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Documentation/stm32h5: board.h clock defines.

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Document the board.h keep-HSI-running-in-stop-mode define
STM32_BOARD_HSIKERON_ENABLE and the USART clock source
selection defines.

Signed-off-by: Liam Howatt <liamhowatt@geotab.com>
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Liam Howatt 2026-09-18 16:12:24 -04:00 • committed by Alan C. Assis
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Documentation/platforms/arm/stm32h5/index.rst
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@ -135,6 +135,26 @@ of the block size and count when partitioning the OTP area for their needs.
``len`` is the number of bytes - not words. It has no alignment requirement. ``offset`` is
the offset in bytes. It must be a multiple of 4.
Clocks
------
``STM32_BOARD_HSIKERON_ENABLE`` can be defined in board.h to keep HSI running in
STOP mode. This can be used to keep a peripheral clocked by HSI running in
STOP mode.
``STM32_RCC_CCIPR1_U[S]ARTxSEL`` (e.g. ``STM32_RCC_CCIPR1_USART3SEL``) can be defined as one of
- ``RCC_CCIPR1_U[S]ARTxSEL_RCCPCLK1``
- ``RCC_CCIPR1_U[S]ARTxSEL_PLL2QCK``
- ``RCC_CCIPR1_U[S]ARTxSEL_PLL3QCK``
- ``RCC_CCIPR1_U[S]ARTxSEL_HSIKERCK``
- ``RCC_CCIPR1_U[S]ARTxSEL_CSIKERCK``
- ``RCC_CCIPR1_U[S]ARTxSEL_LSECK``
E.g. ``RCC_CCIPR1_USART3SEL_HSIKERCK`` in board.h to select the clock source for that USART.
The clock source is set in RCC initialization. Only stm32_serial.c is aware of this setting.
TODO: Make stm32_lowputc.c aware of this clock source setting too.
References
=================
[RM0481] Reference Manual: STM32H523/33xx, STM32H562/63xx, and STM32H573xx Arm® -based 32-bit MCUs