Also release owned Pins with Usart::free()

[timokroeger]

Return ownership of the pins back to the user when calling free()
Useful to multiplex a single USARTE instance to multiple serial connections on different pins (for smaller NRF52 devices which only have one USARTE instance).

Alternative: Only take a reference to the pins in in new().
Please let me know which one is the preferred approach.

[jonas-schievink]

Alternative: Only take a reference to the pins in in new().

This would mean that Usart<_>: 'static never holds and prevent usage of Usart in RTIC resources, so we probably shouldn't do that.

I think we can do better than storing the Pins instance in every Usart though – what if we just read from the USART's pin configuration registers in free and create the pins from those? That way we don't have to pay for the extra Pins storage.

[timokroeger]

Reading back the pins from the peripheral is a nifty idea. Going to try that tomorrow.

[Yatekii]

Cool stuff, thanks for doing this! I required this a few times already but just for debugging things and I just used unsfe for that :P

I think we can do better than storing the Pins instance in every Usart though – what if we just read from the USART's pin configuration registers in free and create the pins from those? That way we don't have to pay for the extra Pins storage.

I fully agree with this :)

[jonas-schievink]

Cool! Can you also add a changelog entry?