The best WDT I ever seen, was an interrupt that run 10 times faster than
the WDT timer. Several routines actually update their respectively flags
at one especific memory position. The interrupt routine check those
flags and clear them. Some flags should be set by its routines much
often than others. The interrupt routine knew that and act accordingly.
If by some reason one routine fails to update its flag, the interrupt
routine was able to reset the memory pointers and data for that
particular routine and reset it without needing to reset the entire
processor. If the failing routine doesn't restart nicely, then the
interrupt routine propositaly fails to clear the WDT, it resets the
entire processor.
Wagner

Harold M Hallikainen wrote:
>
>         In terms of computers (including PICs), I don't think it's a
> question of IF they will crash, but more a question of WHEN they will
> crash.  Having a WDT allows the system to recover from the crash.  I once
> had to drive 100 miles through Kansas in the middle of the night to hit
> reset on a system I built to control broadcast transmitters so the
> station could go back on the air at 6am.  EVERYTHING I've built from then
> on includes a watchdog timer...