Watchdog timer expired, but panic logs not seen

[Kaustubh Ashtekar]

On Wed, Sep 14, 2011 at 2:52 AM, Mulyadi Santosa
<mulyadi.santosa at gmail.com>wrote:

> Hi...
>
> On Tue, Sep 13, 2011 at 11:55, Kaustubh Ashtekar <ksashtekar at gmail.com>
> wrote:
> >
> >
> > On Fri, Sep 9, 2011 at 5:51 PM, sandeep kumar <coolsandyforyou at gmail.com
> >
> > wrote:
> >>
> >> Hi all,
> >> I wanted to manipulate the watchdog timer driver to see how it works in
> >> deadlocks.
> >
> >
> >>
> >> <snip>
> >
> >
> >>
> >> My question is this,
> >> When watch dog timer expires(hardware watchdog), its interrupt directly
> >> resets the system
> >> (or) it is treated as an interrupt and a handler is executed.
> >
> > AFAIK, after the watchdog is triggered, the SoC/processor is completely
> > reset including all the peripherals. The main purpose of a watchdog is to
> > reset a processor which has locked up somewhere in some thread (with
> > interrupts disabled, maybe), effectively starving the thread which is
> > supposed to reset the watchdog periodically.
>
> Just to add, AFAIK watchdog is used in "locked" scenario because it
> can't be masked and disabled...and it receives highest priority in
> trap/interrupt by the processors.
>

> AFAIK too, in most scenarios, handler is placed to picked up watchdog
> signal...and it is this handler which is then fix the situation.
>

AFAIK, this feature and maybe some other additional features (like Early
wakeup) are implementation dependant. Also, for e.g. if code area and/or
data area is corrupted due to any reason then even this non-maskable
interrupt would not be able to fix the situation.

The watchdog's basic idea is to hardware (soft reset) the processor and the
peripherals (through the RESET_OUT signal). Some additional features for
e.g. of a periodic interrupt before some time the watchdog actually expires
may be present in some implementations. This interrupt can be used either to
reset the watchdog timer or maybe to do a core dump, for later debugging,
before the system actually goes into a watchdog reset.

This watchdog features best use case is in embedded systems which where
there may not be any human to manually reset the system, in case it is
locked up.


Kaustubh
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