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

On Tue, Sep 13, 2011 at 11:55, Kaustubh Ashtekar <ksashtekar@gmail.com> wrote:
>
>
> On Fri, Sep 9, 2011 at 5:51 PM, sandeep kumar <coolsandyforyou@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