pbarada opened a new pull request, #21400:
URL: https://github.com/apache/nuttx/pull/21400
Fixup RCC code for STM32H7S3L8 boards (stm32h7s8-dk and nucleo-h7s3l8):
- DIVR fields are not documented in RM0477 (they are reserved)
- Reserved bits in RCC registers must be kept at reset value
- Compile-time compute derived frequencies from sources
- Only set PLL DIV[P,Q,S,T] fields (and enable dividers) if defined
- Compile-time compute PLL[1-3]RGE fields from PLL refx_ck
- Provide macros to convert from prescalers to CPRE, BMPRE, PPRE fields
- Compile-time validate PLL divisors and bus clock prescalers
## Summary
Cleanup STM32H7RS RCC code to derive register field values for
divisors/prescalers from their values and compute frequencies for the various
clocks from sources and divisor/prescalers. Clock setup for stm32h7rs now only
requires:
- defining PLL source
- define clock source frequencies
- define PLL source
- define DIVM/DIVN as well as (optionally) define DIVP, DIVQ, DIVS, DIVT
divisors for each PLL
- define CPRE and BMPRE cpu and bus prescalers
Frequencies for all RCC clocks are computed at compile time from above
information.
## Impact
User experience: No adaptation required. This fix should make it easier to
configure clocks for stm32h7rs boards.
Build: No impact.
Hardware: Affects stm32h7s3l8 based-boards (nucleo-h7s3l8 and stm32h7s8-dk).
Documentation: No impact.
Security: No impact.
Compatibility: Backward compatible
## Testing
Build Host:
- OS: Ubuntu 24.04.4 LTS
- Compiler: arm-none-eabi-gcc 13.2.1
Target:
- Architecture: ARM (STM32H7S3L8)
- Board: STM32H7S8-DK and NUCLEO_H7S3L8
- Configuration: Default jumbo-xip and boot-xip for both boards
- Ran ostest to successful completion
Build/booted each configuration (both with HSI and HSE as PLL), ran ostest
to completion.
From stm32h7s8-dk console:
```
Bootloader 13.1.0 95305908f8-dirty Nov 2 2026 19:36:30 arm stm32h7s8-dk
telnetd [6:100]
NuttShell (NSH) NuttX-13.1.0
nsh> uname -a
NuttX 13.1.0 95305908f8-dirty Nov 2 2026 19:36:36 arm stm32h7s8-dk
nsh>
```
From nucleo-h7s3l8 console:
```
NuttShell (NSH) NuttX-13.1.0
nsh> uname -a
NuttX 13.1.0 95305908f8-dirty Nov 2 2026 19:36:50 arm nucleo-h7s3l8
nsh>
```
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