6ul 4.9 cpufreq

The i.MX6UL CPU has a number of power management features to scale the CPU speed. The maximum speed of the i.MX6UL is 696 MHz; other frequencies possible are 528 MHz, 396 MHz, and 198 MHz. By default, the "ondemand" frequency governor is used. This allows the CPU to run at its lowest speed and increase it when there is computation demand. Other governors are available, see the kernel documentation for a list of these governors and their operation.

The current CPU frequency as well as the governor used are modified by a set of files within the folder "/sys/bus/cpu/devices/cpu0/cpufreq". Some key files are outlined below:

 /sys/bus/cpu/devices/cpu0/cpufreq/cpuinfo_cur_freq - Lists the current frequency
 /sys/bus/cpu/devices/cpu0/cpufreq/scaling_governor - Lists/sets the current frequency governor
 /sys/bus/cpu/devices/cpu0/cpufreq/scaling_setspeed - When govenor is "userspace", set current frequency
 /sys/bus/cpu/devices/cpu0/cpufreq/scaling_available_frequencies - List all available frequencies
 /sys/bus/cpu/devices/cpu0/cpufreq/scaling_available_governors - List all available governors

In order to manually specify a frequency, the frequency governor must be set to userspace. For example, to force the lowest CPU frequency all the time:

echo "userspace" > /sys/bus/cpu/devices/cpu0/cpufreq/scaling_governor
echo "198000" > /sys/bus/cpu/devices/cpu0/cpufreq/scaling_setspeed