# MCU unable to connect/suddenly no serial connection possible **URL:** \ **Category:** General Discussion\ **Created:** [April 21, 2024, 5:36am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923 "2024-04-21T05:36:50Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 21, 2024, 5:36am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/1 "2024-04-21T05:36:51Z")
### Basic Information: Printer Model: Qidi X Max 3 Vanilla Klipper 0.12 MCU / Printerboard: MKSPI Host / SBC klippy.log ### Hello, my system stopped working after I fiddled around with USB plugs conecting a webcam. Everything worked great for a long time. I also ran the updates for all the components this morning. Klippy.log says that mcu is unable to open serial port: Could not configure port. I dont understand. Why this error. Everything is connected and shows up in the commandline. The config didn’t change in any way… Ideas much appreciated! Thank you! ![image](https://global.discourse-cdn.com/free1/uploads/klipper/original/2X/3/324ddcfa9850de6e6e41dd7573e4604821e2b24b.png) ![image](https://global.discourse-cdn.com/free1/uploads/klipper/original/2X/d/d545a539f4ac1e94ed9d2ceb6712b29a8817deec.png) … [klippy.log](https://klipper.discourse.group/uploads/short-url/iBea4ERuE3BY3mryfGgKcYwm0qX.log) (7.0 MB) ---
**Author:** ![EddyMI3D](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/eddymi3d/32/1981_2.png) [@EddyMI3D](https://klipper.discourse.group/u/EddyMI3D)\ **Post date:** [April 21, 2024, 6:28am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/2 "2024-04-21T06:28:04Z")
Klipper does not complain ```auto [mcu MKS_THR] serial = /dev/serial/by-id/usb-Klipper_rp2040_A5D94D9519ED5658-if00 ``` It complains ```auto [mcu] serial = /dev/ttyS0 restart_method = command ``` ```auto mcu 'mcu': Starting serial connect mcu 'mcu': Unable to open serial port: Could not configure port: (5, 'Input/output error') ``` The issue does not appear at the start of the log. Isn’t the mcu not connected? * * * BTW: Can’t understand why people install KAMP on Klipper 0.12.0 ---
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 21, 2024, 6:36am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/3 "2024-04-21T06:36:45Z")
> [@EddyMI3D](#): > > The issue does not appear at the start of the log. Isn’t the mcu not connected? I don’t understand what you ask. Do you mean if the cable is unplugged or something? Sorry about KAMP 🙂 Actually I use only the smart park feature and the line purge from it… ---
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 21, 2024, 6:40am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/4 "2024-04-21T06:40:16Z")
Edit: All was running fine until I plugged an USB hub to the board. An attempt to utilize more usb ports for camera and such… After this it didn’t recognize the cam as before and it didn’t work at all with this hub. So I unplugged it and set everything back as before. I hope I didn’t kill the board or something…. ---
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 21, 2024, 4:00pm UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/5 "2024-04-21T16:00:32Z")
Anybody has an idea how to further narrow down error in mcu communication? ---
**Author:** ![EddyMI3D](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/eddymi3d/32/1981_2.png) [@EddyMI3D](https://klipper.discourse.group/u/EddyMI3D)\ **Post date:** [April 21, 2024, 4:10pm UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/6 "2024-04-21T16:10:55Z")
So, when you remove the USB hub and connect the MCU directly to the host, does that work again? USB hubs can be quite painful when used with 3D printers. ---
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 21, 2024, 4:29pm UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/7 "2024-04-21T16:29:36Z")
Yes I bet. > So, when you remove the USB hub and connect the MCU directly to the host, does that work again? No, no of course I removed the device and it’s back to normal now. But it doesn’t work. I get the mcu communication error after 1 minute where Klipper is reporting „start up“…… ---
**Author:** ![EddyMI3D](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/eddymi3d/32/1981_2.png) [@EddyMI3D](https://klipper.discourse.group/u/EddyMI3D)\ **Post date:** [April 21, 2024, 6:48pm UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/8 "2024-04-21T18:48:00Z")
Can please provide a recent klippy.log ---
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 22, 2024, 5:58am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/9 "2024-04-22T05:58:24Z")
[klippy (1).log](https://klipper.discourse.group/uploads/short-url/coZQKGZZOFImhriEOcebgH1rHLi.log) (588.5 KB) ---
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 22, 2024, 6:03am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/10 "2024-04-22T06:03:43Z")
I can add a more specific question. The mainboard MCU is not connecting via serial and I don’t know why. In the config you have this: ![image](https://global.discourse-cdn.com/free1/uploads/klipper/original/2X/a/a583fe5fe6948651e83e44e749c225cf32504dca.png) When I type: sudo lsof | grep /dev/tty I see the following: ![image](https://global.discourse-cdn.com/free1/uploads/klipper/original/2X/1/1b4881d07ca9024ffe7c47b461f56f9ab225ac0b.png) I tried to use other dev/tty… options available. No luck. Any other low level diagnostic approach ? Btw: I just re-flashed the board with a freshly compiled binary. No luck either. ---
**Author:** ![EddyMI3D](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/eddymi3d/32/1981_2.png) [@EddyMI3D](https://klipper.discourse.group/u/EddyMI3D)\ **Post date:** [April 22, 2024, 6:07am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/11 "2024-04-22T06:07:23Z")
I found this: > **[GitHub - makerbase-mks/MKS-PI: As we all know, the Klipper firmware has the...](https://github.com/makerbase-mks/MKS-PI?tab=readme-ov-file#connection-mks-pi-with-motherboard)** > > As we all know, the Klipper firmware has the advantages of high printing speed, high precision, and the ability to use the web page to control the printer, etc. MKS PI is a high-end microcomputer b... So ```auto [mcu] serial = /dev/ttyS0 ``` is meant to connect via UART. ---
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 22, 2024, 6:39am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/12 "2024-04-22T06:39:03Z")
Yes you are correct. It’s connected via UART. ---
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 22, 2024, 7:08am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/13 "2024-04-22T07:08:24Z")
> [@EddyMI3D](#): > > is meant to connect via UART. What is your comment about? ---
**Author:** ![EddyMI3D](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/eddymi3d/32/1981_2.png) [@EddyMI3D](https://klipper.discourse.group/u/EddyMI3D)\ **Post date:** [April 22, 2024, 7:55am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/14 "2024-04-22T07:55:53Z")
It’s a verification that you connect via UART ---
**Author:** ![remarkable\_sir](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@remarkable\_sir](https://klipper.discourse.group/u/remarkable_sir)\ **Post date:** [April 25, 2024, 3:28am UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/15 "2024-04-25T03:28:13Z")
My problem is not a Klipper topic but apparently rather an armbian problem. I had to re image the system and set up the same configuration. Problem gone. Obviously putting stuff into your USB port can be quite exciting. In my case the UART connection that ties in the mainboard MCU via /dev/ttyS0 vanished and all efforts to bring it back online where unsuccesful. Be careful! ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/klipper/original/1X/64419bf2aac6639e6ef5cef200dcd456b0a01ac3.png) [@system](https://klipper.discourse.group/u/system)\ **Post date:** [May 25, 2024, 1:29pm UTC](https://klipper.discourse.group/t/mcu-unable-to-connect-suddenly-no-serial-connection-possible/15923/16 "2024-05-25T13:29:10Z")
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