Can I find out exactly which version of the bootloader is on my arduino? It is a genuine Arduion Uno R3 - do they all come with the same bootloader? And my real question is: Does that bootloader have the code to clear the watchdog timer interrupt so I can reset the arduino with the watchdog, but not get in an infinite watchdog reset loop? (Maybe simplest thing is just to try the watchdog and see what happens).
(holding envelope to head) "Karnak says ..."
In the IDE, select File:Preferences (I think) and turn on the Verbose buttons.
Then download a simple sketch. I think part of the output will say what bootloader it is.
I don't know on the watchdog part.
I'm not sure if the verbose output would be totally definitive.
I think the only way to be sure would be to use avrdude to read the bootloader from the chip (you would need an ICSP programmer) and do a file compare of the resulting file to the various bootloaders (in .hex format). And even that would be fiddly as you might need to exclude stuff (eg. trailing zeroes) that are on the chip but not in the bootloader .hex file.
However I think that the bootloaders shipping with the Rev3 Unos have the bug fixed about the watchdog timer.
The question is "which bug?" :-). I want to get into the bootloader by triggering a reset with the watchdog timer. Unfortunately, experimentation seems to reveal that the bootloader I have contains the logic which says "Oh, you hit a watchdog interrupt, you must want to go directly back to your sketch".
I guess I'll have to learn how to diddle and replace the bootloader (or add extra hardware to trigger the reset pin externally) if I want to get into the bootloader via sending a command to my sketch.
What we really need is a bootload that reads the eeprom to discover various option flags like how long to wait, what to do on watchdog interrupt, etc.
None of the boot loaders ever shipped with an atmega328-based UNO has ever had the watchdog problem that caused an infinite boot loader loop. The older 2k boot loader had it, and the MEGA boot loader has it, but not any optiboot.
Optiboot does turn off the watchdog and restart the sketch after a wdt. If you wanted it to load me code, you'll have a problem.