* Add standalone UART example
* Add UART example to docs in UART module
* Add core::fmt::write_str to UART module to allow easy use of format! macro in user code
* Improve clock frequency stuff for uninitialized clocks
- Made clocks singletons so the frequency handling actually works as expected
- Added initial frequencies
- Improved the docs
- Added a Clock trait
* Add pico examples.
These have the benefit of knowing which external crystal is attached.
Even though it always should be a 12 MHz crystal.
Thus we can setup the clocks properly
I also changed the rp2040 examples to work out of the box for pico boards since that will probably be used most of the time
* PWM functionality
* Updated prelude.rs
* Added example, cleaned up the PWM HAL.
* Renamed a file for clarity
* Changes to address C-CTOR recommendations, only 8 PWM channels, restructuring
* Forgot to remove a test function, and added a quick comment.
* Cleaned up code now that PWM channels are clustered in the PAC.
Bring in line with atsamd-hal GPIO v2
Copied as much as possible. Docs lifted mostly as-is.
Also add sample BSP for the Feather RP2040 in boards/feather_rp2040
May include a few random fixes from currently futile attempt to get doctests working.
Sorry this is a large commit :(
This adds support for input pins, including pulling them high or low.
It also adds two examples: the start of a classic blinky LED example, and an example for reading input.
