[ntp:questions] garmin 18x and linux

Greg Hennessy greg.hennessy at cox.net
Fri Sep 2 10:51:29 UTC 2011


On 2011-09-02, Chris Albertson <albertson.chris at gmail.com> wrote:
> As I said,  Without a PPS signal you will not get reasonable
> results.

I would appreciate advice on solving the problem I have, not buying
the equipment you wished I have. I don't need microsecond timing. I
don't need millisecond timing. I have a need to have my clock set to
about a second, which a NMEA only gps should be able to solve.

> The problem with NMEA only setups is that (I think) the firmware takes
> non-determinic time to convert its internal data to ASCII.  This means the
> sentence is never output at the exact second "tick".   This error is enough
> to cause the GPS to fail NTPs clock selection algorithm.

With only one source, how do I verify that your suspicion is correct? 
ntpq -p shows reach never changing from zero.

> OK, no Internet at the observatory.  But try using pool servers while you
> are setting up and debugging.  You will need additional ref clocks to verify
> your GPS. 

My problem is not that my GPS reported time is bad. My problem is that
ntp is not showing it is processing any of the data. Running ntpd with
the -n and -d flags shows that input from the GPS goes into ntp, but
reach never changes from zero.


>> On 2011-09-02, Chris Albertson <albertson.chris at gmail.com> wrote:
>> > Also, don't expect any reasonable result until you connect the pulse per
>> > second to NTP.
>>
>> There is no PPS for the GPS18x PC.
>>
>> > You only listed one line from the config file.  Post more of it.   And
>> > finally it helps a lot if you can add some pool servers to the config
>> file.
>>
>> The only other line is the driftfile line. The computer is meant for
>> control of a telescope and observatory, and isn't on the
>> internet. Adding pool servers won't help for that reason.
>>
>> Given that ntp in debug mode shows gpsread showing NTP at least sees
>> the GPRMC messages, can anyone sugguest why NTP never syncs? Is there
>> additional debug flags that would be useful?
>>
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