Clarify documentation of UART

[uzytkownik]

I'm trying to use sercom::v2 but it hangs during enabling of SERCOM due to SYNCBUSY being high. I suspect that I did not configured clocks correctly as it just specify to configure them in documentation.

It would be nice if documentation/examples was improved to show how the clocks should be configured.

[bradleyharden]

@uzytkownik, could you give a little more detail? Are you using a particular board, or the HAL directly? Are you on master? Which chip are you using? Which SYNCBUSY bit is high?

Many of the BSP examples show how to configure the clocks. Have you seen those? We could probably document the clock module better, but there's also a new version on the way in #450.

[uzytkownik]

@bradleyharden Sure. I just figured out what is wrong and posted as issue #528. However the story is:

• metro_m4 0.9.0 function uart asks for Port. It is unclear how to get it and the structure is marked as deprecated.
• metro_m4 0.9.0 examples uses sercom::v1 directly. Better but the v1 is deprecated and throws warnings (TBH I haven't tried it)
• metro_m4 master example uses new uart function - not applicable to 0.9.0
• metro_m4 uart implementation used sercom0 (issue metro_m4 HAL configures incorrect clock in metro_m4::uart #528 ) which didn't worked either. But I didn't know that so I tried to use code directly.

[bradleyharden]

@uzytkownik, it sounds like #528 is the real problem. Can we close this issue?