.. _module-pw_sys_io_baremetal_stm32f429:

-----------------------------
pw_sys_io_baremetal_stm32f429
-----------------------------
``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.

Setup
=====
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.

.. 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
   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
-------------------------

.. code-block:: text

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

Dependencies
============
- :ref:`module-pw_sys_io`
- :ref:`module-pw_preprocessor`