The first step was to burn the bootloader. After a bit of research, here is what I found out:
- USBtinyISP from adafruit cannot program chips with more than 64K of flash (see this thread);
- if you don't want to start from scratch (that is, compile the source code and figuring the fuses) there are at least 3 sources: ryanmsutton, maniacbug and calunium;
- USBtinyISP half-works: it writes to the flash, but reading back for verification purpose fails because of a bug in the firmware; I ignored the verification error;
- although burning the bootloader (any of the three mentioned above) seemed successful, uploading any sketch afterwards always failed;
- the setup from ryanmsutton did not work for me (I guess the fuses are wrong; then the core files also point to the arduino folder, instead of the sanguino, as it should be);
- with the bootloader from calunium (atmega1284p_16MHz.hex) I was able to upload sketches; these are the settings in boards.txt I used:
atmega1284.name=Sanguino W/ ATmega1284p 16mhz
Note the upload protocol (stk500v1), note the fuses and note the core folder (last line).
- in the end, since the booloader from calunium worked for me, I did not try the one from maniacbug, which (from what I read on the arduino.cc forum) seems to be very popular and work very well;
defined(__AVR_ATmega1284P__) to any defined(__ATmega644P__)
#if defined(__AVR_ATmega644P__) || defined(__AVR_ATmega644__) || defined(__AVR_ATmega1284P__) // sanguino
In the end, the program space is about 126K (compared to 62K in ATmega644P) and the available RAM is 16K (compared to only 4K in Atmega644P). Not a bad upgrade for only a few bucks more.
Note: ATmega1284 is not defined in avrdude.conf shipped with Arduino 22 or 23 (folder \arduino-22\hardware\tools\avr), but it is defined in Arduino 1.0.