Re: [Linuxptp-users] [Linuxptp-devel] linuxptp result doesn't match 1PPS measurement

[Hamilton A. <ale...@gm...>]

Hi, Miroslav:
I am using calnex to test ptp. calnex can mimic the long path delay so it
is reasonable.
I am using switch chip, it has MAC timestamping and rx_delay, tx_delay are
compensated.

Thanks
Alex

Miroslav Lichvar <mli...@re...> 于2022年9月8日周四 21:26写道：

> On Thu, Sep 08, 2022 at 07:41:53PM +0800, Hamilton Alex wrote:
> > ptp4l[130171.662]: rms    1 max    2 freq    -49 +/-   3 delay  9058
> +/-   0
>
> > my board has 1PPS output, I connect it to the master and compared with
> > reference PPS.
> > however,  the 1pps time error is around 40 NS, which means my board is
> > ahead of the reference for about 40NS, which doesn't match the result
> > dumped by ptp4l.
>
> ptp4l is just printing the measured offset. It doesn't know the actual
> error.
>
> A measured delay of 9 microseconds is huge. That's few kilometers of
> cable. What hardware do you use? Does it have PHY or MAC timestamping,
> and are those errors compensated?
>
> --
> Miroslav Lichvar
>
>