Notes on putting micropython on STM32F407VG bare board
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README.md

STM32F407VG & Micropython

Notes on putting micropython on STM32F407VG $10 bare board

A pyboard on steroids? Well, it has more GPIO pins, anyway.

For the moment, a quick look at the following site may be of help in understanding this board: https://github.com/BLavery/STM32F407VG-Arduino and especially on how to set boot jumper and reset into dfu (bootloader) mode.

The DIY board MCU is '407VG. This is the same MCU as on the STM32 F4 Discovery board, which already has a micropython firmware build.

We can load that micropython binary on our DIY board. Here is what I did:

  • In boot mode (reset with jumper on boot1),
  • using linux (debian mint),
  • which has dfu-util available,
  • with merely a USB connection,
  • using the standard latest firmware image (STM32F4 Discovery) from here: http://micropython.org/download

... we can put the micropython image on this board (bootloader mode, jumper on boot1, press reset):

sudo dfu-util -a 0 -D STM32F4DISC-20181207-v1.9.4-725-gd690c2e14.dfu      (our dfu file)

THAT'S SO EASY.

Linux has dfu-util easily available. If you run Windows, this guide should help to do the DFU upload:
http://micropython.org/resources/Micro-Python-Windows-setup.pdf

Swap the boot jumper from boot1 to boot0 and press reset to re-enable run mode.

Here we have a slight glitch. The "real" F4 DISC board has a voltage sensor on PA9 to detect that the USB is plugged in. Our DIY board doesn't have that, but the code we installed thinks we have a real F4 DISC, and USB won't start. We can fudge a HIGH voltage on PA9 if we can get a fix into file main.py on the python. But we can't get at that file until the USB starts.

Solution: temporarily connect a jumper wire from +3V to PA9. Reset. On your computer, a new "drive" appears on the filemanager, "PYBFLASH", with empty boot.py and main.py already present. Use any editor to add these 2 lines to main.py:

from machine import Pin
Pin("PA9", Pin.OUT).high()

This will hold PA9 high. Save. Unmount/eject/remove the PYBFLASH drive. (Get used to doing this!) Remove the temporary jumper. Reset. The PYBFLASH drive should return, without needing the jumper wire. Glitch finished. Remember not to use PA9 for other things (eg UART1) in future.

USB now gives us a serial connection as well. Run a serial terminal utility. (I use gtkterm). On linux my port name is /dev/ttyACM0 or similar. I'm sure you Win or Mac folk can work out your equivalent. Baudrate seens to be self-sensing, I think.

A crtl-C and ctrl-D get you in and out of the REPL (interpreter) prompt of micropython.

KeyboardInterrupt: 
MicroPython v1.9.4-725; F4DISC with STM32F407VG
Type "help()" for more information.
>>> 

PYB: sync filesystems
PYB: soft reboot

Our DIY board has a LED on PE0. Use any editor to upgrade main.py to this:

from time import sleep
from machine import Pin
Pin("PA9", Pin.OUT).high()
led=Pin("PE0", Pin.OUT)
while 1:
  led.value(1-led.value())
  sleep(1)

Save file. Unmount flash. Reset board. Lo, the led blinks.

A new world beckons.

http://docs.micropython.org (.. and follow the pyboard specifics, not esp8266 or wipy. Because pyboard also uses STM32F407!)


So we now have the STM32F4 Discovery board micropython running on our DIY board. There are a few hardware differences (read: things NOT fitted on our DIY board) that would be good to have some firmware adjustments for:

  • No sensing of "USB plugged in" voltage (We had a workaround above)
  • Not 4 LEDs, just one, on a different pin. Active low, not high.
  • The USR button on different pin. Active low, not high.
  • The pins for UART1 no longer conflicted by the "USB plugged in" sensing
  • No SD flash slot fitted to board

It's not too difficult to recompile the micropython firmware to exactly match our DIY board. I did it on my linux PC, set up as per the file compile-micropython.doc. I added the STM32F407 folder from here into my .../micropython/ports/stm32/boards/ folder, alongside the other board variants. The new variant board is just a clone of STM32F4DISC, with config tweaks to only 2 files.

Positioning my terminal into .../micropython/ports/stm32 folder:

    make STM32F407

In a few minutes I have fresh new firmware called "firmware.dfu" in a newly-created folder .../micropython/ports/stm32/build-STM32F407. To upload, change directory to that, and, as before, change boot jumper, reset to bootloader, and

   sudo dfu-util -a 0 -D firmware.dfu

It should work cleanly. The USB starts automatically now, without the PA9 glitch-fixer above. Even the Safe Mode and Flash Volume Reset work. (We get single/double/triple LED flashes, not 3 colours.) See http://docs.micropython.org/en/latest/pyboard/tutorial/reset.html

And you shouldn't need to recompile. I have put a compiled firmware here for your download. Still faithfully just called firmware.dfu.


The flash volume that stores boot.py, main.py and you own project files is about 92K (112K less overheads). It could be a limitation if your project grows. If you are willing to be recompiling your own firmware.dfu file, which I just suggested you shouldn't need to do, then you can save some space. You can "freeze" some of your library files into the firmware image, which does have plenty of spare room. But search elsewhere on just how to do that.

Otherwise, I also tried with SPI connections to add an SD card and an external 2MB flash chip, using the drivers micropython offers here: .../micropython/drivers. Both attempts failed, and after googling around, I suspect this area (adding external FAT volumes) is broken in micropython and has been for a while. So make do with the internal 92K filespace you have.