rockpi 4 pwm overlay code
to create pwm overlay call :
dtc -O dtb -o rockchip-pwm-gpio.dtbo -b 0 -@ rockchip-pwm-gpio.dts
and move dtbo to /boot/dtc/rockchip/overlays
to activate overlay, modify /boot/armbianEnv.txt by adding:
overlay_prefix=rockchip
overlays=pwm-gpio
before PWM can be used, it should be initialized by calling
sudo echo 0 > /sys/class/pwm/pwmchip1/export
to use it from regular user account without sudo priviliges, some steps must be taken during or after system startup :
1. set ownership of the pwmchip1 and pwmchip2 and all it's descriptors to digital group
chown -R :digital /sys/class/pwm/pwmchip1/
chown -R :digital /sys/class/pwm/pwmchip2/
2. add rw priviliges to export/unexport descriptors
find /sys/class/pwm/pwmchip1/ -name export -exec chmod g+rw {} \;
find /sys/class/pwm/pwmchip1/ -name unexport -exec chmod g+rw {} \;
find /sys/class/pwm/pwmchip2/ -name export -exec chmod g+rw {} \;
find /sys/class/pwm/pwmchip2/ -name unexport -exec chmod g+rw {} \;
3. initialize PWM with export
echo 0 > /sys/class/pwm/pwmchip2/export
echo 0 > /sys/class/pwm/pwmchip2/export
4. set ownership of all new parameters to digital groups
chown -R :digital /sys/class/pwm/pwmchip1/
chown -R :digital /sys/class/pwm/pwmchip2/
5. add rw priviliges to PWM parameters ( duty_cycle enable period polarity power uevent )
find /sys/class/pwm/pwmchip1/ -name "duty_cycle" -exec chmod g+rw {} \;
find /sys/class/pwm/pwmchip1/ -name "enable" -exec chmod g+rw {} \;
find /sys/class/pwm/pwmchip1/ -name "period" -exec chmod g+rw {} \;
find /sys/class/pwm/pwmchip1/ -name "polarity" -exec chmod g+rw {} \;
find /sys/class/pwm/pwmchip1/ -name "power" -exec chmod g+rw {} \;
find /sys/class/pwm/pwmchip1/ -name "uevent" -exec chmod 0660 {} \;
to control PWM without sudo, particular user should be added to digital group:
sudo usermod -a -G digital <USERNAME>
after this, to control FAN SPEED via PWM use pwmset and pwmsts scripts
example :
pwmset 45 - set PWM speed to 45%
pwmsts
45