On 11/09/17 13:45, Miroslav Lichvar wrote:
Is there an upper bound on the latency which could be used to fix
the timestamp as if it was captured before the transmission?
Well, I guess there is a upper bound but I think it could possibly be
much larger than the mean or median value.
I think there is a requirement that both SW and HW transmit timestamps
are before the actual transmission. A timestamp captured after the
transmission could make the measured network delay shorter than it
actually is. This might be more important for NTP than PTP.
That is a pity, because I think that the callback to tx_complete will
have relatively low jitter with respect to the actual transmission. My
guess was consistency was more important than correctness; does it
matter if the measured delay is less than it actually is so long as it
is consistently off by the same amount?
Alan.
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