docs: Add hardware RPi PWM documentation (#4418)
Signed-off-by: Martin van Es <martin@mrvanes.com>
This commit is contained in:
parent
f24210054a
commit
4cf25c714a
|
@ -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|
|
||||
|
|
Loading…
Reference in New Issue