, 4.9%, and 2.6% for the ad hoc system, and 4.0%, 1.1%, and 0.2% for the MPEG video encoder, over the same lower bounds.