Re: [Linuxptp-users] Expected throughput of the ptp4l

[Chandra M. <sma...@al...>]

Hi Miroslav & Richard,

Not sure whether I have understood your concern here.

High quality PLLs offer stepping in pico seconds.

512 sync packets are a reasonable rate for frequency corrections. In case of ToD, the fractional HW arithmetic (2^-16) can give you capability to achieve the highest accuracy possible, if the stack can supply such fine-grained values.

As for 'what is that supposed to achieve?', in ideal scenario, targeting 50pbb for CDMA is what I look at. I am further trying to analyze SyncE requirements from 1588 perspective, which seems too tough at this moment due to OS scheduling jitter itself.

Please correct me as appropriate and pour in your thoughts.

Thanking you in anticipation,
Regards,
Chandra

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"Knowledge speaks, Wisdom listens"


-----Original Message-----
From: Miroslav Lichvar [mailto:mli...@re...]
Sent: Wednesday, March 18, 2015 12:44 AM
To: Richard Cochran
Cc: Chandra Mallela; lin...@li...
Subject: Re: [Linuxptp-users] Expected throughput of the ptp4l

On Tue, Mar 17, 2015 at 05:32:38PM +0100, Richard Cochran wrote:
> On Tue, Mar 17, 2015 at 04:15:46PM +0000, Chandra Mallela wrote:
> > Could you elaborate your experience with the ptp4l performance?
>
> I never tried 512 Syncs per second, nor do I see any reason to run
> such a high rate.  What is that supposed to achieve?

I'm wondering that too. Even if we assume a very unstable clock, the clock resolution and jitter would have to be somewhere in low picoseconds to -9 provide any theoretical improvement over -8.

--
Miroslav Lichvar

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