Some days I see things that trigger my tech “fix-it” gene.
I saw this Intructable and the author mentioned the problem of programming a non-P version of the ATmega1284P processor.
I had to look at my tech notes doing this in the Arduino IDE.
It was actually the ATmega328P. I had bought 10 of the ATmega328 processors, raw chips for my Carbon Block Aquaponics project two years ago and then found out it is not supported by the Arduino IDE. This tech note saved me.
The device signature for ATmega1284P is 1E 97 05 for the ATmega1284 it’s 1E 97 06. I’m sure the same avrdude.conf edit would work with this to program the non-P processor. Let me know if you try it.