[Gumstix-users] Cpufreq on gumstix

[Craig H. <cr...@gu...>]

CPUFREQ is now included in the standard gumstix kernel.  This allows 
dynamic changing of the CPU frequency using the sysfs filesystem.

To change frequencies (simply), write the new CPU clock frequency to 
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed, eg:

# echo 398131 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
# echo 99533 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed

etc.  The valid values for cpu frequency are:

99533,132710,199066,265421,331776,398131,530842

Note that strictly speaking, you're not supposed to clock a 200MHz CPU 
over 200MHz, nor a 400MHz CPU over 400MHz.  It no doubt breaks some 
kind of warranty agreement.

You can also read up on the cpufreq governors and policies in the linux 
kernel source tree under Documentation/cpu-freq -- but it's not the 
best written of linux docs.

Benchmarks for some of these frequencies are on the Wiki -- please feel 
free to add more datapoints if they're relevant; please don't add more 
numbers for the same frequencies where your results are just off ours 
by 0.01%.  Also, we've got some basic power-draw numbers for the 
various frequencies, but I don't think we've posted them yet on the 
Wiki.  Basically though, slower = less power.

C