[time-nuts] Net4501

[Chris Albertson]

Yes, that is exactly what I meant by "remove the temperature issue"  that
means using a clock derived from a laboratory standard like GPS disciplined
OCXO or a rubidium oscillator.  Once you do this the next bottle next is
the uncertainty in the interrupt latency and the granularity of the clock
that is being sampled.  So practically you are limited to about microsecond
level performance.

I think to get better than that you need to eliminate the interrupt and
have some kind of deterministic hardware where the PPS directly samples the
counter.  Perhaps hosting NTP on a soft CPU inside an FPGA, then you could
implement the PPS interrupt in gates rather then in software.   I've not
read of anyone doing this yet.



On Wed, Jun 5, 2013 at 8:49 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

>
> albertson.chris at gmail.com said:
> > However if you can replace the CPU clock with a "time nuts grade"
> standards
> > referenced clock then the net4501 can be possibly one of the best NTP
> > servers out there.   But this can be said about any computer.  If you can
> > completely remove the temperature issue NTP becomes very stable, at the
> > microsecond level or better.  Even if such stability has no practical
> use.
>
> Don't overlook that we are interested in the temperature of the crystal,
> not
> the environment.  Even if you can hold the environment solid you still have
> to consider the local temperature changes due to CPU load.
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
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-- 

Chris Albertson
Redondo Beach, California