Using asymmetric cores to reduce power consumption for interactive devices with bi-stable displays

Low power "helper" cores have been increasingly included on application processors to accomplish low intensity tasks such as music playing and motion sensing with minimum energy consumption. Recently, Guimbretière et al. [1] demonstrated that such helper cores can also be used to execute simple user interface tasks. We revisit this approach by implementing a similar system on an off-the-shelf application processor (TI OMAP4). Our study shows that in the case of high event rate interactions (pen inking and virtual keyboard), significant battery life gains (×1.7 and ×2.3 respectively) can be achieved with the helper core executing the interface. Having the helper core only dis-patch input events incurs a 18% penalty relative to the maximum savings rate, but allows for simplified deployment since it merely requires a change in toolkit infrastructure.