Linux RPi MCU¶

Your single-board computer (SBC), such as a Raspberry Pi, can be used as a secondary MCU in Klipper. This allows you to use the GPIOs and buses (I2C, SPI) of your SBC directly in your Klipper configuration. For example to control additional fans, LEDs, or to read sensors without needing extra hardware.

Install the Systemd Service¶

The klipper-mcu service must start before Klipper itself. To install and enable it, run:

cd ~/klipper/
sudo cp ./scripts/klipper-mcu.service /etc/systemd/system/
sudo systemctl enable klipper-mcu.service

Build the Micro-Controller Code¶

Start by configuring the firmware for the Linux process. Run:

cd ~/klipper/
make clean
make menuconfig

In the menu, set Microcontroller Architecture to Linux process, then press Q to exit and press Y to save the configuration.

Flash the Micro-Controller¶

To build and install the firmware, run:

sudo systemctl stop klipper.service
make flash
sudo systemctl start klipper.service

Permission Denied Error

If klippy.log reports a "Permission denied" error when connecting to /tmp/klipper_host_mcu, add your user to the tty group:

sudo usermod -a -G tty $USER

Configure the MCU in printer.cfg¶

Add the following section to your printer.cfg to enable your SBC as a secondary MCU:

[mcu host]
serial: /tmp/klipper_host_mcu

After saving, restart Klipper. You can now reference the host MCU pins in your configuration using the host: prefix, for example:

Example 1: A led strip controlled by the GPIO20 on the RPi

[output_pin caselight]
pin: host:gpio20
# You can also write the pin in extended form by specifying
# the reference gpiochip.
#pin: host:gpiochip0/gpio20

Example 2: Using the i2c bus of the RPi to read a sensor

[temperature_sensor enclosure_temp]
sensor_type: HTU21D
i2c_mcu: host
i2c_bus: i2c.1
htu21d_hold_master: False

Further Information¶

For more details and optional features like enabling SPI, I2C, identifying the correct gpiochip, or using hardware PWM, refer to the official Klipper documentation: