Drop `#include "irq.h"` in `cpu.h`, which was there for a legacy work around.
A bunch of missing includes of `irq.h` materialized due to this and were
fixed.
For atmega boards a TX has not actually completed until UDRn is empty
as well as the Transmit Shift Register.
To avoid resetting an UART before a TX has completed we use the TXCn
flash and ISR to set a variables that indicates TX is ongoing. This
allows not reseting the UART while there are ongoing TX pending.
This fixes an issue where part of the last byte is not shifted out
of the TX shift register causing rubish on the first TX following an
uart_init.
Names with two leading underscores are reserved in any context of the c
standard, and thus must not be used. This ATmega platform used it however for
defining internal stuff. This commit fixes this.
The brr calculation on the datasheet is different than what is implmented.
This is intentional since it provides better rounding due to truncation.
There was no comment explaining that so this comment should prevent confusion.
* Add support for U2X switch to double transmission speed
* Provides lower error rates when needed
* Add support for static baud rate calculation, reduces computation by 10x
* adds support for statically enabling double speed baud
