[ntp:questions] Fwd: Re: NetBSD GPS/PPS using 4.2.6p3

unruh unruh at wormhole.physics.ubc.ca
Thu Aug 25 21:20:55 UTC 2011

On 2011-08-25, Rob <nomail at example.com> wrote:
> unruh <unruh at wormhole.physics.ubc.ca> wrote:
>>> any sense to me. Perhaps you meant the NMEA sentence used
>>> needed to be within .5 sec but again that doesn't make a
>>> lot of sense in practice as all three different gps units
>>> I've used each have large variations in NMEA time so
>>> require both fudge factor and increase in the range of
>>> values that will be accepted.
>> Nope, I meant that system time should be within .4 sec. That will not
>> matter if you use gpsd since that should accurately get the time of the
>> pps pulse from the nmea of the gps unit (assuming it is not broken like
>> some of the garmin 18x are).
> What happens with gpsd is completely unrelated to what happens when
> you use ntpd's own NMEA and PPS support.
> When you have experienced that you should be within .4 sec before PPS
> works when using gpsd, you should not project that onto ntpd and its
> PPS support.  The .4 sec check is within gpsd.

>From refclock_atom.c
 * Before this driver becomes active, the local clock must be set to
 * within +-0.4 s by another means, such as a radio clock or NTP
 * itself. There are two ways to connect the PPS signal, normally at TT

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