Unable to get PWM output

• 

  kornpow

  Posts: 12

  Joined: 2024-08-12 19:16

  2025-05-22 21:27

  Device: Luckfox Pico Pro Max
  
  PWM Device: PWM5_M1, Pin 72
  
  I am trying to get PWM to work on my device, but even though I am confident I have followed instructions correctly, I am not getting any PWM output.
  
  I am able to export the PWM5 pin, which then gives me the additional PWM properties:
  ```
  [root@luckfox ]# ls /sys/class/pwm/pwmchip5/pwm0
  capture enable period power
  duty_cycle output_type polarity uevent
  ```
  
  I am sure it is enabled, and configured:
  ```
  [root@luckfox ]# cat /sys/class/pwm/pwmchip5/pwm0/enable
  1
  [root@luckfox ]# cat /sys/class/pwm/pwmchip5/pwm0/period
  1000000
  [root@luckfox ]# cat /sys/class/pwm/pwmchip5/pwm0/duty_cycle
  100000
  ```
  
  However, when I put a multimeter probe (I know, not the best tool) on the pin, it seems to sit, unwavering, at the tri-state voltage of approx 0.7V. No matter what duty cycle or period I configure, nothing changes on the output. I have the output hooked up to an LCD screen backlight, and the backlight never changes.
  
  As a sanity check, I manually implemented PWM using python-periphery and GPIO, and I am able to affect the brightness of the screen, and the multimeter reflected the change in duty cycle.
  
  I am running a buildroot OS that I built myself, but I didn't modify any device trees. SPI and GPIO are working just fine. I've turned off all peripherals which might be affecting the output.
  
  Please, can I get some help? Thank you.
  
  /etc/luckfox.cfg
  ```
  SPI0_M0_CS_ENABLE=1
  SPI0_M0_MODE=1
  SPI0_M0_STATUS=1
  SPI0_M0_MISO_ENABLE=0
  SPI0_M0_SPEED=40000000
  CSI_ENABLE=1
  UART4_M1_STATUS=0
  PWM11_M1_STATUS=0
  PWM10_M1_STATUS=0
  PWM9_M1_STATUS=0
  PWM8_M1_STATUS=0
  PWM0_M1_STATUS=0
  PWM11_M2_STATUS=0
  I2C3_M1_STATUS=0
  I2C3_M1_SPEED=0
  I2C1_M1_STATUS=0
  I2C1_M1_SPEED=0
  PWM5_M1_STATUS=1
  UART1_M1_STATUS=0
  UART3_M1_STATUS=0
  UART0_M1_STATUS=0
  ```

  • Quote

$pwm5 {
	status = "okay";
	pinctrl-names = "default";
	pinctrl-0 = <&pwm5m1_pins>;
	
};