Device discovery and power management in embedded systems
This paper covers issues in device discovery and power management in embedded Linux systems. In particular, we focus on the IBM PowerPC 405LP (a "system-on-chip" CPU designed for handheld applications) and IBM's PDA reference design based upon it. Peripherals in embedded systems are often connected in an ad-hoc manner and are not on a bus which can be scanned or probed. Thus the kernel must have knowledge of what devices are present built in at compile time. We examine how the new unified device model provides a clean method for representing this information, while allowing good re-use of code from machine to machine. The 405LP includes a number of novel power management features, in particular the ability to very rapidly change CPU and bus frequencies. We also examine how the device model provides a framework for representing constraints the peripherals and their interconnections place upon allowable frequencies and other information relevant to power management.