pw_sys_io_baremetal_stm32f429 implements the pw_sys_io facade over UART.

The STM32F429 baremetal sys IO backend provides device startup code and a UART driver layer that allows applications built against the pw_sys_io interface to run on a STM32F429 chip and do simple input/output via UART. The code is optimized for the STM32F429I-DISC1, using USART1 (which is connected to the virtual COM port on the embedded ST-LINKv2 chip). However, this should work with all STM32F429 variations (and even some STM32F4xx chips).

This backend has no configuration options. The point of it is to provide bare- minimum platform code needed to do UART reads/writes.


This module requires relatively minimal setup:

  1. Write code against the pw_sys_io facade.

  2. Specify the dir_pw_sys_io_backend GN global variable to point to this backend.

  3. Build an executable with a main() function using a toolchain that supports Cortex-M4.


This module provides early firmware init and a linker script, so it will conflict with other modules that do any early device init or provide a linker script.

Module usage

After building an executable that utilizes this backend, flash the produced .elf binary to the development board. Then, using a serial communication terminal like minicom/screen (Linux/Mac) or TeraTerm (Windows), connect to the device at a baud rate of 115200 (8N1). If you’re not using a STM32F429I-DISC1 development board, manually connect a USB-to-serial TTL adapter to pins PA9 (MCU TX) and PA10 (MCU RX), making sure to match logic levels (e.g. 3.3V versus 1.8V).

Sample connection diagram

--USB Serial--+    +-----STM32F429 MCU-----
              |    |
           TX o--->o PA10/USART1_RX
              |    |
           RX o<---o PA9/USART1_TX
              |    |
--------------+    +-----------------------


  • pw_sys_io facade

  • pw_preprocessor module