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.. _chapter-pw-sys-io-baremetal-stm32f429:
.. default-domain:: cpp
.. highlight:: sh
``pw_sys_io_baremetal_stm32f429`` implements the ``pw_sys_io`` facade over
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
3. Build an executable with a main() function using a toolchain that
supports Cortex-M4.
.. note::
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
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
.. code-block:: text
--USB Serial--+ +-----STM32F429 MCU-----
| |
TX o--->o PA10/USART1_RX
| |
RX o<---o PA9/USART1_TX
| |
--------------+ +-----------------------
* ``pw_sys_io`` facade
* ``pw_preprocessor`` module