[ntp:questions] Running ntpd with PPS precision signal only

unruh unruh at invalid.ca
Wed Feb 29 15:58:56 UTC 2012

On 2012-02-28, alex n <alexvm22 at gmail.com> wrote:
> Hi,
> I have embedded system based on ARM and FPGA. GPS receiver is connected to
> ARM (NMEA) and FPGA (PPS). There is a TXCO on board also which is using by
> FPGA as clock. PPS passes to ARM through **FPGA so I can generate my own
> PPS' based on original PPS with high accuracy and sinchronized with UTC.
> After start PPS' is adjusted and ntpd uses NMEA and PPS' as source clock.
> So how should I configure ntpd for running with PPS precision signal only
> (for case if GPS is loss)?

?? If nmea is lost, ntpd will continue to use the PPS with the local
clock supplying the "seconds" to label which second the PPS is
associated with . Unless your local clock jumps by over a second
suddenly, that will be perfect. Ie, the nmea is ONLY useful in making
sure that your local clock is within 1 second of the true time. 

> Thanks,
> Alex

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