What about the master reference? Is there any cheap implementation yet?
Daniel
Em 06/06/2013 21:48, Bob Camp escreveu:
Hi
1588 compatible network cards are capable of time stamping everything that goes
in and out. They are pretty common these days both as stand alone cards and as
peripherals on MCU's. There's no real need to do hardware, just come up with
drivers (and all the other software goop) to make them work with NTP. More or
less the same work you would have had to do once the FPGA was done and debugged.
Bob
On Jun 6, 2013, at 8:32 PM, Ralph Smith <[email protected]> wrote:
On Jun 6, 2013, at 1:59 AM, Chris Albertson <[email protected]> wrote:
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.
The Net4501 is capable of about 1/8 microsecond performance, the limiting
factor here is clock granularity.
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.
If you look at PHK's code in FreeBSD this is what is done. The PPS signal gates
the timer, so no interrupt is involved in the time stamp precision. But yes, it
would be interesting to do something on a FPGA. Unfortunately I wouldn't be
able to get to anything like that myself in this lifetime.
Ralph
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
