Setting CPU Speed¶

By default (and during u-Boot operation), the MityDSP-L138F family of SOMs initialize the CPU speed to 300 MHz. To set the CPU speed of commercial temperature modules to the maximum 456MHz, issue the following command:

echo 456000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed 

To check that is was set correctly, issue this:

cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

This will only work on commercial temp processors, since the industrial temp versions are limited to 372MHz. You can check your cpu's maximum speed by typing:

cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq

You can list all the available frequencies by typing:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies

Remember that the frequencies in these commands are in kHz, not MHz or Hz...

This information is based on the linux cpufreq subsystem, the capabilities mentioned above assume that you have enabled a cpufreq governor that supports modification of the cpu speed during runtime.

Also, Critical Link recommends that you set the CPU speed once prior to loading the FPGA (for modules that include an FPGA) as altering the CPU speed will cause the EMIFA clock (used by the FPGA framework) to stop and change frequency. DCM's connected to the FPGA may break lock during this interaction, and glitches in the clock distribution within the FPGA may occur.