dupterm/mpremote not working correctly over uart?

[RotatingLlama]

Hello,

I'm trying to shift my REPL to a UART port for development, because the USB port on the board will be inaccessible once the project is fully built up. I've got the UART pins brought out to a USB COM port adapter for now, and I can talk to it just fine using PuTTY - I get the REPL, I can run commands as I'd expect, no problems.

But development environments don't work with it.

Thonny gives me:

Device is busy or does not respond. Your options:

  - wait until it completes current work;
  - use Ctrl+C to interrupt current work;
  - reset the device and try again;
  - check connection properties;
  - make sure the device has suitable MicroPython / CircuitPython / firmware;
  - make sure the device is not in bootloader mode.

Micropico (VS Code) has 2025-06-02 19:36:47.910 [error] [PicoRemoteFileSystem] stat: unexpected result type for / in its log.

mpremote tells me this:

Connected to MicroPython at COM5
Use Ctrl-] or Ctrl-x to exit this shell

...but ignores all input other than Ctrl-x and Ctrl-] (typing isn't even locally echoed)

I have no main.py, but the following in boot.py, which apparently is sufficient to get the REPL in PuTTY at least:

from machine import UART, Pin
from os import dupterm

# Set up the UART
uart = UART(0)
uart.init( baudrate=9600, bits=8, parity=None, stop=1, tx=Pin(0), rx=Pin(1) )

# Send the REPL to the UART
dupterm(uart)
print('boot.py')

My guess is there's a simple thing that I'm doing wrong, but I can't for the life of me figure out what it is. Thonny and mpremote are definitely using the correct COM port, although micropico doesn't tell you which one it's trying to use so I can't verify that. I'm running MicroPython 1.24 on a RPi Pico.
Any help, please?

[Josverl]

The default only baudrate that is supported by mpremote and most other tools is 115200
so I'd suggest changing to uart.init( baudrate=115200, ....

[RotatingLlama]

there's a simple thing that I'm doing wrong

That was the thing! Thankyou 😊