core with up to 128K program memory
                   avr35 - classic AVR core with up to 64K program memory
                           plus the MOVW instruction
                   avr4  - enhanced AVR core with up to 8K program memory
                   avr5  - enhanced AVR core with up to 64K program memory
                   avr51 - enhanced AVR core with up to 128K program memory
                   avr6  - enhanced AVR core with up to 256K program memory
                   avrxmega2 - XMEGA, > 8K, < 64K FLASH, < 64K RAM
                   avrxmega3 - XMEGA, RAM + FLASH < 64K, Flash visible in RAM
                   avrxmega4 - XMEGA, > 64K, <= 128K FLASH, <= 64K RAM
                   avrxmega5 - XMEGA, > 64K, <= 128K FLASH, > 64K RAM
                   avrxmega6 - XMEGA, > 128K, <= 256K FLASH, <= 64K RAM
                   avrxmega7 - XMEGA, > 128K, <= 256K FLASH, > 64K RAM
                   avrtiny   - AVR Tiny core with 16 gp registers