Energy trade-offs in the IBM wristwatch computer

We recently demonstrated a high function wrist watch computer prototype that runs the Linux operating system and also XII graphics libraries. In this paper we describe the unique energy related challenges and tradeoffs we encountered while building this watch. We show that the usage duty factor for the device heavily dictates which of the powers, active power or sleep power, needs to be minimized more aggressively in order to achieve the longest perceived battery life. We also describe the energy issues that percolate through several layers of software all the way from device usage scenarios, applications, user interfaces, system level software to device drivers. All of these need to be systematically addressed to achieve the battery life dictated by the hardware components and the capacity of the battery in the device.