Live long and prosper: Juggling performance and battery life in handheld systems

As the state-of-the-art in low-power CPUs races forward, CPUs become the most critical components in the design of handheld devices. New CPUs, such as Intel's XScale, Alchemy Semiconductor's Au 1000, and Transmeta's Crusoe, dynamically scale clock frequency and voltage. As power consumption varies linearly with clock speed and as the square of core voltage, engineers want to have hardware hooks to be able to adjust both clock speed and voltage as necessary, based on device performance. Taking full advantage of the low-power hardware features requires software control. The good news is that many of the operating systems in today's handheld devices have built-in APIs and other hooks that allow you to take advantage of the operating system's and CPU's lowpower modes. However, engineers may need to build their own software to fully implement the power-management features.