Start with Micropython on STM32

Micropython is a greate framework for fast prototyping embedded systems. Easy to use and userfrendly framewrok is completly free to us (commercial use to). Micropython is a C implementation Python3 for embedded. This Python Language Interpreter maby not super fast but very usefull. Not all Python 3 features have been implemented so far, but enough to write fully functional and usable code.

Frimware with Micropython is avilable on official project site. Full support help your resolve your problems.

Hardware preparation

This article describe how to launch Python code on STM32 Cortex-M microcontroller. We need NUCLEO-F401RE base board with microcontroller STM32F401RE to achieve this goal. We use build-on-platform ST-Link programmer to flash our STM32F401RE. Dor communication with main microcontroller we use UART2 avilable on pins PA2 (TX) and PA3 (RX).

STM32 Nucleo-F4101RE

However default UART2 on NUCLEO-F401RE is disabled. So we must enable this feature. We must use Solder Bridge on bottom side of the board. Solder Bridge number SB63 and SB62 are respectively TX and RX pins. This is Arduino Pinout standard.

Reconnect Solder Bridge number SB14 and SB13. Move resistor 0R into  SB63 and SB62 on bottom side of our Nucleo-F401RE board.

Nucleo Enable UART2

Be sure is your ST-Link is connecte with our target microcontroller STM32F401RE. For this purpose, connect the connectors on CN2 header. Now you can plug-in USB cable in your Computer.

Eanble ST-Link

Upload Firmware

Before upload Firmware with Micropython you can update ST-Link Firmware on Nucleo board but this step is not obligated.

Download and install on your computerr STM32 ST-LINK Utility software. Run application and choose ST-LINK -> Firmware Update.

Firmware ST-LINK update

In new window ST-LINK Upgrade click on button Device Connect and Yes. Be sure is your Board is connected to computer via USB interface. After a few moments, we will receive information about the success of the operation.

Update Firmware Successfull

Now we can upload new Firmware with Micropython into our tagert microcontroler STM32F401RE. Download newest stable verion of firmware from official website here is a link. Download latest DFU image with Firmware for NUCLEO_F401RE board. In our case: NUCLEO_F401RE-20200902-v1.13.dfu

For flash memory in our main microcontroller we use STM32 ST-LINK Utility Software (The same application as for the update ST-Link Firmware). Befor load new firmware into this application we must conwert DFU file into HEX file or S19 file. This is necessary because the current version of STM32 ST-LINK Utility (v4.5.0.0) doesn’t support files with extension *.dfu. So we use other software to convert DFU to acceptable file format.

Download and install DfuSe USB Software. Run sub-appliaction DFU File Manager and choose option: I want to EXTRACT S19, HEX or BIN files from a DFU one.

DfuSe USB

In new window DFU File Manager (v3.0.6) – Extract select appriopriate image and Extraction option  Hex.

Convert DFU into HEX

Now we are ready to load HEX file to STM32 ST-LINK Utility Application. Choose File -> Open file…

New Hex

Make sure the board is connected to computer and choose Program & Verify… In new windows click Start to run flash process.

Flash memory

Disconnect Nucleo board with Computer and press RESET Button on board. Micropython. Micropython was installed on our microcontroller!

First application

For communcation with Python Environment on STM32 microcontroller we use UART2. Use UART<->USB Adapter to connect STM32F401RE to Computer. Pin PA2 (TX) on Nucleo board connect to Pin RX UART-USB Adapter. Pin PA3 (RX) on Nucleo connect to Pin TX UART-USB Adapter.

Nucleo UART

Create example Python code and save to file with extension *.py. You can use your favourite Code Editor. Documentation and Code Snippet you can find on official Micropython website. Below is simple micropython code for Blinking User LED LS2 (Pin PA5) on Nucleo Board

from machine import Pin
from utime import sleep_ms

user_led = Pin('PA5', Pin.OUT)

while True:
    user_led.on()
    sleep_ms(1000)
    user_led.off()
    sleep_ms(1000)

For upload main.py file to microcontroller memory use rshell tool. Git repository is avilable here – rshell git repository. Another ability to access memory and save our main.py file with example code is use uPyCraft Tool. We recommend the use of rshell because it can sometimes have problems with uploading large files.

VSCode Rshell

After installed rshell use system terminall and three simple command to copy main.py file into system memory on embedded device. Command rshell run shell. Command connect serial COM6 115200 connecting our device via Serial on Port COM6 with boudrate 115.2k. Command cp main.py /flash/ copy source file main.py to destination location /flash/ memory.

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