# RPi microcontroller
This document describes the process of running Klipper on a RPi and
use the same RPi as secondary mcu.
## Why use RPi as a secondary MCU?
Often the MCUs dedicated to controlling 3D printers have a limited and
pre-configured number of exposed pins to manage the main printing
functions (thermal resistors, extruders, steppers ...). Using the RPi
where Klipper is installed as a secondary MCU gives the possibility to
directly use the GPIOs and the buses (i2c, spi) of the RPi inside
klipper without using Octoprint plugins (if used) or external programs
giving the ability to control everything within the print GCODE.
**Warning**: If your platform is a _Beaglebone_ and you have correctly
followed the installation steps, the linux mcu is already installed
and configured for your system.
## Install the rc script
If you want to use the host as a secondary MCU the klipper_mcu process
must run before the klippy process.
After installing Klipper, install the script. run:
```
cd ~/klipper/
sudo cp ./scripts/klipper-mcu.service /etc/systemd/system/
sudo systemctl enable klipper-mcu.service
```
## Building the micro-controller code
To compile the Klipper micro-controller code, start by configuring it
for the "Linux process":
```
cd ~/klipper/
make menuconfig
```
In the menu, set "Microcontroller Architecture" to "Linux process,"
then save and exit.
To build and install the new micro-controller code, run:
```
sudo service klipper stop
make flash
sudo service klipper start
```
If klippy.log reports a "Permission denied" error when attempting to
connect to `/tmp/klipper_host_mcu` then you need to add your user to
the tty group. The following command will add the "pi" user to the
tty group:
```
sudo usermod -a -G tty pi
```
## Remaining configuration
Complete the installation by configuring Klipper secondary MCU
following the instructions in
[RaspberryPi sample config](../config/sample-raspberry-pi.cfg) and
[Multi MCU sample config](../config/sample-multi-mcu.cfg).
## Optional: Enabling SPI
Make sure the Linux SPI driver is enabled by running
`sudo raspi-config` and enabling SPI under the "Interfacing options"
menu.
## Optional: Enabling I2C
Make sure the Linux I2C driver is enabled by running `sudo raspi-config`
and enabling I2C under the "Interfacing options" menu.
If planning to use I2C for the MPU accelerometer, it is also required
to set the baud rate to 400000 by: adding/uncommenting
`dtparam=i2c_arm=on,i2c_arm_baudrate=400000` in `/boot/config.txt`
(or `/boot/firmware/config.txt` in some distros).
## Optional: Identify the correct gpiochip
On Raspberry Pi and on many clones the pins exposed on the GPIO belong
to the first gpiochip. They can therefore be used on klipper simply by
referring them with the name `gpio0..n`. However, there are cases in
which the exposed pins belong to gpiochips other than the first. For
example in the case of some OrangePi models or if a Port Expander is
used. In these cases it is useful to use the commands to access the
_Linux GPIO character device_ to verify the configuration.
To install the _Linux GPIO character device - binary_ on a debian
based distro like octopi run:
```
sudo apt-get install gpiod
```
To check available gpiochip run:
```
gpiodetect
```
To check the pin number and the pin availability tun:
```
gpioinfo
```
The chosen pin can thus be used within the configuration as
`gpiochip<n>/gpio<o>` where **n** is the chip number as seen by the
`gpiodetect` command and **o** is the line number seen by the`
gpioinfo` command.
***Warning:*** only gpio marked as `unused` can be used. It is not
possible for a _line_ to be used by multiple processes simultaneously.
For example on a RPi 3B+ where klipper use the GPIO20 for a switch:
```
$ gpiodetect
gpiochip0 [pinctrl-bcm2835] (54 lines)
gpiochip1 [raspberrypi-exp-gpio] (8 lines)
$ gpioinfo
gpiochip0 - 54 lines:
line 0: unnamed unused input active-high
line 1: unnamed unused input active-high
line 2: unnamed unused input active-high
line 3: unnamed unused input active-high
line 4: unnamed unused input active-high
line 5: unnamed unused input active-high
line 6: unnamed unused input active-high
line 7: unnamed unused input active-high
line 8: unnamed unused input active-high
line 9: unnamed unused input active-high
line 10: unnamed unused input active-high
line 11: unnamed unused input active-high
line 12: unnamed unused input active-high
line 13: unnamed unused input active-high
line 14: unnamed unused input active-high
line 15: unnamed unused input active-high
line 16: unnamed unused input active-high
line 17: unnamed unused input active-high
line 18: unnamed unused input active-high
line 19: unnamed unused input active-high
line 20: unnamed "klipper" output active-high [used]
line 21: unnamed unused input active-high
line 22: unnamed unused input active-high
line 23: unnamed unused input active-high
line 24: unnamed unused input active-high
line 25: unnamed unused input active-high
line 26: unnamed unused input active-high
line 27: unnamed unused input active-high
line 28: unnamed unused input active-high
line 29: unnamed "led0" output active-high [used]
line 30: unnamed unused input active-high
line 31: unnamed unused input active-high
line 32: unnamed unused input active-high
line 33: unnamed unused input active-high
line 34: unnamed unused input active-high
line 35: unnamed unused input active-high
line 36: unnamed unused input active-high
line 37: unnamed unused input active-high
line 38: unnamed unused input active-high
line 39: unnamed unused input active-high
line 40: unnamed unused input active-high
line 41: unnamed unused input active-high
line 42: unnamed unused input active-high
line 43: unnamed unused input active-high
line 44: unnamed unused input active-high
line 45: unnamed unused input active-high
line 46: unnamed unused input active-high
line 47: unnamed unused input active-high
line 48: unnamed unused input active-high
line 49: unnamed unused input active-high
line 50: unnamed unused input active-high
line 51: unnamed unused input active-high
line 52: unnamed unused input active-high
line 53: unnamed unused input active-high
gpiochip1 - 8 lines:
line 0: unnamed unused input active-high
line 1: unnamed unused input active-high
line 2: unnamed "led1" output active-low [used]
line 3: unnamed unused input active-high
line 4: unnamed unused input active-high
line 5: unnamed unused input active-high
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 |