Which software do you use on the 84? NewSoftSerial? SoftwareSerial? Something else?
I've been using the basic SoftwareSerial but since this fine new core supports NewSoftSerial I'm going to try that as soon as I get the hardware working.
That would be nice. The biggest issue is the bootloader code overwriting itself. There are two potential solutions...
Always place the bootloader code at a fixed location in the executable image. This may not be possible.
Make the bootloader so it moves itself to one end of the Flash while the other end is programmed. This would double the wear on parts of the Flash and would be a bit complicated but would very likely work.
I naively thought we could just tell the compiler the bootloader code was to be loaded at the end of the flash- there's usually an assembly construct for that kind of thing isn't there?