I just compared the --mmcpu options of my avr-gcc 5.4.0 with [0] and I don't see any missing device family upstream. Is there a list of hardware that is only supported by the Microchip fork?
There are also patches posted to port the upstream AVR backend to CC0 (see [1]) [0] https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/AVR-Options.html [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92729
