# Mcu 'rpi' unable to connect

**URL:** <https://klipper.discourse.group/t/mcu-rpi-unable-to-connect/25336>\
**Category:** General Discussion\
**Created:** [December 10, 2025, 8:22pm UTC](https://klipper.discourse.group/t/mcu-rpi-unable-to-connect/25336 "2025-12-10T20:22:18Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![AddamLupus](https://avatars.discourse-cdn.com/v4/letter/a/71e660/32.png) [@AddamLupus](https://klipper.discourse.group/u/AddamLupus)\
**Post date:** [December 10, 2025, 8:22pm UTC](https://klipper.discourse.group/t/mcu-rpi-unable-to-connect/25336/1 "2025-12-10T20:22:18Z")

</div>

### Basic Information:

Printer Model:Neptune 4 Pro with OpenNeptune

[klippy.log](https://klipper.discourse.group/uploads/short-url/t8j2dsa0J1I1kKjKpmxOJh1gCLz.log) (1.2 MB)

MCU / Printerboard:  
 Host / SBC  
 klippy.log

_Fill out above information and_ _ **in all cases attach your** _ **`klippy.log` _file_** (use zip to compress it, if too big). _Pasting your_ `printer.cfg` _is **not** needed_  
_ **Be sure to check our “Knowledge Base” Category first. Most relevant items, e.g. error messages, are covered there** _

### Describe your issue:

Hey guys.2 days ago i shutdown my printer properly and today when i turned it on it felt weird then the “mcu ‘rpi’: Unable to connect” error code popped up.Everything is up to date and i dont know what to do

…

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<div class="post-metadata">

**Author:** ![cardoc](https://avatars.discourse-cdn.com/v4/letter/c/ec9cab/32.png) [@cardoc](https://klipper.discourse.group/u/cardoc)\
**Post date:** [December 10, 2025, 8:47pm UTC](https://klipper.discourse.group/t/mcu-rpi-unable-to-connect/25336/2 "2025-12-10T20:47:33Z")

</div>

This file

```auto
[mcu rpi]
serial = /tmp/klipper_host_mcu

```

is likely missing or corrupted. Details at the link below.

> **[RPi microcontroller - Klipper documentation](https://www.klipper3d.org/RPi_microcontroller.html?h=rpi#rpi-microcontroller)**
>
> This document describes the process of running Klipper on a RPi and use the same RPi as secondary mcu.

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<div class="post-metadata">

**Author:** ![AddamLupus](https://avatars.discourse-cdn.com/v4/letter/a/71e660/32.png) [@AddamLupus](https://klipper.discourse.group/u/AddamLupus)\
**Post date:** [December 10, 2025, 8:50pm UTC](https://klipper.discourse.group/t/mcu-rpi-unable-to-connect/25336/3 "2025-12-10T20:50:32Z")

</div>

I didnt touch any mcu config yet.Its worked until 2 days ago.

My code looks like this:

```auto
[mcu rpi] 

serial: /tmp/klipper_host_mcu

[adxl345]

cs_pin: rpi:None

spi_bus: spidev0.2

```

I dont know what happened with it

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<div class="post-metadata">

**Author:** ![cardoc](https://avatars.discourse-cdn.com/v4/letter/c/ec9cab/32.png) [@cardoc](https://klipper.discourse.group/u/cardoc)\
**Post date:** [December 10, 2025, 9:35pm UTC](https://klipper.discourse.group/t/mcu-rpi-unable-to-connect/25336/4 "2025-12-10T21:35:16Z")

</div>

On a RPi the first suspect is the SD card. They do wear out.

In anu case Klipper has to read that file to enable the [mcu rpi]. You could comment out the lines and all the accelerometer references. Klipper should be happy but obviously the accelerometer will no longer work.

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<div class="post-metadata">

**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/klipper/original/1X/64419bf2aac6639e6ef5cef200dcd456b0a01ac3.png) [@system](https://klipper.discourse.group/u/system)\
**Post date:** [February 8, 2026, 9:35pm UTC](https://klipper.discourse.group/t/mcu-rpi-unable-to-connect/25336/5 "2026-02-08T21:35:59Z")

</div>

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