You can use the linux cpufreq driver to do this. The cpufreq module
is disabled by default on the gumstix, due to the errata on the PXA
CPU which causes problems when it's used. See the PXA255 errata
manual for details. Basically, when you switch CPU core frequencies,
the states of many of the PXA controllers go to la-la land. In
practice, it looks like this doesn't always happen -- it seems to
happen though and cause all sort of problems when using something
like the "ONDEMAND" governor in cpufreq, where the core frequency is
being changed on a rapid and regular basis. I would hazard to guess
that using the USERSPACE governor, with suitable error checking after
switching frequencies (and probably also using it in combination with
the sa1100_wdt driver) would allow you to do what you want. In
practice, the "correct" answer is probably to rewrite the drivers
which depend on the various controllers which might lose state during
freq switch, so that they can recover from the state loss, if at all
possible. Not sure if that's possible though for all of the
On Jun 20, 2005, at 7:26 AM, Felix Nielsen wrote:
> Is it possible to change the MHz/clock from the application?
> Let's say I have a 400Mhz board, can I decrease the clock when I am
> "done" calculating stuff?
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