[ntp:questions] Re: Garmin GPS 18 firmware update -> 200ms offset

David Schwartz davids at webmaster.com
Tue Nov 29 01:13:59 UTC 2005


"Ulisses" <ulisses.alonso at unavarra.es> wrote in message 
news:20051125155350.GA27426 at s163m108.unavarra.es...

> On Fri, Nov 25, 2005 at 03:58:54PM +0100, Roman Mäder wrote:
>> thanks to all who responded. It wasn't the pps signal that had the 200ms
>> offset, but the NMEA-derived time itself. It looks like some hiccup,
>> because after another hard reset (pulling the plug) the unit is back to
>> normal operation.
>
> ummm... this makes me remember what happens with Garmin HVS-35:
>
> NMEA messages had an offset of [400, 700] ms with respect to the pps 
> pulse!
>
> I tested this in different units with an osciloscope.
>
> I asked Garmin and they told me that it was spected ¿?

    You should *not* use the NMEA messages for a timestamp unless the GPS 
unit provides some guaranteed relationship between those messages and the 
UTC secound boundary.

    DS





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