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| -rw-r--r-- | docs/RPi_microcontroller.md | 36 |
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diff --git a/docs/RPi_microcontroller.md b/docs/RPi_microcontroller.md index bc8d0fad..2229ee69 100644 --- a/docs/RPi_microcontroller.md +++ b/docs/RPi_microcontroller.md @@ -154,3 +154,39 @@ gpiochip1 - 8 lines: line 6: unnamed unused input active-high line 7: unnamed unused input active-high ``` + +Optional: Hardware PWM +======================================= +Raspberry Pi's have two PWM channels (PWM0 and PWM1) which are exposed on the header or if not, can be routed to existing gpio pins. +The Linux mcu daemon uses the pwmchip sysfs interface to control hardware pwm devices on Linux hosts. +The pwm sysfs interface is not exposed by default on a Raspberry and can be activated by adding a line to ```/boot/config.txt```: +``` +# Enable pwmchip sysfs interface +dtoverlay=pwm,pin=12,func=4 +``` +This example enables only PWM0 and routes it to gpio12. If both PWM channels need to be enabled you can use ```pwm-2chan```. + +The overlay does not expose the pwm line on sysfs on boot and needs to be exported by echo'ing the number of the pwm channel to ```/sys/class/pwm/pwmchip0/export```: +``` +echo 0 > /sys/class/pwm/pwmchip0/export +``` +This will create device ```/sys/class/pwm/pwmchip0/pwm0``` in the filesystem. +The easiest way to do this is by adding this to ```/etc/rc.local``` before the ```exit 0``` line. + +With the sysfs in place, you can now use either the pwm channel(s) by adding the following piece of configuration to your ```printer.cfg```: +``` +[output_pin caselight] +pin: host:pwmchip0/pwm0 +pwm: True +hardware_pwm: True +cycle_time: 0.000001 +``` +This will add hardware pwm control to gpio12 on the Pi (because the overlay was configured to route pwm0 to pin=12). + +PWM0 can be routed to gpio12 and gpio18, PWM1 can be routed to gpio13 and gpio19: +|PWM|gpio PIN|Func| +|---|--------|----| +| 0| 12| 4| +| 0| 18| 2| +| 1| 13| 4| +| 1| 19| 2| |