Adding PMU support for Apple PPC-based computers

[Peter Grehan]

> It has a G4 @ 533 MHz, but from dmesg I get:
> root at kg-g4# dmesg | grep cpu
> cpu0: Motorola PowerPC 7400 revision 2.9, 200.00 MHz

  Fixed in -CURRENT and RELENG_7 so will be picked up in the next beta.

later,

Peter.