Re: clockevent questions

[Francis Moreau]

Hi Thomas,

Thanks for answering so quickly !

On 5/12/07, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> Francis,
>
> On Sat, 2007-05-12 at 16:54 +0200, Francis Moreau wrote:
> > I'm trying to use clocksource and clockevent new subsystem. My
> > platform has a timer that I'd like to use both as a clocksource and a
> > clockevent devices.
>
> See arch/i386/kernel/hpet.c

thanks for the pointer

> > This timer is continueous in sense that it can run
> > without any interruption
>
> -ENOPARSE
>
> Has your timer a free running counter and a match register based event
> mechanism ?

yes

> > so I assume I can flag the clocksource device
> > with "CLOCK_SOURCE_IS_CONTINUOUS". However I noticed that clockevent
> > device can be stopped by using "set_mode()" method. Are these two
> > behaviours compatible ?
>
> the clock event stop only stops the event mechanism, it does not stop
> the counter.
>
> See arch/i386/kernel/hpet.c

OK. I got it now, In my initial plan, I was thinking to stop the
counter to stop the event. But that's not the right thing to do. It
seems that I should disable event interrupt instead.

> > Another question is that I have another embedded 16 bits timer that I
> > would like to use. Since the timer is only 16 bits, the maximum
> > interval is tiny, My question if a user ask for a clockevent device
> > using an interval is bigger that 2^16, the clockevent system doesn't
> > return an error. Instead it silently reduce the interval to 2^16. Is
> > this correct ? if so why ?
>
> Yes, it is correct. The generic timer code requests an event in the
> future. It does not care, whether the hardware device can handle that or
> not. So the clock event code limits the delta to the maximum delta the
> device can handle. The interrupt fires and the generic timer code
> reschedules the event with the remaining delta time.

Thanks again for explanations. Could you give me a pointer of this reschedules ?

--
Francis
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