AVR 328p watchdog reset

I've been using the Arduino's watchdog timer in interrupt mode, and that works fine.
I'd now like to use it in reset mode, but I'm not clear how easy it is to break things.

Given that this is an Arduino Ethernet about a year old, is it likely that the firmware
will suppress the watchdog on reboot, and avoid an endless reset cycle? The default
reset timeout is apparently 15mS, and that's not long enough for the startup code
to reach the applications setup() function.

And if it does all go to rats, is it possible to get out of an endless loop by powering
off the Arduino? That way, I can load a working sketch over the broken one if I
have to.

Thanks - Will

I don't have any experience of bricking bootloaders, but I gather that it's the bootloader itself that causes the problem (presumably because it allows the watchdog to time out while it's running) and would be fixed by burning a bootloader with the watchdog support fixed.

I would have thought that if you do brick the bootloader, you would need to upload a 'fixed' bootloader in order to upload a sketch that turned the watchdog off. I don't know if programming via the ICSP would work in that situation - it would avoid using the bootloader, but I don't know whether it would also prevent the watchdog reset from occuring. As I see that would be your only resort, if it turns out that your bootloader isn't "watchdog compatible".

This is something that would probably be best played with using an Arduino with a removable chip such as a UNO rather than a SMD board, so that you have an inexpensive way to un-brick your Arduino in the worst case.

From the boards.txt entry for the arduino ethernet board if appears that it uses the optiboot loader, so you will be able to utilize WDT interrupts without problems.

ethernet.bootloader.file=optiboot_atmega328.hex

Lefty