[ntp:questions] Accuracy of NTP - Advice Needed

Chris Albertson albertson.chris at gmail.com
Sat Dec 24 04:13:49 UTC 2011


On Fri, Dec 23, 2011 at 5:51 PM, Mike S <mikes at flatsurface.com> wrote:
> At 01:58 PM 12/23/2011, Chris Albertson wrote...
>
>> But there is no hop of doing uS
>> level over the gigabit either net.
>
>
> IEEE 1588.

Seem 1588 can work at the sub uS level but actual real-work software
on Linux works at the "tens of uS" level.  The limiting factor is the
hardware's ability to time stamp eithernet packets.   If you have
special hardware you can get to sub-uS but not using PTPd on Linux or
BSD.

Linux's and BSD's time stamper for the PPS interface works better
(less jitter) then its time stamper for Ethernet.

In a standard Cat-5 cable there are 8 wires in 4 pair.  Ethernet only
uses 2 pair.  I simply used a "spare" pair for a pulse.   The parts
required cost under $5 assuming you have tools to build cables already
or old cables you can hack.


-- 

Chris Albertson
Redondo Beach, California


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