PXA Idle state, reduce clock ?

["Williams, Richard" <Richard.Williams@xxxxxxxxxxxxxxxxxxx>]

I'm trying to build low power system. I already have PXA sleep working
pretty well, allowing my applications to be slept ---- woken up and
recover to their pre-sleep state. Now I'm looking into extending the
period of the PXA idle. My system spends long periods nearly idle. I
feel that I can squeeze a little more power savings if I can extend the
idle time, and I want to reduce the clock frequency during idle periods.


I have modified the default_idle() function to extend the period of the
processor idle. I did this by modifying the OSMR0 timer register. I also
enabled all the external interrupts to bring the processor out of idle.
This seems to work pretty well. The processor idle time gets extended to
many seconds, but any external event brings the processor back almost
instantly. Now to reduce power further, the Intel manual says to insure
that the clock speed is reduced to minimum prior to going into idle
state.

I've tried putting a call to cpufreq_set() into the default_idle() code,
but I always get an OOPS when the code executes. I've tried yanking the
clock manipulation assembler code out and pasting it into the
default_idle(), but that OOPS also. From inside the default_idle() code,
prior to putting the processor into idle mode, how can I set the clock
to minimum ?

Thanks,

Rich

----------------------------
Richard B. Williams
Vitronics, Inc.
An MTC Technologies Company
3 Corbett Way
Eatontown, NJ 07724-2262
732-389-0244 x29
Richard.Williams@xxxxxxxxxxxxxxxxxxx

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