MitySOM-335x Frequency Scaling¶
By default (and during u-Boot operation), the MitySOM-3359 family of SOMs initialize the CPU speed to 720 MHz. To set the CPU speed of commercial temperature modules to a speed lower than the maximum 720MHz please follow the directions below.
For testing that shows the impact of changing the CPU frequency of a module on current draw go here: http://support.criticallink.com/redmine/projects/armc8-platforms/wiki/MityARM-335x_Power_Supply_Requirements
Setting CPU speed through Linux with "Userspace" governor¶
Currently by default the Linux kernel is built to have the scaling governor configured for "performance". This means that you cannot change the frequency by echoing commands to the scaling registers. If the kernel is setup with the governor set in "userspace" mode than issues commands will work.
To check the current frequency or verify a change
Checking Current Governor Mode
Check Available Governor Modes
Check Available Frequencies
You can list all the available frequencies by typing:
Currently available frequencies are 275MHz, 500MHz, 600MHz and 720MHz.
Currently available frequencies are 300MHz, 600MHz, 720MHz and 800Mhz.
Currently available frequencies are 300MHz, 600MHz, 720MHz, 800Mhz and 1Ghz.
To Change the Frequency
You need to make sure governor is set to userspace otherwise the governor will change the speed back.
echo userspace > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor echo 275000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
Remember that the frequencies in these commands are in kHz, not MHz or Hz...
Setting CPU speed through userspace application (cpufrequtils)¶
If the governor mode is not set to "userspace" in the kernel it is possible to install a package that will allow for the modification of the CPU frequency through it.
With a valid internet connection (may need /etc/resolv.conf set with a "nameserver 10.0.0.1" line to setup your local dns server) issue the follow command:
opkg install cpufrequtils
Determine available frequencies
Set the desired speed (in MHz)
cpufreq-set -f 275
Verify that the frequency is was set
At this point you can return to the userspace echo commands to change the frequency.
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