PWM

Symbol Explanation

SDK$: Refers to the source code path.
console$: Generally refers to the command-line console of the motherboard.
ADB$: Android Debug Bridge command-line tool, generally refers to an environment where ADB can be run.

The Extend 40Pin interface contains multiple channels of PWM. The specific pins are shown in the Expansion Pin Section.

The following uses PWM2_CH7_M2 as an example for explanation.

For pwmX_Ych_Z, X represents the controller ID, Y represents the total number of channels supported by the current controller, and Z represents the channel ID.

PWM2_CH7_M2 represents:

pwm0_2ch_1: pwm@27331000
pwm2_8ch_6: pwm@2ade6000
pwm2_8ch_7: pwm@2ade7000

List relevant PWM nodes:

$ ls /sys/class/pwm/
pwmchip0  pwmchip1  pwmchip2  pwmchip3

You can view the corresponding PWM DTS nodes:

$ cat /sys/class/pwm/pwmchip0/device/uevent | grep FULLNAME
OF_FULLNAME=/pwm@27331000

It indicates that pwnchip0 corresponds to PWM0 Channel 1.

Configure the PWM channel:

Example: Set PWM0_CH1 channel, with a period of 10000ns, a duty cycle of 5000ns, and the polarity as normal.

$ echo 0 > /sys/class/pwm/pwmchip0/export
$ echo 10000 > /sys/class/pwm/pwmchip0/pwm0/period
$ echo 5000 > /sys/class/pwm/pwmchip0/pwm0/duty_cycle
$ echo normal > /sys/class/pwm/pwmchip0/pwm0/polarity
$ echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable

After the configuration parameters are successfully set according to the example, you can use a multimeter to measure the PWM0 pin. The correct voltage should be around 1.6V.

Export the PWM channel:

echo 0 > /sys/class/pwm/pwmchip0/export

Set the PWM period (frequency):

echo x > /sys/class/pwm/pwmchip0/pwm0/period

Set the PWM duty cycle:

echo x > /sys/class/pwm/pwmchip0/pwm0/duty_cycle

Set the PWM polarity:

echo normal > /sys/class/pwm/pwmchip0/pwm0/polarity
echo inverted > /sys/class/pwm/pwmchip0/pwm0/polarity

Enable PWM output:

echo 1/0 > /sys/class/pwm/pwmchip0/pwm0/enable

Last updated 4 days ago