[time-nuts] GPS clock to RT-Linux for pulsar machine

Mike Nolan nolan at naic.edu
Fri Jul 1 17:41:27 EDT 2005

On Fri, Jul 01, 2005 at 01:45:04PM -0700, David Forbes wrote:
> with the 1PPS from GPS. I expect to use NTP to get the correct second.
> Does NTP provide a way to tie an interrupt from some user-provided 
> hardware to sync up the fast clock to ~50 microsecond accuracy, or is 
> there some other method?
> Thanks in advance for any help.

For every application I've used, we use ntp to choose the second, and use
a sampler with a trigger input that gets 1 PPS ticks from the maser.
At 100 us, you might get away with using the GPS 1PPS as a trigger,
but even that would make me nervous. But I think you need a trigger on
the sampler if you care about timing.

Even that way we've had trouble: our datataking under some circumstances
slew ntp by a huge amount (like 500 PPM). That can get it off by seconds
before ntp can react.

Mike Nolan +1 787 878 2612 Fax: +1 787 878 1861 nolan at naic.edu
Arecibo Observatory, HC3 Box 53995, Arecibo, Puerto Rico 00612

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