Linux MCU¶

Your single-board computer (SBC) 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 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: An LED strip controlled via GPIO20

[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 I2C 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: