Watchdog Reset

[Dennis G. Rears FSAC]

Recently my Sun 4 went down with the mysterious message "watchdog reset".
I looked at all my Sun manuals and found only a few references to it.
They all were for resetting the eeprom or nvram on what action to take
when a "watchdog reset" happens.   Does anybody have any idea what a
watchdog reset is?  In what manual is it fully explain.  Please email to
me as I don't read this list that much.  (I barely have time to browse.

[[Ed's Note: v8n118 has quite a bit of material some of which I have
included below. -bdg]]

X-Date:    Wed, 30 Aug 89 19:31:47 PDT
X-From:    beau at ultra.com (Beau James {Manager - SW Devel - Ultra Networks})
X-Subject: Re: Watchdog reset

[What is...?]

A "Watchdog reset" occurs when the watchdog timer (a hardware circuit) on
the CPU board detects that the processor is halted.  The processor is
restarted and vectored into the PROMs at the watchdog reset handler, which
prints the "Watchdog reset" message on the system console.

[Causes?]

It can be a bad CPU board.  Or it could be provoked by bad hardware - CPU,
memory, or perhaps a peripheral.  But it can also be a software problem.
Probably the most common cause of processor halts is double bus faults.
That is, the processor gets a fault trap while processing a fault trap.
The most common cause of this is overflowing the stack - especially the
interrupt stack.