Hal Murray wrote:
The problem is that most of the low-cost GPS toys use the SiRF chip set. It
sucks for timing. It looks like the NMEA sentences are sent from a timer
with 100 ms ticks.
http://www.megapathdsl.net/~hmurray/ntp/GPSSiRF-off.gif
A lot of SiRFstar III based devices have a 1pps pin, but you
might have to crack them open with a hammer to find it. Claimed
accuracy is 1 microsecond, but I find my cheap bluetooth GPS
receiver is always within a few tens of ns compared to a
Navsync CW12-TIM, Rockwell Jupiter and Garmin GPS 18.
I have read some words of wisdom on the web which say
that the SiRFstar III is not suitable for use in a
GPSDO, but I can't see any reason for this.
One thing to be aware of when you are searching for
the PPS output is that the PPS duration is only 1
microsecond which makes it difficult to spot on an
analogue scope.
--
Linux 2.6.26
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