UM0851 datasheet(237/245 Pages) STMICROELECTRONICS

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UM0851

Power management section

Doc ID 16604 Rev 2

237/245

that if the CPU usage needs to be below 20% between samples to have the frequency

decreased. For example to set the down threshold to 30% you would do the following.

echo 30 > /sys/devices/system/cpu/cpu0/cpufreq/conservative/down_threshold

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sampling_rate - same as ondemand

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sampling_rate_(min|max) - same as ondemand

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up_threshold - same as ondemand

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ignore_nice_load - same as ondemand

Performance governor

The CPU runs at maximum frequency regardless of the load.

echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

Powersave governor

The CPU runs at a minimum frequency regardless of the load.

echo powersave > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

CPUfreq stats about your CPU

The CPUfreq module lists stats about your CPU. These will help you find out things like the

current frequency of your processor or what available frequencies your CPU can scale to.

●

cpuinfo_cur_freq - Show the current frequency of your CPU(s). You can also find this

out by doing a "cat /proc/cpuinfo".

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

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cpuinfo_max_freq - Show the maximum frequency your CPU(s) can scale to

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

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cpuinfo_min_freq - Show the minimum frequency your CPU(s) can scale to.

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

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scaling_cur_freq - Show the available frequency your CPU(s) are currently scaled to.

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

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scaling_driver - Show the cpufreq driver the CPU(s) are using.

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

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scaling_max_freq - Set the maximum frequency your CPU(s) are allowed to scale to.

Look at the output from scaling_available_frequencies above. Then you can pick one of

those numbers (frequencies) to set to be the maximum frequency the CPU(s) are

allowed to scale to.

In SPEAr the range of scaling_available_frequencies is { 166 MHz, 266 MHz, 333 MHz}

so you might set this to 166000. So when the CPU frequency scales, it only goes to a

max of 166000 and not 333000. An example on how to set this would be the following

echo 166000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq

●

scaling_min_freq - Same as scaling_max_freq but setting a lower frequency limit that

the CPU(s) are not allowed to go below. For example:

echo 266000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq

This does not allow the CPU to go below the frequency of 266 MHz.

UM0851 Datasheet(PDF) 237 Page - STMicroelectronics

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