Le 19/11/2016 à 21:24, Richard Cochran a écrit :
> On Sat, Nov 19, 2016 at 11:40:03AM -0500, Dale Smith wrote:
>> Interesting. Do you think it's possible to rewrite the driver to
>> use whatever HW support is available? Or is the HW so broken that
>> they had to do it in SW?
> The HW PLLs on the am335x are not stable, and so when you dial a
> non-zero frequency adjustment, the clock goes bonkers. There is no SW
> work around that I am aware of.
>
>> Yeah, if you can't wiggle an I/o pin precisely based of the 1588
>> clock, what's the point of the clock?
> Well, you can synchronize this PHC reasonably well via PTP, and then
> use phc2sys to get the system time globally correct to within a few
> microseconds, so it is not totally useless. but you are right, it is
> a shame that this HW unit is so poorly designed.
If the HW time stamping and PHC adjustments are working well, this is
not very fair.
I don't know many socs that support steering their main PLLs during
normal operations.
Even if the PLLs are not very stable, you could do very very slow
external adjustments
but you need a non negligible amount of external HW.
Regards,
Emmanuel.
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