On Mon, Aug 16, 2010 at 12:24:48PM -0700, john stultz wrote:
For PTP enabled hardware, the timestamp on the network packet comes
from from the PTP clock, not from the system time.
Of course, you can always just leave the PTP clock alone, figure the
needed correction, and apply it whenever needed. But this has some
disadvantages. First of all, the (one and only) open source PTPd does
not do it that way. Also, only one program (the PTPd or equivalent)
will know the correct time. Other programs will not be able to ask the
operating system for time services. Instead, they would need to use
IPC to the PTPd.
The PTP protocol (and some PTP hardware) offers a "one step" method,
where the timestamps are inserted by the hardware on the fly. Here you
really do need the PTP clock to be correctly adjusted.
All of the PTP hardware that I am familiar with provides a clock
adjustment method, so it simpler and cleaner just to use this facility
to tune the PTP clock.
Richard
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