Klipper USB-to-CAN bus bridge

Klipper has also the posibillity to use the U2C as a USB-to-CAN bus bridge. This is a good solution if you want to use the board as a CANBUS adapter for your printer and an MCU at the same time.
In the case of the BigTreeTech U2C, this solution has no advantages over the candlelight firmware, since no freely usable pins are available on the board.

This guide is tested with the following boards:

• BigTreeTech U2C v2.1

This guide was verified on a Pi running MainsailOS

Configure Klipper firmware

Open the config interface of the Klipper firmware with following commands:

cd ~/klipper
make menuconfig

and set the following settings:

• Enable extra low-level configuration options: check
• Micro-controller Architecture: STMicroelectronics STM32
• Processor model: STM32G0B1
• Bootloader offset: No bootloader (without CanBoot)
• Bootloader offset: 8KiB bootloader (with CanBoot)
• Clock Reference: 8 MHz crystal
• Communication interface: USB to CAN bus bridge (USB on PA11/PA12)
• CAN bus interface: CAN bus (on PB5/PB6)
• CAN bus speed: 500000

The result should look like this:

Klipper config for U2C v2.x in bridge mode

use q for exit and y for save these settings.

Now clear the cache and compile the Klipper firmware:

make clean
make

Flash Klipper

There are two ways to flash the Klipper firmware to the board.

• Flash the firmware via USB (without CanBoot)
• Flash the firmware via USB (with CanBoot)

Flash Klipper via USB without CanBoot

This is the classic way to flash the firmware to the board.

First, you have to put the board into DFU mode. To do this, press and hold the boot button and then disconnect and reconnect the power supply. With the command dfu-util -l, you can check if the board is in DFU mode.

It should then look like this:

If your board is in DFU mode, you can flash Klipper with the following command:

dfu-util -a 0 -D ~/klipper/out/klipper.bin -s 0x08000000:mass-erase:force:leave

Flash Klipper via USB with CanBoot

This method is necessary if you don't have Klipper on your board, but flashed the CanBoot firmware already.

At first, you have to get the serial ID for your board. To do this, you have to exectute the following command:

# find your <serial device> full path
ls /dev/serial/by-id/*

Then you have to use this path in the following command:

# flash Klipper
python3 ~/CanBoot/scripts/flash_can.py -f ~/klipper/out/klipper.bin -d <serial device>

This should look like this:

Power cycle the board and you are done.

Add can0 interface

Now you only have to create the interface in the OS. to do this, create the file /etc/network/interfaces.d/can0 and fill it with the following content.

# open file with nano
sudo nano /etc/network/interfaces.d/can0

/etc/network/interfaces.d/can0

allow-hotplug can0
iface can0 can static
    bitrate 500000
    up ifconfig $IFACE txqueuelen 128

To save and close the nano editor:
ctrl+s => save file
ctrl+x => close editor

After a reboot, the can interface should be ready.

Add the MCU in Klipper (optional)

Finally, you can add the board to your Klipper printer.cfg with its UUID:

printer.cfg

[mcu U2C]
canbus_uuid: <uuid>

# embedded temperature sensor
[temperature_sensor U2C]
sensor_type: temperature_mcu
sensor_mcu: U2C
min_temp: 0
max_temp: 100

If you don't know the UUID of your U2C, you can read it out with the following command:

~/klippy-env/bin/python ~/klipper/scripts/canbus_query.py can0

The output should look like this: