[time] Garmin GPS 18 5Hz usability

Rob Janssen rob
Sun Nov 19 09:52:34 UTC 2006


Arthur Konovalov wrote:
>
> Well, due to different reasons I had to obtain GPS 18-5Hz and now ran 
> into problems...
>  From my point of view 5Hz has 2 differences compared to LVC:
> - PPS (GPGGA and GPRMC too) 5 times per second ( .0, .2,  .4, .6,  .8 of 
> each second) instead of 1
> - UTC timestamp hhmmss.s instead of hhmmss
>
>
> gpsd (svn) also refused to work complained about too short pps:
>
> gpsd: pps-detect (DCD) on /dev/ttyS0 changed to 1
> gpsd: PPS pulse rejected too short. cycle: 200015, duration: 100005
> ...
> gpsd: pps-detect (DCD) on /dev/ttyS0 changed to 0
> gpsd: PPS pulse rejected too short. cycle: 200020, duration: 100010
> gpsd: polling 4
> gpsd: <= GPS: 
> $GPGGA,091937.4,5926.10757,N,02442.82946,E,1,03,7.7,,M,20.5,M,,*7A
> gpsd: GPGGA sets status 1
>
>
> Is there any fundamental reason why 5Hz not working?
>   
Well, I can tell you why it is not working with gpsd (I originally wrote 
that PPS
implementation): this code does not expect this 5Hz pulse and is 
hardcoded for
1Hz PPS.  You could modify the source to handle this situation, but it 
is more
work than changing the cycle time check because the code also assumes the
ticks come in at the seconds-mark which has to be changed to the 200ms-mark.

I am not doing much work on this project anymore, but you could bring up the
problem and/or your solution at the gpsd developers mailinglist.

Rob



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