I have various projects using AVR processors (ATTiny and ATMega) so there is a lot of similarity between the various source files. Rather than keep multiple copies of the same code I have created TARL - the TGJ AVR Radio Library. This 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), rotary control and serial support.

See TARL documentation for how to use the library.