ESP32-C3 UART init error

[shariltumin]

Has anyone had the same experience when working with the UART on the ESP32-C3?

MPY: soft reboot
MicroPython v1.27.0-preview.160.g8757eb715e on 2025-09-20; ESP32C3 module with ESP32C3
Type "help()" for more information.
>>> from machine import UART, Pin
>>> u1 = UART(1)
E (38893) uart: uart_wait_tx_done(1444): uart driver error
>>> u1
UART(1, baudrate=115211, bits=8, parity=None, stop=1, tx=10, rx=9, rts=-1, cts=-1, txbuf=256, rxbuf=256, timeout=0, timeout_char=0, irq=0)
>>> u1.write(b'xxxxx yyyyyy zzzzz')
18
>>> u1.any()
18
>>> w = u1.read()
>>> w
b'xxxxx yyyyyy zzzzz'
>>> import platform
>>> platform.platform()
'MicroPython-1.27.0-preview-riscv-IDFv5.4.2-with-newlib4.3.0'

I got a "uart driver error," but the UART seems to be functioning normally. Can someone explain why this happened?

[robert-hh]

That's not limited to the C3, and an error message that is definitely new.
But it seems easy to fix..

[shariltumin]

Yes, disabling uart_wait_tx_done() in the mp_machine_uart_init_helper() function seem to fix the issue.

$ diff machine_uart.c-KAKI5 machine_uart.c
257c257
<     // uart_wait_tx_done(self->uart_num, pdMS_TO_TICKS(1000)); !!!  try disable this
---
>     uart_wait_tx_done(self->uart_num, pdMS_TO_TICKS(1000));

[robert-hh]

I made a PR as a fix.