Multiple Identical Serial Devices & Soultion for MCU Connection Issues

[xboxhacker]

I recently got a bdwidth for my Klipper TronXY Veho600 printer. I instantly ran into issues with MCU connection problems. After spending 2 full days working it out, it is now working fine. I want to put this here in case someone else is having the same MCU connection problems I had.

Hardware:

• TronXY stm32f446
• BTT Pi 1.2
• bdwidth

It would seem my main board uses the same CH340 as the bdwidth. This caused a conflict when connecting to the MCU. Vendor 1a86, same product, no unique serial.

Result: using /dev/serial/by-id/usb-1a86_USB_Serial-if00-port0 is ambiguous and will sometimes point to the MCU, other times to the sensor, causing read errors.

NOTE: I 100% do not know what I am doing, but I dug and dug to work this solution out. There may be far better ways to do this, but it works for me.

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1. Identify Your Devices

Plug in both USB-serial devices (e.g., printer board and filament sensor).

List all USB serial devices:

ls -l /dev/ttyUSB*
ls -l /dev/serial/by-path

Unplug one device to see which /dev/ttyUSB* disappears—this helps you match each device to its function.

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2. Get Each Device's Physical USB Path

For each device, run:

udevadm info -q property -n /dev/ttyUSB0 | grep ^ID_PATH=
udevadm info -q property -n /dev/ttyUSB1 | grep ^ID_PATH=

Example output:

ID_PATH=platform-5101400.usb-usb-0:1:1.0
ID_PATH=platform-5200400.usb-usb-0:1:1.0

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3. Create a udev Rules File

Create /etc/udev/rules.d/99-serial-stable-names.rules with your favorite editor.

sudo nano /etc/udev/rules.d/99-serial-stable-names.rules

Paste this into Nano:

# Replace ID_PATH values with those from your system!
SUBSYSTEM=="tty", ENV{ID_PATH}=="<YOUR PATH HERE>", SYMLINK+="mcu"
SUBSYSTEM=="tty", ENV{ID_PATH}=="<YOUR PATH HERE>", SYMLINK+="bdwidth"

Save the new file with CTRL + X

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4. Reload udev and Replug Devices

sudo udevadm control --reload-rules
sudo udevadm trigger -s tty

Check the new symlinks:

ls -l /dev/mcu /dev/bdwidth

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5. Update Your Klipper printer.cfg

[mcu]
serial: /dev/mcu
restart_method: command

[bdwidth]
port: usb
serial: /dev/bdwidth
extruder: extruder
enable: all
<rest of the config from the git>

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6. Troubleshooting

• If /dev/mcu or /dev/bdwidth don’t appear, double-check the ID_PATH values and your rules file for typos.
• Reload rules and replug both devices.
• Use sudo udevadm test $(udevadm info -q path -n /dev/ttyUSB0) to debug rule application.
• Never move the device to a different USB port, or you’ll need to redo the steps above.

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Bonus: Use by-path Directly (Quick Hack)

You can also use /dev/serial/by-path/... in your config if you don't want to set up custom names.

Example:

[mcu]
serial: /dev/serial/by-path/platform-5101400.usb-usb-0:1:1.0
restart_method: command

Untested by me...

[markniu]

This is very useful. Thanks for sharing!