OMAP Wireless Connectivity CPU Clock Setup

CPU Clock

Both platforms AM18x and Am37x allow changing the CPU clock frequency (Improve performance, power saving, etc...).
To perform the CPU frequency change correctly, the following steps are required:

• Listing all the available frequencies of the board.
• Modifying the CPU frequency according to one of the frequencies in the list.
• querying the CPU frequency to make sure it has changed.

Following the above steps ensures that the CPU frequency is changed to the desired one.

Listing the available frequencies
This is done by invoking the command:

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

The command will list all the available CPU frequencies and issue output like:

456000 408000 372000 300000 200000 96000

The frequencies are in KHz units.

Modifying the CPU frequency
Assume we pick the 456000 (456MHz) frequency. To modify the CPU to that frequency we issue the command:

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

This command applies the frequency typed (456MHz).
Note:

If you try to change the frequency to frequency that doesn't exist in the list, the system will change the frequency to the nearest frequency to the one you requested.

For example, if we change the frequency to 372560 KHz, the system will change it to 372000 KHz as it is the nearest available frequency.

Querying the CPU frequency
Once we applied the CPU frequency, we need to check that the frequency actually changed. We do that by invoking:

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

The output might be something like:

456000

which is actually the frequency we picked up earlier.

CPU Frequencies

The table below shows the default and the maximum frequency for the current platforms.

Platform	Default frequency	Max frequency
AM18x	300000	456000
AM37x	600000	1000000

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