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Re: [gpsd-users] Garmin 18X-5Hz
From: |
Miroslav Lichvar |
Subject: |
Re: [gpsd-users] Garmin 18X-5Hz |
Date: |
Thu, 11 Aug 2016 16:07:06 +0200 |
User-agent: |
Mutt/1.6.2 (2016-07-01) |
On Wed, Aug 10, 2016 at 10:28:54AM -0700, Gary E. Miller wrote:
> Roger Oberholtzer <address@hidden> wrote:
> > The Garmin 18x-5Hz LVC seems to provide 'five-pulse-per-second'
> > information. I am guessing this related to the 5Hz NMEA records.
>
> Only vaguuely related. The rate of each can be independently selected.
If the rate of NMEA messages is equal to the PPS rate, I think it will
be easier to assign reference time to the pulses. If the PPS rate is
higher (as with some u-blox modules that allow rates up to 1000 Hz),
gpsd will need to count pulses between NMEA messages.
> > Is this any problem for gpsd and time synchronization?
>
> On theory, no. In practice, never tested.
gpsd supports detection of 5 Hz PPS, but there is a problem that it
always sets the fractional part of the timestamp to zero, so with 5 Hz
PPS the offsets have an error of 0.0, 0.2, 0.4, 0.6 and 0.8 seconds.
There was actually a patch that tried to fix this couple years ago,
but there was no interest back then.
--
Miroslav Lichvar
- [gpsd-users] Garmin 18X-5Hz, Roger Oberholtzer, 2016/08/10
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/10
- Re: [gpsd-users] Garmin 18X-5Hz,
Miroslav Lichvar <=
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/11
- Re: [gpsd-users] Garmin 18X-5Hz, Miroslav Lichvar, 2016/08/12
- Re: [gpsd-users] Garmin 18X-5Hz, Roger Oberholtzer, 2016/08/12
- Re: [gpsd-users] Garmin 18X-5Hz, Miroslav Lichvar, 2016/08/12
- Re: [gpsd-users] Garmin 18X-5Hz, Roger Oberholtzer, 2016/08/12
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/12
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/12
- Re: [gpsd-users] Garmin 18X-5Hz, Miroslav Lichvar, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/12