[ntp:questions] Re: Best way to harness multiple stratum 1 servers

Wolfgang S. Rupprecht wolfgang+gnus20060406T051928 at dailyplanet.dontspam.wsrcc.com
Thu Apr 6 12:49:12 UTC 2006

Terje Mathisen <terje.mathisen at hda.hydro.com> writes:
> The next step is to build a 10 MHz (or faster!) counter which will
> reset on each PPS signal, then count until latched by a read signal
> from the NTP server. This allows you to get rid of the variable
> interrupt latency problem.

I'd be tempted to do it the other way around - have the counter
free-running and latch the count on each PPS.  That way missed PPS
events (as unlikely as they are) wouldn't mean a slipped clock and
fractional counts wouldn't be lost.  One could also read the clock at
any time and apply the scaling and offset to get the current precise

I am still hoping that at one point the GPS-on-a-chip manufacturers
will provide a fast/painless way to read the GPS chip's internal
counter and correction factors via the chip's external bus.  

This gps chip below is used in <$100 consumer gps's. With a bit of
cooperation from the company it should be possible to put it on a pci
card with a PCI-to-ARM bus coupler.  (Or maybe PCI-e, because it uses
fewer pins?)


Wolfgang S. Rupprecht                http://www.wsrcc.com/wolfgang/
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