Texas Instruments AM335 Series Design Manual page 19

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To manually set the OPP, first you must be in userspace governor. Then write the desired MPU
frequency:
$ echo 600000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
Linux also offers a way to bound the frequency range of the scaling governors. Use scaling_min_freq and
scaling_max_freq to set the minimum and maximum frequencies to which the CPU will scale. The
following command would cap MPU speed at 600 MHz.
$ echo 600000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
3.2.2 CPU Idle Interface
During periods where the MPU is inactive, the CPUIdle driver will place the MPU in a low power state, as
determined by the CPUIdle governor. The governor is called whenever the idle loop is called, which
happens when the Linux thread scheduler has no more tasks to run.
For information regarding CPU Idle Linux kernel driver of the most recent release, and an archive of
previous releases, see the
The availability of CPUIdle governor is determined by your kernel configuration. There are no necessary
actions to enable CPUIdle, so long as it is enabled in the kernel, it operates transparently in the
background.
CPUIdle offers a sysfs entry that provides some statistics on the usage of each of the idle states:
root@am335x-evm:~#
-r--r--r-- 1 root
-rw-r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
root@am335x-evm:~#
-r--r--r-- 1 root
-rw-r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
-r--r--r-- 1 root
3.2.3 System Suspend
Using the CM3 module on the AM335x, it is possible for the system to go into DeepSleep0 (DS0) or a
suspend state where many peripherals are powered down. In DS0, all peripherals except for those in the
PM_WKUP domain will be powered off. For a list of the peripherals in this domain, see
When in DS0, the following are valid wakeup sources for the AM335x GP EVM:
• UART0
• GPIO0
• Touchscreen
To enter DS0:
$ echo mem > /sys/power/state
To enter suspend:
$ echo standby > /sys/power/state
The PM driver will notify the user if there was an issue entering either of these states.
SPRAC74A – February 2017 – Revised March 2017
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Linux_Core_Power_Management_User's_Guide
ls -l /sys/devices/system/cpu/cpu0/cpuidle/state0
root 4096 Dec 20 16:49 desc
root 4096 Dec 20 16:49 disable
root 4096 Dec 20 16:49 latency
root 4096 Dec 20 16:49 name
root 4096 Dec 20 16:49 power
root 4096 Dec 20 16:49 residency
root 4096 Dec 20 16:49 time
root 4096 Dec 20 16:49 usage
ls -l /sys/devices/system/cpu/cpu0/cpuidle/state1
root 4096 Dec 20 16:49 desc
root 4096 Dec 20 16:49 disable
root 4096 Dec 20 16:49 latency
root 4096 Dec 20 16:49 name
root 4096 Dec 20 16:49 power
root 4096 Dec 20 16:49 residency
root 4096 Dec 20 16:49 time
root 4096 Dec 20 16:49 usage
Copyright © 2017, Texas Instruments Incorporated
Linux Power Optimization Features
wiki page.
Section 3.3.3.1.
AM335x Low Power Design Guide
19