[SPARCbook] 3GX: Reboot wedged at 0C0 (Watchdog interrupt)

[patl at phoenix.volant.org]

On 11-Feb-00 at 18:58, Tim Strobell aka Griffy (griffy at math.umd.edu) wrote:
>  |>comes on.  The status display shows the battery charge level
>  |>and runs through the sequence: 0D0 (very briefly), 007 (for
>  |>several seconds), then 0C0 where it hangs.
> The same thing has happened to my poor Sparcbook GX as well.
> 
>  |>Every now and then
>  |>it will beep, flash a 'Watchdog reset' message and run through
>  |>the sequence again.
> I er...removed the annoying speaker, so mine doesn't beep.
> However, I don't see the Watchdog reset message, nor does mine "restart." 

Without the beep, you'd have to be watching pretty closely to
notice it.  If you just check it every now and then, you'll
only see it setting at the 0C0.

> The watchdog timer is a counter (in the NVRAM?) that the OS (PROM? OS low
> level interrupt handler?) tracks. Should the OS be hung hard, the counter
> won't get updated and the system will detect this and restart itself.
> This not-so-useful feature is available as setenv watchdog-reset? true
> in the OBP, IIRC.

Back in the original version of SunOS on the Sun 100, it was necessary
because the interrupt timer ran through a series of instructions to
ensure that the dynamic RAM was refreshed.  If you missed too many
interrupts, there was a good chance that the memory would be corrupted;
so a reset was a reasonable thing to do.

I believe it was implemented by having a second timer interrupt that
was set to occur at a longer period than the primary timer.  Every
primer timer interrupt would reset the count on the watchdog.

> My own presumption is that the counter is based on some value that has
> overflowed. Though if this were true, all SBs would have this problem.
> I think the watchdog is disabled by default. Since the NVRAM is well...
> NV (and assuming said counter is in the NVRAM) a probable solution is
> to somehow clear the NVRAM. 
> 
> Am I nuts, or does this sound feasible? :-)

I would suspect that the boot PROM and the OS would stick with the
original design and just keep resetting the watchdog on every timer
interrupt.



-Pat