Signature bytes are in avrdude.conf.
Copy the 1284 section or another 644 section with a new name and update the memory size and signature bytes.
Make a new section in boards.txt to match.
Signature bytes are in avrdude.conf.
Copy the 1284 section or another 644 section with a new name and update the memory size and signature bytes.
Make a new section in boards.txt to match.