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

[Xavier B. <xav...@fr...>]

OnThu, 19 Mar 2015 09:30:56 -0700 
<https://www.mail-archive.com/search?l=lin...@li...&q=date:20150319>, Richard Cochran wrote:

> Here is a random metric from the boards on my desk.  The CPUs are the
> TI AM335x, but using the DP83640 PHY as the PTP Hardware Clock.  The
> slave is directly connected to the master with 1 meter cable over a
> 100 Mbit link.
>
> Measuring the edges of a 1 kHz output at various Sync rates, and with
> a DelayReq rate of 1 Hz, I see the following differences.
>
>    Rate   Offset
>    ----------------
>    2^0    +/- 75 ns
>    2^-3   +/- 25 ns
>    2^-4   +/- 20 ns
>    2^-5   +/- 20 ns
>
> As expected, increasing the DelayReq rate to 2^-5 makes no difference.
>
> So with this hardware, I have already reached the limit of
> synchronization performance.  Increasing the Sync rate to 512 frames
> per second would not improve the picture.
>
> In contrast, using SyncE on the exact same hardware immediately yields
> an offset of +/- 1 nanosecond. (Actually, it probably is smaller, but
> I can't measure it with my lousy scope.)

Hi Richard,

Out of curiosity how do you use SyncE on this hardware ?
I can't see the DP83640 doing SyncE.

     Xav