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Table of Contents
PWM
Introduction
This document mainly describes the usage of hardware PWM. You will learn how to control the hardware PWM on the 40-Pin Header.
PWM Information
VIM1
| PWM | PIN & GPIO Number | DT Overlays Node | Device Node |
|---|---|---|---|
| PWM_AO_A | PIN35 - GPIOAO_3 (#504) | pwm_ao_a | /sys/class/pwm/pwmchip4 |
VIM2
| PWM | PIN & GPIO Number | DT Overlays Node | Device Node |
|---|---|---|---|
| PWM_D | PIN35 - GPIODV_28 (#478) | pwm_d | /sys/class/pwm/pwmchip1 |
VIM3/3L
| PWM | PIN & GPIO Number | DT Overlays Node | Device Node |
|---|---|---|---|
| PWM_F | PIN35 - GPIOX_7 (#432) | pwm_f | /sys/class/pwm/pwmchip4 |
VIM4
| PWM | PIN & GPIO Number | DT Overlays Node | Device Node |
|---|---|---|---|
| PWM_F | PIN35 - GPIOY_8 (#482) | pwm_f | /sys/class/pwm/pwmchip4 |
Enabel PWM
In order to use the PWM, you need to enable the PWM function via Device Tree Overlay.
VIM1/2/3/3L/Edge1
Edit /boot/env.txt to add the pwm node to overlays node if it is not exist.
Take VIM3 as an example to enable PWM_F, you need to add pwm_f node to overlays node.
overlays=uart4 pwm_ao_a pwm_f
After reboot, you will see the pwm device node.
$ ls /sys/class/pwm/pwmchip4
device export npwm power subsystem uevent unexport
VIM4
Edit /boot/dtb/amlogic/kvim4.dtb.overlay.env to add pwm node to fdt_overlays node if it is not exist.
e.g. Enable PWM_F, you need to add pwm_f to node fdt_overlays.
fdt_overlays=pwm_f
After reboot, you will see the pwm device node.
$ ls /sys/class/pwm/pwmchip4
device export npwm power subsystem uevent unexport
Disable PWM to Use GPIO
If you want to use normal GPIO instead of PWM, you can remove the PWM node in device tree overlays configration file.
Control PWM
Enable PWM:
VIM1/3/3L/4
$ echo 1 | sudo tee /sys/class/pwm/pwmchip4/export $ echo 1000000 | sudo tee /sys/class/pwm/pwmchip4/pwm1/period $ echo 500000 | sudo tee /sys/class/pwm/pwmchip4/pwm1/duty_cycle $ echo 1 | sudo tee /sys/class/pwm/pwmchip4/pwm1/enable
VIM2
$ echo 1 | sudo tee /sys/class/pwm/pwmchip1/export $ echo 1000000 | sudo tee /sys/class/pwm/pwmchip1/pwm1/period $ echo 500000 | sudo tee /sys/class/pwm/pwmchip1/pwm1/duty_cycle $ echo 1 | sudo tee /sys/class/pwm/pwmchip1/pwm1/enable
Use an oscilloscope to check if the pins have been successfully enabled.
If you use an oscilloscope to view the PWM waveform, remember that the SBC and the oscilloscope need to share the same GND (ground).
Disable PWM:
VIM1/3/3L/4
$ echo 0 | sudo tee /sys/class/pwm/pwmchip4/pwm1/enable
VIM2
$ echo 0 | sudo tee /sys/class/pwm/pwmchip1/pwm1/enable