pmu —
support for Power Management Units found in all Apple laptops
  and some desktop Power Macintosh computers
pmu* at obio?
nadb* at pmu?
battery* at pmu?
smartbat* at pmu?
The pmu driver provides support for the Power Management
  Unit found in Apple laptops and some desktop Power Macintosh computers.
  Functions controlled by the PMU include the real time clock, ADB, power,
  batteries, on some laptops like the PowerBook 3400c and similar machines it
  also controls hotkeys and display brightness, on others it provides an
  iic(9) bus and on some it controls
  CPU speed. On many older machines it also provides access to some non-volatile
  memory and thermal sensors. Not all those features are present on all
  machines, for instance Power Macintosh G4 and later machines don't have ADB,
  many more recent laptops have display brightness and backlight control built
  into the graphics controller instead of the PMU, only a few older PowerBooks
  use the PMU for CPU speed control and newer machines use a different way to
  access non-volatile memory. However, all known PMUs so far provide a real time
  clock and power control.
Real time clock and power control are present and supported on all machines that
  can run NetBSD/macppc, ADB is supported when present.
  - PowerBook
    2400, 3400c, and 3500
- Battery status and thermal sensors found on the mainboard and in the
      battery pack are supported by the
      battery(4) driver, values
      can be read via envsys(4).
      Hotkeys for brightness control are supported, CPU speed control and
      parameter RAM are present but unsupported.
- Power
    Macintosh G4
- ADB is not present, iic(9) is
      present but unsupported.
Some features are currently unsupported, like the
  iic(9) bus, access to parameter RAM
  and CPU speed control.