[ntp:questions] lots of GPS modules and info at SparkFun
Ron Frazier (NTP)
timekeepingntplist at c3energy.com
Thu Feb 9 07:35:36 UTC 2012
I spent a little while skimming over the 254 PAGE! pdf of the manual
from the SparkFun website. The device is certainly well documented. I
couldn't find where they specify the timing relationship you specify.
That's very interesting if it's consistent. I'm currently using a
GlobalSat BU-353 USB only GPS, outputting only the GPGGA sentence only
at 57600 baud. I'm getting ~ +/- 15 ms peak offsets between the
computer clock and the GPS polling every 8 seconds with jitter averaging
around 3 ms.
Based on your note and some data in the Trimble manual, I've reset my
GPS to output only the GPZDA sentence. I looked at the link below to
find the mode command to set NTPD to recognize this sentence:
It turns out mode 8 does the trick, plus the other bits I add to get to
57600 baud, so it works out to mode 72. So, the GPS part of my ntp.conf
server 127.127.20.5 prefer minpoll 3 maxpoll 3 mode 72
fudge 127.127.20.5 time2 0.3550 refid GPS1
So, I'm going to let that run a while and see if it's more stable than
the GPGGA setup.
On 2/8/2012 6:37 PM, Brent Gordon wrote:
> One cool thing about the Copernicus, beside the PPS, is that the
> datasheet specifies the delay from the PPS to start for the ZDA
> sentence. This means you can use the serial data directly without
> having to use the PPS. On other GPS units I've looked at, the delay
> from PPS to ZDA varies greatly (300 ms +/- 150 ms).
> On 2/8/2012 3:23 PM, Ron Frazier (NTP) wrote:
>> Hello all,
>> While researching potential GPS modules to experiment with for PPS
>> output, I discovered that SparkFun has quite a lot of modules, some
>> of which have PPS and some of which don't. You can't necessarily
>> tell from the product page. You have to check the data sheet. You
>> can go to their website and search for gps. This link should also
>> work. Just thought I'd pass it along.
>> Here is one unit which does have PPS but it's not obvious from the
>> product page. There are others as well.
>> 12 Channel Copernicus II GPS Receiver - from Trimble -
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