Re: [Linuxptp-users] Installation of Linuxptp on Ubuntu PC

[林志剛 <dun...@gm...>]

so, the unit of master offset is nanosecond?how to convert to ppb?
2015/8/30 上午2:10於 "Richard Cochran" <ric...@gm...>寫道：

> On Sat, Aug 29, 2015 at 06:09:56PM +0100, Guo Hao wrote:
> > ptp4l[7726.711]: master offset         -8 s2 freq   +3835 path delay
> > 825
> >
> > Does this mean the clock offset between the 82574 NIC and the Master
> Clock
> > is in the range less than 100 ns?
>
> Yes.
>
> > Does that mean the system time is synchronized to the ptp hardware clock
> on
> > the 82574 NIC?
>
> Yes, but remember that there is probably some offset in the low
> microseconds range.  The "delay" tells you that reading the PHC time
> over the PCIe bus takes about 13 microseconds.
>
> > However I cannot run ptp4l and phc2sys as a daemon process under Ubuntu:
> >
> > root@Hao-Ubuntu:~# service ptp4l start
> > ptp4l: unrecognized service
> > root@Hao-Ubuntu:~#
> >
> > Any idea on this?
>
> Just start the programs by hand.  To start them automatically, one
> easy way is to put the commands into /etc/rc.local.
>
> > Therefore, I doubt whether there is a inherent delay between the point
> when
> > the Ethernet capture card request for the ToD and point the Ethernet
> > capture card really gets the information or the system time is not
> > synchronized by the hardware clock of the 82574 NIC.
>
> But you said,
>
>    the Ethernet capture card gets the 1-PPS from the same GPS clock.
>
> so the ToD from the host is irrelevant.  The capture has the GPS's
> 1-PPS, and so the phase of its time stamps should be correct to a few
> hundred nanoseconds.
>
> The ~1 usec difference is probably just the sum of the GPS device's
> egress latency and the capture card's ingress latency.  The number is
> perfectly reasonable, if one or both of the devices has MAC time
> stamping.
>
> HTH,
> Richard
>
>
>
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