Last year,in mid 2023, I updated my Ender 5 plus by changing the controller board to a BTT Manta E3EZ with a CM4 module.

Some days ago I updated the Pi compute module (both Debian release and rpi-update), and since then, the serial connection to the micro-controller unit (aka MCU) is not working anymore. I’ve re-installed a fresh version of the system using the last octopi image but this didn’t fixed the issue.

On the CM4, the serial port is correctly detected:

pi@octopi:~ $ ls -l /dev/serial/by-id/*
lrwxrwxrwx 1 root root 13 May 18 12:23 /dev/serial/by-id/usb-Klipper_stm32g0b1xx_4A001B000C504B5735313920-if00 -> ../../ttyACM0

But when I test to connect to it wth minicom, if fails to use 250000 baud rate (falling back to 115200) and displays garbage.

pi@octopi:~ $ minicom -o -b 250000 -D /dev/ttyACM0

How can I fix this ?

The kernel version is: 6.1 but the version 6.6 was also not working

Linux version 6.1.21-v7l+ (dom@buildbot) (arm-linux-gnueabihf-gcc-8 (Ubuntu/Linaro 8.4.0-3ubuntu1) 8.4.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #1642 SMP Mon Apr  3 17:22:30 BST 2023

The serial port is in fact an USB device and is correctly detected by the Linux kernel

[    7.232515] cdc_acm 1-1.1:1.0: ttyACM0: USB ACM device
[    7.234675] usbcore: registered new interface driver cdc_acm
[    7.234693] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters

And the details of the USB device:

Bus 001 Device 003: ID 1d50:614e OpenMoko, Inc. stm32g0b1xx
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            2 Communications
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        16
  idVendor           0x1d50 OpenMoko, Inc.
  idProduct          0x614e 
  bcdDevice            1.00
  iManufacturer           1 Klipper
  iProduct                2 stm32g0b1xx
  iSerial                 3 4A001B000C504B5735313920
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x003e
    bNumInterfaces          2
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0xc0
      Self Powered
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         2 Communications
      bInterfaceSubClass      2 Abstract (modem)
      bInterfaceProtocol      1 AT-commands (v.25ter)
      iInterface              0 
      CDC Header:
        bcdCDC               1.10
      CDC ACM:
        bmCapabilities       0x06
          sends break
          line coding and serial state
      CDC Union:
        bMasterInterface        0
        bSlaveInterface         1 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0008  1x 8 bytes
        bInterval             255
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass        10 CDC Data
      bInterfaceSubClass      0 
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0

Thanks.