rover-pi/pwm.md

Getting the PWM working

The Raspberry Pi zero (1 and 2) have 2 PWM peripherals, allowing you to pulse pins without the CPU doing any additional work. This is particuarly useful for controlling motor speeds when connected to a motor driver/H-bridge chip.

References

• Raspberry Pi Official Overlays information (github)
  • Line 4235 starts the description of the "pwm" overlay configuration
• Adding Basic Audio Ouput to Raspberry Pi Zero

Important Points

1. The gpio program is no longer available. It has been replaced with pinctrl which works a little differently.

Discussion

My raspberry pi zero W 2 wasn't working reliably with the PWM.

The gpio command has been depricated and is now replaced by the pinctrl commend. Running it did not list any PWM0 on any of the pins, which was concerning.

This forum post indicated the need for a pwm-2chan device tree overlay to get it to show up. After adding dtoverlay=pwm-2chan to the config.txt:

$ pinctrl
 0: ip    -- | hi // ID_SDA/GPIO0 = input
 1: ip    -- | hi // ID_SCL/GPIO1 = input
 2: a0    -- | hi // GPIO2 = SDA1
 3: a0    -- | hi // GPIO3 = SCL1
 4: op -- -- | hi // GPIO4 = output
 5: ip    -- | hi // GPIO5 = input
 6: ip    -- | hi // GPIO6 = input
 7: op -- -- | hi // GPIO7 = output
 8: op -- -- | hi // GPIO8 = output
 9: a0    -- | lo // GPIO9 = SPI0_MISO
10: a0    -- | lo // GPIO10 = SPI0_MOSI
11: a0    -- | lo // GPIO11 = SPI0_SCLK
12: ip    -- | lo // GPIO12 = input
13: ip    -- | lo // GPIO13 = input
14: ip    -- | lo // GPIO14 = input
15: ip    -- | hi // GPIO15 = input
16: ip    -- | lo // GPIO16 = input
17: ip    -- | lo // GPIO17 = input
18: a5    -- | lo // GPIO18 = PWM0
19: a5    -- | lo // GPIO19 = PWM1

Which looks much better. There is a pwm chip in /sys/class/pwm

After running the lgpio/pwm-test.py the pin is back to being listed as an input, so I'm confused. The PWM pin (under load) did the right values. Without a load on the Analog Discovery 2, I just saw noise.

I commented out dtoverlay=pwm-2chan and lgpio/pwm-test.py worked. The pwm chip is missing from /sys/class/pwm so I'm guess that's not needed.