ppb is dimensionless, but one nanosecond is one ppb of a second, so... -Dale
On Sun, Aug 30, 2015 at 2:55 AM, 林志剛 <[email protected]> wrote: > so, the unit of master offset is nanosecond?how to convert to ppb? > 2015/8/30 上午2:10於 "Richard Cochran" <[email protected]>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 >> >> >> >> ------------------------------------------------------------------------------ >> _______________________________________________ >> Linuxptp-users mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/linuxptp-users >> > > > ------------------------------------------------------------------------------ > > _______________________________________________ > Linuxptp-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/linuxptp-users > >
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