From: Matt Robbins <mer34@co...> - 2008-05-22 22:52:26
What is the status of frequency scaling support for the Verdex? I'm
quite new to playing around with kernels, but I've collected the
I see that by default the relevant modules don't get built, and there
is no user-space interface (/sys/devices/system/cpu/cpu0/cpufreq/*).
However, there does seem to be some kind of adaptive behavior
happening: at idle (with an audiostix + tweener attached) I'm drawing
around 130 mA, but when in a tight loop, consumption goes up to nearly
I rebuilt the kernel with support for frequency scaling, and building
every governor as a module, and upon boot-up (really slow), my power
consumption dropped to 100 mA. However, loading the various governors
seemed to have no effect, and even when in a tight processing loop,
power consumption stayed at at around 100 mA. Querying the /sys
information, I see that the min, max and current frequency are all set
to 500 - something (can't quite remember), however I suspect that this
isn't the case, since the system is quite noticeably sluggish.
This leads me to believe that in the default configuration, something
in the kernel is switching the cpu from "run mode" to "turbo mode"
because I see the drastic change in power when I do not with frequency
scaling enabled (which I suspect sets the frequency to the lowest
setting). I'm guessing this because on boot up I see this kernel info
message: (coming from "arch/arm/mach-pxa/pxa25x.c" I believe)
> Run Mode clock: 208.00MHz (*16)
> Turbo Mode clock: 624.00MHz (*3.0, active)
For my application (long-term acoustic monitoring) it would be very
nice to be able to throttle down further, since most of the time the
system doesn't need to do much. Does anyone know what's going on
here? and if it is indeed a kind of dynamic switching between run and
turbo modes, does anyone know how to change the default clock speeds
for each of these modes, programmatically set the mode, or even query
which mode i'm in? I hope this is a meaningful explanation of my
problem. I've tried to do as much digging as I can, but I haven't
been able to learn much about this (at least with my current level of
expertise) Any help would be greatly appreciated.
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