[ntp:questions] high precision tracking: trying to understand sudden jumps

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Tue Apr 1 18:29:52 UTC 2008

>>> The basic idea is to do the time stamping in hardware deep in
>>> the network adaper.  That avoids lots and lots of jitter.
>>Yes, PTP can yield an accuracy better than 100 ns if both the NICs at the
>>clients and the server support hardware timestamping of sent/received PTP
>I am still confused. To timestamp you have to read the computer's clock.
>That is a software operation-- reading the counter in the cpu, translating
>to time, returning the result through the kernel, etc. That has all kinds
>of variable latencies,etc. I am having trouble seeing 100ns. Also seeing
>the PPS from the hardware clock and its interrupts. Or are you replacing
>all of the hardware and software of the system? (new kernel, new interrupt
>system, new nics, etc)

You can build a clock into the network adapter and sync it up to the
system clock.

These are my opinions, not necessarily my employer's.  I hate spam.

More information about the questions mailing list