Port, board and/or hardware

Host Windows (any hardware)

MicroPython version

• mpremote 1.27.0

Reproduction

1. On Windows, have a MicroPython device with a file containing Unicode text:

   /unicode_test/नेपाली_नाम.txt
   

2. Run mpremote cat interactively in PowerShell (NOT piped or captured):

   mpremote cat :/unicode_test/नेपाली_नाम.txt
   

3. The command hangs indefinitely. Even with PYTHONIOENCODING=utf-8 set, it still hangs.

4. Press Ctrl-C to interrupt.

Observations

The same command works correctly when:

• Output is piped: mpremote cat :file.txt > output.txt
• Output is captured by subprocess: subprocess.run([...], capture_output=True)
• Running on Linux (even in WSL2 on the same machine)

The hang ONLY occurs when stdout is a real Windows console (isatty=True).

Expected behaviour

$ mpremote cat :/unicode_test/नेपाली_नाम.txt

Nepali Name - नेपाली नाम

This file tests Nepali (Devanagari) script.

Script: Devanagari (Nepali variant)

Vowels: अ आ इ ई उ ऊ ऋ ए ऐ ओ औ
Consonants: क ख ग घ ङ च छ ज झ ञ ट ठ ड ढ ण त थ द ध न
...

for test files see : [https://github.com/[Josverl/unicode_mpy](https://github.com/Josverl/unicode_mpy)

https://github.com/Josverl/unicode_mpy/tree/main/test_data/South_Asian_Indic


### Observed behaviour

The command hangs indefinitely when run interactively on Windows with Unicode content. Ctrl-C shows the following traceback:

Traceback (most recent call last):
File "...\mpremote\main.py", line 614, in main
handler_func(state, args)
File "...\mpremote\commands.py", line 421, in do_filesystem
state.transport.fs_printfile(path)
File "...\mpremote\transport.py", line 129, in fs_printfile
self.exec(cmd, data_consumer=stdout_write_bytes)
File "...\mpremote\transport_serial.py", line 309, in exec
ret, ret_err = self.exec_raw(command, data_consumer=data_consumer)
File "...\mpremote\transport_serial.py", line 296, in exec_raw
return self.follow(timeout, data_consumer)
File "...\mpremote\transport_serial.py", line 204, in follow
data = self.read_until(1, b"\x04", timeout=timeout, data_consumer=data_consumer)
File "...\mpremote\transport_serial.py", line 146, in read_until
data_consumer(new_data)
File "...\mpremote\transport.py", line 36, in stdout_write_bytes
sys.stdout.buffer.flush()
KeyboardInterrupt

### Additional Information


**Initial hypothesis (DISPROVEN):** The hang was suspected to be in `stdout_write_bytes()`:
```python
def stdout_write_bytes(b):
    sys.stdout.buffer.write(b)
    sys.stdout.buffer.flush()  # <-- Suspected to hang

Test result: A standalone Python script calling sys.stdout.buffer.write() + flush() with identical Unicode content does NOT hang.

Actual cause: The hang is NOT in CPython's stdout handling. The issue is elsewhere in mpremote, possibly:

• Different code path when stdout.isatty() is True vs False
• Threading/synchronization issues between reader/writer threads
• Windows console API interaction issues
• Serial/socket transport blocking behavior

Possibly Related Issues

• https://github.com/micropython/micropython/issues/15228 - Unable to print unicode characters when running repl with mpremote

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