[ntp:questions] Re: gps; why pps?

Brian Garrett mgy1912 at cox.net
Tue Mar 28 23:22:47 UTC 2006

"Folkert van Heusden" <folkert at vanheusden.com> wrote in message
news:20060328155232.GP26463 at vanheusden.com...
> Hi,
> Could someone please explain me why you want to only use the PPS signal
> of a GPS receiver and not the time indication?
> Folkert van Heusden
> --
Presumably because of the GPS receiver's tendency to delay the time display
anywhere from a half-second to two seconds behind the actual time.  The
processor's man task is calculating location and its firmware is dedicated
to that; by the time it gets around to spitting out time-of-day info, the
moment has passed.  Even using the raw NMEA data can get you into trouble if
you aren't clear about whether each sentence pertains to the second just
passed, or the one coming up.

Brian Garrett

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