Battery-conscious task sequencing for portable devices including voltage/clock scaling

Operation of battery-powered portable systems can no longer be sustained once a battery becomes discharged. Maximization of the battery lifetime is a difficult task due to nonlinearity of battery behavior that depends on the characteristics of the system load profile. We address the problem of task sequencing without and with voltage/clock scaling that shapes the profile so that the battery lifetime is maximized. We developed an accurate analytical battery model and validated it with measurements taken on a real lithium-ion battery used in a pocket computer. We use the model as a basis for a unique battery-conscious cost function and utilize its properties to develop several novel algorithms, including insertion of recovery periods and voltage/clock scaling for delay slack distribution.