[ntp:questions] Re: Bought a GPS receiver--What next?

Richard B. Gilbert rgilbert88 at comcast.net
Mon Nov 1 22:17:13 UTC 2004


W. D. wrote:

>Hi Folks,
>
>I bought this Motorola Oncore GT+ unit from 
>the affable Mr. John Gibbons:
>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5728147332
>
>It starts blinking its pulse-per-second blue LED just a
>few seconds after the power is turned on, and sounds in 
>sync with WWV on 5 mhz.
>
>I've searched through lots of documentation on how to get
>NTP (on FreeBSD) to use the PPS signal it generates, but I have
>a few questions.
>
>First of all, this page seems to be the most complete
>page for configuring GPS:
>http://www.wh7n.net/refclock/clock2.php
>
>He says that you need to rebuild the kernel, but others
>say that it's possible to get better accuracy if you don't.
>What's the real, full story?
>
>Somewhere I read that you need to load the following
>driver:
>
>   /usr/src/contrib/ntp/ntpd/refclock_oncore.c
>
>Where does it need to be loaded?  Why isn't there a 
>reference to it on the Pilikia page?  Are there
>any other things I need to know about getting
>this receiver integrated?
>
>Also, once everything is configured properly is it
>possible to talk to this unit to find out my 
>latitude, longitude and elevation?  How many satellites
>it sees?
>
>Thanks kindly for your advice!
>
>  
>
Assuming that your version of NTP (you didn't specify) was built with 
all the refclock drivers, you should be able to connect your Motorola 
Oncore GT+ to a serial port and configure it as directed by the 
documentation for that version!  I've only configured an Oncore on ntpd 
4.2.0 which requires two links, /dev/oncore.pps.0 and 
/dev/oncore.serial.0 pointing to your serial port.  Next you need 
/etc/ntp.oncore0 which is configuration file that looks something like this:
# /etc/ntp.oncore0
#
# Reference Clock configuration for Motorola Oncore M12
#
# Five Choices for MODE
#    (0) ONCORE is preinitialized, don't do anything to change it.
#          nb, DON'T set 0D mode, DON'T set Delay, position...
#    (1) NO RESET, Read Position, delays from data file, lock it in, go 
to 0D mode.
#    (2) NO RESET, Read Delays from data file, do SITE SURVEY to get 
position,
#                  lock this in, go to 0D mode.
#    (3) HARD RESET, Read Position, delays from data file, lock it in, 
go to 0D mode.
#    (4) HARD RESET, Read Delays from data file, do SITE SURVEY to get 
position,
MODE 1
#     NB. If a POSITION is specified in the config file with mode=(2,4) 
[SITE SURVEY]
#         then this position is set as the INITIAL position of the ONCORE.
#         This can reduce the time to first fix.
LAT 39 45.3753          # Positive is North.
LONG -75 04.27187       # Negative is West
HTGPS 18.28 M           # Height in meters.
SHMEM  /var/log/ntpstats/ONCORE.0
TRAIM YES               # May need this if antenna position is suboptimal.

Finally, you need to add a server statement in /etc/ntp.conf:
# Reference Clock (Motorola Oncore M12)
server 127.127.30.0 prefer

All this stuff is, AFAIK, version specific.  What I have shown here is 
working on a Sun Ultra 10 running Solaris 8.  Your mileage may vary.




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