Skip to content

Identifying the mcu on your host machine

This tutorial guides you through the steps of identifying the serial connection klipper needs to communicate with your mcu. It needs to be done for each mcu in your printer, e.g. for a display, input shaper, klipper expander, etc.

Note

Even though they might cover different featues, all MCUs look the same to klipper. A display has GPIO pins, so does the main mcu. Klippy can connect to multiple MCUs at once. A fully loaded Voron V0.2 might have a a main mcu, a V0 Display, an input shaper board and a klipper expander. With all of them connected, your printer.cfg must contain four [mcu] entries, each with its own serial property.

See also https://www.klipper3d.org/Installation.html#configuring-klipper

Power on the host and make sure all mcu‎s you want to use are connected and powered on. Connect to your host using SSH.

Listing all MCUs

klippy usually communicates with each mcu through a serial port, accessed via a tty device on the linux host it's running on. These devices show up in the /dev/ folder as /dev/ttyUSB0. These names are not stable and might change between reboots, which is why a more stable alias is needed.

The following script will list all plugged-in, initialized TTYs, among those hopefully all mcus.

Danger: Executing random scripts strangers give you

... is the best way to compromise your system. Whenever you see a curl -sSL ... | bash command on these sites, run it first without the | bash and inspect it.

Paste this into your terminal
curl -sSL https://reemo3dp.github.io/scripts/find_mcus.sh | bash
find_mcus.sh
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
#!/bin/bash

# Exit script immediately on error, uninitialized or if any piped command fails
set -euo pipefail

find_ttys() {
    # Taken from https://unix.stackexchange.com/a/144735
    # Enumerates all USB devices found in sysfs, finds the ones with a tty
    # and prints the device name, the serial number and
    # all associated links (e.g. in /dev/serial)
    for sysdevpath in $(find /sys/bus/usb/devices/usb*/ -name dev); do
        (
            set +u
            syspath="${sysdevpath%/dev}"
            devname="$(udevadm info -q name -p $syspath)"
            [[ "$devname" == "bus/"* ]] && exit
            eval "$(udevadm info -q property --export -p $syspath)"
            ! [[ "$SUBSYSTEM" == "tty" ]] && exit
            echo "$ID_SERIAL at $ID_PATH"
            echo "/dev/$devname"
            printf '%s\n' $DEVLINKS
            echo ""
        )
    done
}

# TTYs will always be at the root level, even if udev is broken
echo "###### Root Dev TTYs"
find /dev -maxdepth 1 \( -name 'ttyUSB*' -o -name 'ttyACM*' \) || true
echo ""

# Listing all `/dev/serial` symlinks helps identifying name collisions in `by-id`
echo "###### /dev/serial symlinks"
find /dev/serial -type l -exec file {} \; || true
echo ""

# Printing `lsusb` potentially shows MCUs in DFU/HID mode
echo "###### lsusb"
lsusb --tree
echo ""

# Finally, print all properly initialized TTYs
echo "###### All TTYs"
find_ttys

On a Voron V0.2 with a V0 Display mcu and a Mellow Fly Gemini V3, the output might look like this:

# Root Dev TTYs
/dev/ttyACM0
/dev/ttyACM1

# /dev/serial symlinks
/dev/serial/by-path/platform-1c1b400.usb-usb-0:1:1.0: symbolic link to ../../ttyACM1
/dev/serial/by-path/platform-1c1d400.usb-usb-0:1:1.0: symbolic link to ../../ttyACM0
/dev/serial/by-id/usb-Klipper_stm32f405xx_300028001751399999999999-if00: symbolic link to ../../ttyACM1
/dev/serial/by-id/usb-Klipper_stm32f042x6_2C0002001943311111111111-if00: symbolic link to ../../ttyACM0

# lsusb
/:  Bus 09.Port 1: Dev 1, Class=root_hub, Driver=ehci-platform/1p, 480M
/:  Bus 08.Port 1: Dev 1, Class=root_hub, Driver=ehci-platform/1p, 480M
    |__ Port 1: Dev 2, If 0, Class=Vendor Specific Class, Driver=mt7601u, 480M
/:  Bus 07.Port 1: Dev 1, Class=root_hub, Driver=ohci-platform/1p, 12M
    |__ Port 1: Dev 2, If 0, Class=Communications, Driver=cdc_acm, 12M
    |__ Port 1: Dev 2, If 1, Class=CDC Data, Driver=cdc_acm, 12M
/:  Bus 06.Port 1: Dev 1, Class=root_hub, Driver=ohci-platform/1p, 12M
/:  Bus 05.Port 1: Dev 1, Class=root_hub, Driver=ohci-platform/1p, 12M
    |__ Port 1: Dev 2, If 0, Class=Communications, Driver=cdc_acm, 12M
    |__ Port 1: Dev 2, If 1, Class=CDC Data, Driver=cdc_acm, 12M
/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=ohci-platform/1p, 12M
/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=ehci-platform/1p, 480M
    |__ Port 1: Dev 2, If 0, Class=Video, Driver=uvcvideo, 480M
    |__ Port 1: Dev 2, If 1, Class=Video, Driver=uvcvideo, 480M
    |__ Port 1: Dev 2, If 2, Class=Audio, Driver=snd-usb-audio, 480M
    |__ Port 1: Dev 2, If 3, Class=Audio, Driver=snd-usb-audio, 480M
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci-platform/1p, 480M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=musb-hdrc/1p, 480M

# All TTYs
Klipper_stm32f405xx_300028001751399999999999 at platform-1c1b400.usb-usb-0:1:1.0
/dev/ttyACM1
/dev/serial/by-path/platform-1c1b400.usb-usb-0:1:1.0
/dev/serial/by-id/usb-Klipper_stm32f405xx_300028001751399999999999-if00

Klipper_stm32f042x6_2C0002001943311111111111 at platform-1c1d400.usb-usb-0:1:1.0
/dev/ttyACM0
/dev/serial/by-id/usb-Klipper_stm32f042x6_2C0002001943311111111111-if00
/dev/serial/by-path/platform-1c1d400.usb-usb-0:1:1.0

Warning

You should be 100% certain about which serial belongs to which MCU. Mixing these up can damage your hardware! The most definitive way is to plug-in each MCU one after another and running the script from above to identify the new entry.

stm32f405xx, respectively stm32f042x6 identifies the model of the stm32 microcontroller on each mcu. If this is enough to identify your mcu (e.g. stm32f042 is usually the V0Display), then you can put the by-id-symlinks for each mcu in its respective config section in your printer.cfg:

[mcu]
serial: /dev/serial/by-id/usb-Klipper_stm32f405xx_300028001751399999999999-if00

[mcu display]
serial: /dev/serial/by-id/usb-Klipper_stm32f042x6_2C0002001943311111111111-if00

Troubleshooting

The folder /dev/serial/ doesn't exist or is empty

Update your system. systemd 247 and/or 252 have wrong udev rules that prevent proper initialization of these symlinks.