Re: [Linuxptp-users] MPC8308rdb

[Chris L. <cl...@gm...>]

On Tue, Apr 23, 2013 at 2:00 AM, Richard Cochran
<ric...@gm...>wrote:

> On Mon, Apr 22, 2013 at 05:18:30PM -0400, Chris LaRocque wrote:
> >
> > Could one of you kind folks point me toward the files where the gianfar
> > timer functionality could or would be implemented?
>
> - kernel/time/posix-clock.c
> - drivers/net/ethernet/freescale/gianfar_ptp.c
>
> > Was / is there an example or two which would show me the light?
>
> You can see the original version at
>
>  https://lists.ozlabs.org/pipermail/linuxppc-dev/2010-May/082433.html
>
> but this was before the posix clock idea came along.
>
> > I need to know the magnitude of the task before I take this info to
> > management.
>
> Maybe you can just use normal timers using CLOCK_REALTIME or
> CLOCK_MONOTONIC?
>
> This what I recommend. PHC timer support has been designed into the
> API, but it has not been implemented. There are two reasons why it is
> still missing.
>
> First, adding the logic would be a non-trivial exercise (see how the
> hrtimer stuff works, to get an idea).
>
> Second, it is doubtful whether having direct PHC timers would perform
> much better than just synchronizing the system clock to the PHC, and
> using normal timers.
>
> I did a whole paper on that second point, and I am convinced that it
> just isn't worth the effort to implement PHC timers. However, I would
> support the addition of the code, if you or someone else wants to
> develop it.
>
> HTH,
> Richard
>
Thank You

I have already looked into the hrtimer source and also found the
discussions you had back in 2010 about the API. Of course I have also read
your paper. If we were just syncing the clocks I'd be done.

Unfortunately, I had counted on the alarm output to drive data acquisition
within our distributed system. I am now investigating timers and gpio to
accomplish the same goal; as long as the triggers will generate and queue
the timestamps the project will succeed. I'm just not as far along as I had
believed.

Your comment about multiplexing of the pin function is apropos. I should
have recognized something was amiss when TSEC_TMR_GCLK was not present on
the 1588 header. I am looking into where the changes to the config register
should be accomplished.

What would really be convenient is if I can get the tigger input to start
one of the fiper which would then toggle an alarm pin in one of two modes:
oneshot or periodic at an arbitrary interval; without interupting the
processor. I need time stamping of events occuring at rates of 1 kHz or
greater.

Pointers appreciated.

Regards Chris