G4TGJ AVR Radio Library
This library is a set of source files for AVR processors that provide functionality of use in amateur radio applications, although many of the files could also be used in non-radio systems.
They provide CAT control, display, EEPROM, I2C, LCD, millisecond timer, morse keyer, oscillator (si5351a), pushbutton, rotary control and serial support.
They should work on most 8-bit AVR processors including the ATmega, ATtiny and tinyAVR 1-series.
See TARL documentation for how to use the library.