MCU Protocol error

From time to time it happens that there are changes in the Klipper communication between host and MCU. That make it necessary to update all your MCUs to fix the communication error.

Description of the error message

Screenshot of the "MCU Protocol error" message

In the middle of the error message, all MCUs are listed with their current version. In my case, you can see the Klipper version on the host is v0.12.0-75-gc6136bfd.

Directly below the current Klipper version is a list of all MCUs that still need to be updated. In my case, these are:

  • mcu: Current version v0.11.0-225-g38e79dff

  • EBBCan: Current version v0.12.0-61-gb50d6669

  • display: Current version v0.11.0-225-g38e79dff

It is also common to have a "Linux MCU". This is mostly used when using an accelerometer (ADXL345, LIS2DW, MPU-6000/9000 series) directly via the GPIO of the Raspberry Pi. This MCU is usually called rpi.

After the outdated MCUs follows a list of all the MCUs that have already been updated to the latest version. There isn't a single one yet, so it says <none> here.

How to compile a new firmware

You must compile a new firmware to flash it onto the MCU. For this, you need the Klipper firmware settings for the board. These settings can be found in the example file from Klipper:

To open the Klipper firmware config tool, connect to your printer via SSH and execute the following commands:

cd ~/klipper
make menuconfig

After you have set all the settings, you can close the menu (press the key q). To clear the cache and build the new firmware, execute these commands:

make clean

The firmware is now compiled and ready for flashing. The file is in ~/klipper/out/klipper.bin.

Flash the firmware onto the board

The compiled firmware must now be flashed onto the board. There are several ways to do this. Unfortunately, there is no generally valid solution. Most standard boards can be flashed with the following method. At first we have to read the serial by-id path of the MCU:

ls /dev/serial/by-id/*

The output should look like this:


With this serial path, you can execute the flash command:

sudo systemctl stop klipper
make flash FLASH_DEVICE=<serial path to the board>
sudo systemctl start klipper

If this command does not work for your board, other options exist. First, you can reread the example configuration to see if your board has another description to flash the board.

There are also these options:

  • Klipper SD-Card Updates If a board has already been flashed with Klipper and has a sd card slot, the firmware can be transferred to the sd card in the slot via the board connection and flashed.

  • Katapult Katapult is an alternative bootloader for printer boards. This bootloader is very popular with CAN Toolhead boards. The current board connection can also be used to flash the firmware to the MCU.

Need help

If, despite these instructions, you still have problems flashing your board or cannot find a config for your board/MCU, please get in touch with your Klipper/Printer Discord/Forum or ask here on the Mainsail communication channels:

Getting Help

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