Software DFU mode implementation for STM32F4 MCU.

[flom84]

Hello all

I have tried to add support for entering DFU mode from software as explained in the following issue: ##3444

The implementation particularly supports STM32F4 family since I have only one MCU from ST :)

The code follows the recommended steps from the application notes: AN2606 Rev 55. Link here: https://www.st.com/resource/en/application_note/cd00167594-stm32-microcontroller-system-memory-boot-mode-stmicroelectronics.pdf

To test, add the lines bellow in your code.py, run the program, then connect to the device with an ##utility as explained here: https://learn.adafruit.com/adafruit-stm32f405-feather-express/dfu-bootloader-details.

import microcontroller

microcontroller.on_next_reset(microcontroller.RunMode.BOOTLOADER)

microcontroller.reset()

[jepler]

This looks simple enough. I assume it works -- can you say specifically what device you tested it on?

[flom84]

@jepler I have tested on my NUCLEO-F446RE board: https://www.st.com/en/evaluation-tools/nucleo-f446re.html.
I have added circuitpython support for it on my local branch: d40278f , then used software DFU to do firmware upgrades.

[jepler]

Thank you! Low chance of negative impact, looks sensible to me, and you tested.

I hope you'll be submitting a PR to add that board soon, too.