Port, board and/or hardware

OPTA RS485

MicroPython version

Device: Arduino Opta RS485

MicroPython version: v1.26.1 (2025-09-11)

Flashed file: ARDUINO_OPTA-20250911-v1.26.1.dfu

Tools used: Thonny and mpremote

Installation method:Dfu-utils and Arduino’s official MicroPython installer (same result)

Reproduction

• Reset the Opta’s memory using the example sketch QSPIFormat from the Arduino IDE.

• Flash the latest .dfu file:

ARDUINO_OPTA-20250911-v1.26.1.dfu

• Disconnect and connect Usb cable
• Connect using Thonny or mpremote.

Every time I connect, I immediately see this error:

Traceback (most recent call last):
File "boot.py", line 3
SyntaxError: invalid syntax
MicroPython v1.26.1 on 2025-09-11; Arduino OPTA with STM32H747
Type "help()" for more information.

Expected behaviour

No response

Observed behaviour

I noticed that boot.py and main.py are always corrupted or encoded incorrectly after flashing.
Example of what boot.py looks like:

boot.py -- run on boot to configure USB and filesystem

Put app code in main®xù

ŠÂ^MŠéíøïúü¨íéëè...

I tried manually reformatting the flash memory:

import os, vfs, pyb
vfs.umount('/flash')
vfs.VfsFat.mkfs(pyb.Flash(start=0))
vfs.mount(pyb.Flash(start=0), '/flash')
os.chdir('/flash')

Then recreated a simple boot.py:

simple boot

print("BOOT OK")

After reset, this works fine:

BOOT OK
MicroPython v1.26.1 on 2025-09-11; Arduino OPTA with STM32H747

But when I upload a new main.py (even a simple one):

import time
print("start program")

for i in range(1, 100):
print(f"N Message: {i}")
time.sleep(1)

print("End program")

…the file becomes corrupted and unreadable:

import time
print("start pzográm"©ŠŠëïýîüíú¨½¨...

Then after reset:

BOOT OK
Traceback (most recent call last):
File "main.py", line 2
SyntaxError: invalid syntax

Additional Information

• The issue seems to be related to filesystem encoding or corruption after writing .py files.

• It happens both with Thonny and mpremote.

• I’ve confirmed the .dfu flash completes successfully each time.

Code of Conduct

Yes, I agree