at91sam9: watchdog: period

[Boris Brezillon]

On Tue, 19 May 2015 11:01:49 +0200
Jiří Prchal <jiri.prchal at aksignal.cz> wrote:

> 
> 
> On 19.5.2015 09:14, Boris Brezillon wrote:
> > On Tue, 19 May 2015 11:07:29 +0800
> > "Yang, Wenyou" <wenyou.yang at atmel.com> wrote:
> >
> >>
> >>
> >> On 2015/5/18 16:17, Jiří Prchal wrote:
> >>>
> >>>
> >>> On 18.5.2015 09:27, Boris Brezillon wrote:
> >>>>
> >>>> Can you dump watchdog registers (using devmem) ?
> >>>
> >>> / # devmem 0xfffffe40
> >>> 0x00000000
> >>> / # devmem 0xfffffe44
> >>> 0x1FFF2FFF
> >>> / # devmem 0xfffffe48
> >>> 0x00000000
> >>>
> >> The register value is right.
> >
> > It seems correct to me too.
> >
> Not to me, I want 4s:
> [    4.675675] at91sam9_wdt: enabled (heartbeat=4 sec, nowayout=1)

There's a difference between your heartbeat (the frequency you
refresh/reset your watchdog) and the watchdog expiration time (here set
to 16 secs).
We usually set the heartbeat to 1/2 or 1/4 the expiration time, so that
we're (almost) sure we can reset the watchdog before its expiration.


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com