A USI software UART for the ATtiny 25/45/85
Revised and edited to compile with avr-gcc for the ATtiny45 from https://bitbucket.org/tinusaur/usiuartx The original was based on reference to "AVR307" Half Duplex UART Using the USI Module on tinyAVR and megaAVR devices - application note. This version is configured for 2400 baud at a system clock of 1mhz. The code should be easily adapted to any avr device with USI.