# Internal error in MCU 'mcu' stepcompress and lost connection with MMB

**URL:** <https://klipper.discourse.group/t/internal-error-in-mcu-mcu-stepcompress-and-lost-connection-with-mmb/20251>\
**Category:** General Discussion\
**Created:** [November 25, 2024, 12:08pm UTC](https://klipper.discourse.group/t/internal-error-in-mcu-mcu-stepcompress-and-lost-connection-with-mmb/20251 "2024-11-25T12:08:29Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![dinamicby](https://avatars.discourse-cdn.com/v4/letter/d/3d9bf3/32.png) [@dinamicby](https://klipper.discourse.group/u/dinamicby)\
**Post date:** [November 25, 2024, 12:08pm UTC](https://klipper.discourse.group/t/internal-error-in-mcu-mcu-stepcompress-and-lost-connection-with-mmb/20251/1 "2024-11-25T12:08:29Z")

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### Basic Information:

- **Printer Model:** Custom
- **MCU / Printerboard:** BTT M8P V2.0
- **Host / SBC:** CB1
- **Printhead:** EBB36 CAN V1.1,
- **klippy.log:**  
[logs.zip](https://klipper.discourse.group/uploads/short-url/rWy9loE4CS3xEKfPEKHcpW8pjPd.zip) (6.2 MB)  
also use BTT MMB
- **Klipper version:** v0.12.0-378

### Issue:

During an SD card print of a large model (400x400x400 mm build area), the printer encountered a loss of communication with the MCU, causing the print to stop. The error was triggered by internal failures in processing the `G1` command, specifically related to the `stepcompress` module on the microcontroller. Despite multiple troubleshooting attempts, the issue persists in occurs in random time.  
Voltage stability has been thoroughly checked, and no irregularities were found.  
The issue persists even after increasing the CAN bus buffer size.

Main errors that i found:

- `Lost communication with MCU 'MMB'`.
- `mcu.error: Internal error in MCU 'mcu' stepcompress`.
- Failure during `G1` command processing

## Please need an assistance 😩

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<div class="post-metadata">

**Author:** ![Sineos](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/sineos/32/18_2.png) [@Sineos](https://klipper.discourse.group/u/Sineos)\
**Post date:** [November 25, 2024, 12:18pm UTC](https://klipper.discourse.group/t/internal-error-in-mcu-mcu-stepcompress-and-lost-connection-with-mmb/20251/2 "2024-11-25T12:18:30Z")

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The original error is

```auto
Timeout with MCU 'MMB' (eventtime=8629.364980)
Transition to shutdown state: Lost communication with MCU 'MMB'

```

See [Timeout with MCU / Lost communication with MCU](https://klipper.discourse.group/t/timeout-with-mcu-lost-communication-with-mcu/6639)  
The rest seem to be consequential errors that are likely unrelated to the root cause.

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<div class="post-metadata">

**Author:** ![dinamicby](https://avatars.discourse-cdn.com/v4/letter/d/3d9bf3/32.png) [@dinamicby](https://klipper.discourse.group/u/dinamicby)\
**Post date:** [November 25, 2024, 12:20pm UTC](https://klipper.discourse.group/t/internal-error-in-mcu-mcu-stepcompress-and-lost-connection-with-mmb/20251/3 "2024-11-25T12:20:54Z")

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Could the issue potentially be related to CAN bus overload or its unstable operation?  
We’ve double-checked all the wiring and voltage, everything is stable. The printer can run for up to 6 hours without issues, but then this error occurs.

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<div class="post-metadata">

**Author:** ![Sineos](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/sineos/32/18_2.png) [@Sineos](https://klipper.discourse.group/u/Sineos)\
**Post date:** [November 25, 2024, 12:26pm UTC](https://klipper.discourse.group/t/internal-error-in-mcu-mcu-stepcompress-and-lost-connection-with-mmb/20251/4 "2024-11-25T12:26:01Z")

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The common reasons are listed in the above article. It is equally applicable to USB / CAN or any other communication ways.  
For dedicated CAN troubleshooting also see [CANBUS Troubleshooting - Klipper documentation](https://www.klipper3d.org/CANBUS_Troubleshooting.html)

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<div class="post-metadata">

**Author:** ![dinamicby](https://avatars.discourse-cdn.com/v4/letter/d/3d9bf3/32.png) [@dinamicby](https://klipper.discourse.group/u/dinamicby)\
**Post date:** [November 25, 2024, 12:28pm UTC](https://klipper.discourse.group/t/internal-error-in-mcu-mcu-stepcompress-and-lost-connection-with-mmb/20251/5 "2024-11-25T12:28:06Z")

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Thank you so much

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**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/klipper/original/1X/64419bf2aac6639e6ef5cef200dcd456b0a01ac3.png) [@system](https://klipper.discourse.group/u/system)\
**Post date:** [January 24, 2025, 12:28pm UTC](https://klipper.discourse.group/t/internal-error-in-mcu-mcu-stepcompress-and-lost-connection-with-mmb/20251/6 "2025-01-24T12:28:47Z")

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