[ntp:questions] Garmin GPS 18LVC Setup but questions on best way

Unruh unruh-spam at physics.ubc.ca
Wed Dec 31 05:15:52 UTC 2008


George R. Kasica <georgek at netwrx1.com> writes:

>On Tue, 30 Dec 2008 21:40:27 GMT, Unruh <unruh-spam at physics.ubc.ca>
>wrote:

>>George R. Kasica <georgek at netwrx1.com> writes:
>>
>>>>>>What am I doing wrong here when I add back GPS data to break this
>>>>>>thing???
>>>>
>>>>
>>>>>Next step....I added back GPS NEMA data without the gpsd daemon (I
>>>>>don't pass the data out to anywhere so there's no real need for it)
>>>>
>>>>What does "I added back GPS NMEA" mean? What program did you use to do
>>>>that? What reads teh NMEA data and passes it on to ntp.
>>>Put the config lines back in ntp.conf so it would read the NMEA data.
>>
>>>>># ntpq -p
>>>>>     remote           refid      st t when poll reach   delay   offset
>>>>>jitter
>>>>>==============================================================================
>>>>>xGPS_NMEA(0)     .GPS.            0 l   13   16  377    0.000  -616.37
>>>>>10.466
>>>>
>>>>Looks to me like you could get rid of that offset with a fudge.
>>>What would be a good amount to use half the avg. erorr or ??
>>
>>>>>I have good PPS and am getting GPS NEMA in as well but the offset for
>>>>>the NEMA data seems quite large....what would I do to fix that??
>>>>
>>>>Use the fudge to get rid of that offset. nmea is very very slow. And I
>>>>suspect that you are having the Garmin report a huge number of nmea
>>>>sentences. That takes along time to parse. 
>>>>
>>>>And it does not report on the resulting time until the sentences finish.
>>>>Having just the one standard sentence would reduce that time.
>>>How would I get that to occur? I don't see a way to cut down on the
>>>data sent by the unit....
>>
>>
>>Yousend it an NMEA sentence telling it to not report those sentences you do
>>not need. 
>>
>>Setup minicom to listen to the serial port and display the output to your
>>screen so you can see which sentences are actually being reported. Then 
>>send it the sentences to tell it to switch off the ones you do not need.
>>
>>The PGRMO NMEA sentence tells teh garmin to switch off or on the sentence.
>>EG sending
>>PGRMO,,2<CR><LF>
>>(all MUST end with carriage return line feed) will disable all sentences. 
>>That doing
>>PGRMO,GPRMC,1<CR><LF>
>>will enable just the GPRMC sentence.
>> 
>>(The first argument is teh sentence to affect, the second is
>>0=disable,1=enable, 2=disable all, 3=enable all)
>>
>>I found that the easiest way was to construct the sentence in a file,
>>putting the <CR><LF> at the end of the file, and then cutting and pasting
>>into the minicom terminal program.
>OK I set that up to just send the GPRMC data  here but it seems to
>have made little difference in the GPS offset.

OK, I give up. I have no idea why your are getting a 700ms offset.



>(left some servers out)

>]# ntpq -p
>     remote           refid      st t when poll reach   delay   offset
>jitter
>==============================================================================
>xGPS_NMEA(0)     .GPS.            0 l    6   16  377    0.000  -667.14
>11.102
>*SHM(0)          .PPS.            0 l   14   16  377    0.000    4.673
>0.908
>+eagle-local     192.168.1.2      3 u   43   64    7    0.112   33.566
>0.633
>+apollo-local    192.168.1.1      3 u   42   64    7    0.248   -4.073
>0.729




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