Error when setting UART Baudrate <= 2400 on a STM32H5

[DrTom]

I get an ValueError: set baudrate 2500 is not within 5% of desired value whenever I try to set a baudrate to 2400 or lower and it seems that the lowest value the UART port will assume is actually 2500.

The board is the following: https://github.com/WeActStudio/WeActStudio.STM32H5_64Pin_CoreBoard and the board configuration is here: https://github.com/DrTom/micropython-wrap/tree/main/boards/STM32H562RG_WAS.

Is there something wrong with the my configuration or is there a Problem with micropython UARTs on the H5?

I have seen there were similar issues in the past. Some of them were related to the LPUART controller. The latter seems not to be the case here: the board has 1 LPUART but I can reproduce the problem when using UART2 or UART3.

[DrTom]

It seems that CPU and bus frequency might be not set correctly:

>>> import machine
>>> machine.freq()
(160000000, 160000000, 160000000, 160000000)

The first value could/should be 250'000'000 and not 160'000'000. More over:

I am not sure if this applies here but on the pyboard pyb.freq() the two latter values return the bus speed which is related to the UART baud settings.

https://docs.micropython.org/en/latest/library/pyb.UART.html#methods
| The minimum baudrate is dictated by the frequency of the bus that the UART is on;

[DrTom]

The problem ist most likely related to the bus frequency. After increasing the CPU speed and unintentionally with it the bus speed (see DrTom/micropython-wrap@08b2fc1) the not within 5% of desired value arises now at even higher baud settings.

So the question is now: how do I configure the bus speed properly. It seems that

>>> machine.freq()
(200000000, 200000000, 200000000, 200000000)

should rather be (200000000, 200000000, 42000000, 84000000) or even better (250000000, 250000000, 42000000, 84000000)?