Scheduling of Dual Supercapacitor for Longer Battery Lifetime in Systems with Power Gating

Abstract

The wake-up of power gating (PG) components leads to flow of in-rush current which quickly discharges the battery. An arrangement of instruction controlled hybrid battery-supercapacitor can enable longer battery life in systems with instruction controlled PG. The present work extends a battery-single supercapacitor system (B-SC) model to its equivalent battery-dual supercapacitor system (B-2SC) and shows that B-2SC can achieve higher longevity than its equivalent B-SC. Two instructions – disconnect battery (db) and connect battery (cb) have been introduced along with architectural support for B-2SC. The instruction db disconnects the battery from the PG components during wake-up. It also disconnects either one or both of the supercapacitors from the battery. Hence simultaneously either both supercapacitors can discharge or one can discharge while the other can be charged. Disconnecting the battery during wake-up minimizes rate capacity effect (C-rate) for longer battery life. The instruction cb connects the battery to the PG components and the supercapacitors. The db-cb scheduler inserts a db before an instruction which causes to wake-up of PG components. It places a cb in such a way that it executes after wake-up of all the desired the PG components. The efficacy of the proposed method is evaluated on MiBench and MediaBench benchmark programs. B-SC and B-2SC reduce C-rate by an average of 14.25% and 21.87%, respectively with corresponding average performance loss of 6.87% and 9.25%.