Thanks, I looked at the 584 page d/s, and decided it was easier to ask the experts!
BTW, out of stupidity, I bought a couple of the atmega1284-PU chips instead of the
atmega1284P-PU chips, and to burn the bootloader, I found I had to track down the
avrdude.conf file and change to the chip-signature to that for the 1284. Then, it
burned the bootloader ok using the ArduinoISP sketch from a UNO chip.
However, to download sketches into the 1284 bootloader chip using the IDE, I then
had to change avrdude.conf back to the original 1284P chip-signature. Interesting.
Also, thanks for building the Bobuino bootloader. It's much more Arduino
pin-compatible than the others.