Power management and device discovery on 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 abilty 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.
