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

[Richard C. <ric...@gm...>]

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