stm32/usart: Changing baud rate

[EnmanuelParache]

As discussed in #1289 adding support to changing the baud rate for stm32 usart.

[Dirbaio]

could you not duplicate this chunk of code? for example making configure() call here.

[EnmanuelParache]

Sure I can, but my only concern is that calling configure would require the developer to pass the Config struct again to avoid overwriting any previous configuration made on Usart instance construction when perhaps all it wants is just to change the baudrate all this since Config is not copied in Usart instance to reuse its values.

I noticed I can reduce code duplication by moving static DIVS to the outer scope, and wrap Usart kind matching and brr search in two separate functions to be used by both configure and set_usart_baudrate if you think this would be better.

[Dirbaio]

configure does more things, so I meant make configure() call set_usart_baudrate() then do the other stuff.

[EnmanuelParache]

Ah, sorry I misunderstood you. But yeah that makes total sense. I just pushed changes addressing this. Calling find_and_set_brr in both configure and set_baud_rate reducing code duplication. Please take a look and let me know what you think.

[MabezDev]

Where does this stop if we accept this change, will there be an set/get for every item in the config? On top of that, you then have to forward many of those methods to the sub structs UartTx, UartRx, RingBufferedRx etc etc.

Imo adding multiple ways to do things can get a bit messy. I saw in the original issue the concern was not overwriting the current config I think there are two better ways to solve this:

• Store the current config in the driver itself
  • Depending on the driver, this can be costly in memory footprint, some analysis might need to be done here
  • At least in the case of UART, the config is quite cheap
• Add a current_config() which reads back and constructs the config
  • This might not be possible for all registers? or costly (CPU time) to reverse the calculation to get back to the source values

There is also a third:

• Make the user in charge of storing the config and only changing what they need to (AKA reject this PR and document this)

Just some opinion of a user, feel free to ignore :)

[MabezDev]

These impls should also be extended to Buffered* and RingBuffered* structs

[EnmanuelParache]

Thanks for the feedback, just did that. Please take a look

[vongaisberg]

This change is required to generate a DMX signal. Changing the baudrate using set_config is too slow, the pins go into floaing for ~100µs.