On Sat, Aug 29, 2015 at 08:35:56PM +0100, Guo Hao wrote: > But what if there is certain time offset between GPS clock's ToD and host > PC's ToD, say 3 us when the capture card gets its initial ToD from the PC. > Then even the capture has 1-PPS from the GPS clock, the timestamp > difference would be in the range of 3 us?
The ToD is really only telling your endace card the *approximate* date and time. Your endace card phase locks (not just frequency locks) to the PPS. Endace said: > Yes, your understanding is correct: the host clock sets the DAG’s initial > TOD for time stamping and the PPS keeps the oscillator on the DAG from > drifting. This way once the initial TOD is established if the DAG has > proper sync the largest possible timing skew would be a few > nanoseconds. and I said: > # 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. See how you got the same answer twice? > As far as I know, the GPS clock might already did something about the > egress and ingress latency. And just how do you know that? (It cannot possibly know the ingress latency of the Endace card.) > Therefore, I guess most of the latency might be introduced by the capture > card. Could be. Cheers, Richard ------------------------------------------------------------------------------ _______________________________________________ Linuxptp-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linuxptp-users
