On Tue, Jan 18, 2005 at 12:28:26PM -0500, Tim Kelly wrote:
> > (1.33 GHz, but 668.73 MHz according to dmesg
> >(why?))

Oh.  I missed the referent for "why?"...  Most (all?) powerbooks
can run at reduced speed to save power.  This is exposed as "maximize
performance" or "maximize battery" or something like that in the
Energy control panel.  The two speeds are defined by the PLL inputs
to the CPU.  Those are generated by the bridge chip, I believe,
and can be reconfigured, but the CPU has to be reset to use the
new PLL values.  To change speeds, you basically have to put the
system to sleep with a slightly different command than you would
for putting it to sleep.  The same hardware is responsible, and
the software support is basically the same:

	* save all state information
	* shutdown all hardware units
	* send command to change cpu speed or go to sleep
when the cpu starts up again,
	* restore power to hardware units
	* look for any hardware changes
	* restore all state information
	* handle any mismatch between current hardware and old state
	  info.  (e.g., "my root partition is now gone!")

Or something close to that, anyway.  This is old information, but
I doubt it's changed much.

-allen

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