pezi
Raspberry Pi Model 4B PWM Error
The documentation in the README (the link) for setting up the Raspberry Pi Model 4B, so that it can run successfully using the dart_periphery package, appears to be incomplete. For example, after a reboot on my Raspberry Pi Model 4B, I would get a pwm error when opening pwmchip0, pwm0 and pwm1 channels. The next time or two restarting in debug mode it would start working. Upon investigation, the issue was with the /etc/udev/rules.d/99-pwm.rules file and with the dtoverlay file. When the Pi would boot up, the pwmchip0 did not have pwm0 and pwm1 exported.
Note that the Model 4 only has two pwm channels on pwm0. You can only use GPIO 12,13,18 or 19 for PWM. I am using GPIO 12 and 13. In the link about how to setup the pwm there are other dtoverlays but I have not tested all of them.
Here is My Solution
Step One: Update the config.txt
Use this dtoverlay in config.txt
dtoverlay=pwm-2chan,pin=12,func=4,pin2=13,func2=4
Step Two: Update the udev rule file
Open the file, and you will probably only see: SUBSYSTEM=="pwm", GROUP="gpio", MODE="0660"
sudo nano /etc/udev/rules.d/99-pwm.rules
Copy and paste the two ACTION lines under the SUBSYSTEM line.
SUBSYSTEM=="pwm", GROUP="gpio", MODE="0660"
ACTION=="add", SUBSYSTEM=="pwm", KERNEL=="pwmchip0", RUN+="/bin/sh -c 'echo 0 > /sys/class/pwm/pwmchip0/export'"
ACTION=="add", SUBSYSTEM=="pwm", KERNEL=="pwmchip0", RUN+="/bin/sh -c 'echo 1 > /sys/class/pwm/pwmchip0/export'"
After saving the file, reload the udev rules.
sudo udevadm control --reload-rules && sudo udevadm trigger
You will need to reboot.
Step Three: verify that pwmchip0 exported pwm0 and pwm1.
This command will check that pwm0 has been exported. If you do not see this, then retrace your steps and try again.
ls /sys/class/pwm/pwmchip0
You should see this response.
device export npwm power pwm0 pwm1 subsystem uevent unexport
Step Four: Run Flutter App with dart_periphery
On the Raspberry Pi Model 4B the only valid options are pwm(0,0) and pwm(0,1) These steps fixed the issue for me.
