Software and Operating System Support

The basic goal of energy reduction from the software standpoint is to maximize the battery lifetime of portable general-purpose microprocessor devices by reducing the energy necessary to complete a given task without significantly changing system behavior. Software energy reduction techniques can be divided into two categories: static, which optimizes software before it is executed, and dynamic, which alters the operation of the device at run-time. Static energy reduction techniques for a microprocessor in a general-purpose system can be divided into two categories: high-level application design and compile-time optimization. Dynamic techniques rely on the software running in a portable electronic device to monitor and adjust the device operation at run-time. For example, a laptop that can turn off its LCD backlight requires a dynamic algorithm to determine when the backlight is not needed. Typically, dynamic techniques also require some modification to the base hardware, i.e. the ability to turn off the LCD display, which might not inherently reduce energy consumption. DVS is a dynamic technique that controls the speed of the CPU.