.. _weact_stm32g431_core:

WeAct Studio STM32G431 Core Board
#################################

The WeAct STM32G431 Core Board is a low-cost bare-bones STM32G431-based development
board. See the `STM32G431CB website`_ for more information about the MCU. More information
about the board, including schematics, is available from the `WeAct GitHub`_.

Modifications USB-C Power Delivery
**********************************

The board does not support USB-C PD in its standard configuration. To enable USB-C PD, CC1
and CC2 need to be disconnected from their pull-down resistors and be connected to PB6 and
PB4 respectively. Dead battery support requires PA9 and PA10 to be routed to CC1 and
CC2. VBUS also needs to be connected to the MCU through a voltage divider.

The pull-downs are disconnected by removing the zero-Ohm resistors on SB8 and SB9 next to
the USB-C connector. SB3, SB5, SB6, and SB7 then need to be closed to connect the CCx
lines to the MCU. The voltage divider is connected to PB2 by closing SB4.

After these modifications have been made, PA9, PA10, PB2, PB4, and PB6 should be
considered reserved for USB-C and not available for other applications.

.. warning::
   The internal USB DFU boot loader may not work correctly with machines that respect USB
   PD signaling unless dead battery support has been enabled. A USB-C to USB-A adapter or
   programming using the SWD port can be used as a workaround.


Supported Features
==================

The Zephyr weact_stm32g431_core board configuration supports the following hardware
features:

+------------+------------+-------------------------------------+
| Interface  | Controller | Driver/Component                    |
+============+============+=====================================+
| NVIC       | on-chip    | nested vector interrupt controller  |
+------------+------------+-------------------------------------+
| UART       | on-chip    | serial port                         |
+------------+------------+-------------------------------------+
| GPIO       | on-chip    | gpio                                |
+------------+------------+-------------------------------------+
| ADC        | on-chip    | ADC Controller                      |
+------------+------------+-------------------------------------+
| USB        | on-chip    | USB device                          |
+------------+------------+-------------------------------------+
| UCPD       | on-chip    | ucpd                                |
+------------+------------+-------------------------------------+

The default configuration can be found in the defconfig file:

        ``boards/arm/weact_stm32g431_core/weact_stm32g431_core_defconfig``

Pin Mapping
===========

Default Zephyr Peripheral Mapping:
----------------------------------

- UART_2 TX/RX   : PA2/PA3
- UCPD1 CCx      : PB6/PB4 (not connected by default)
- UCPD1 DBCCx    : PA9/PA10 (not connected by default)
- BUTTON (User)  : PC13
- BUTTON (BOOT0) : PB8
- LED0           : PC6
- ADC (VBUS)     : PB2

The ADC is disabled by default since the VBUS voltage divider is not connected in the
board's standard configuration.


Hardware Configuration
----------------------
+---------------+---------+-----------------------------------------------+
| Solder bridge | Default | Description                                   |
+===============+=========+===============================================+
| SB1/SB2       | Open    | Route PC14/PC15 (LSE) to header               |
+---------------+---------+-----------------------------------------------+
| SB6/SB7       | Open    | Connect PB4/PB6 (UCPD1_CCx) to USB-C CCx pins |
+---------------+---------+-----------------------------------------------+
| SB3/SB5       | Open    | Connect PA9/PA10 (UCPD1_DBCCx) to to PB6/PB4  |
+---------------+---------+-----------------------------------------------+
| SB4           | Open    | Connect PB2 to VBUS voltage divider           |
+---------------+---------+-----------------------------------------------+
| SB8/SB9       | Closed  | Connect USB-CCx to pull-down resistors        |
+---------------+---------+-----------------------------------------------+
| SB10          | Open    | VBUS protection diode bypass                  |
+---------------+---------+-----------------------------------------------+


Clock Sources
-------------

The board has two external oscillators. The frequency of the slow clock (LSE) is 32.768
kHz. The frequency of the main clock (HSE) is 8 MHz.

The default configuration sources the system clock from the PLL, which is derived from
HSE, and is set at 144 MHz. The 48 MHz clock used by the USB interface is derived from the
PLL instead of the internal 48 MHz oscillator.

Programming and Debugging
*************************

The MCU is normally programmed using the ROM bootloader or the exposed SWD port.

Please note that some laptops may not detect the ROM bootloader correctly if the CCx
pull-downs have been disconnected by opening SB8 and SB9 unless dead battery support has
been enabled by closing SB3 and SB5. A USB-C to USB-A adapter can be used as a workaround
if this is a problem.

Flashing an Application
=======================

Connect a USB-C cable and the board should power ON. Force the board into DFU mode by
keeping the BOOT0 switch pressed while pressing and releasing the NRST switch.

The dfu-util runner is supported on this board and so a sample can be built and tested
easily.

.. zephyr-app-commands::
   :zephyr-app: samples/basic/blinky
   :board: weact_stm32g431_core
   :goals: build flash

Debugging
=========

The board can be debugged by installing the included 100 mil (0.1 inch) header, and
attaching an SWD debugger to the 3V3 (3.3V), GND, SCK, and DIO pins on that header.


References
**********

.. target-notes::

.. _WeAct GitHub:
   https://github.com/WeActStudio/WeActStudio.STM32G431CoreBoard

.. _STM32G431CB website:
   https://www.st.com/en/microcontrollers-microprocessors/stm32g431cb.html

.. _STM32F401x reference manual:
   https://www.st.com/resource/en/reference_manual/rm0440-stm32g4-series-advanced-armbased-32bit-mcus-stmicroelectronics.pdf