## Serial Interface

Instead of polling for input we use an interrupt vector
to write data to a rx ring buffer when it's available.

We parse commands using a state machine so we can deal
with small chunks of characters at a time and spit out
the parsed command when the transmission has finished.

TODO: System clock frequency should be a multiple of
1.8432MHz for perfect USART. This means we would need
an external crystal oscillator.

TODO: Do we need to handle backspaces for interactive
serial consoles?! Overkill?!

### Supported Commands

Optional decimal point for numbers.

- START
- RESET
- STOP
- SET TEMP 20.0
- SET DEWP 60.0