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Re: [gpsd-dev] PPS support
From: |
Eric S. Raymond |
Subject: |
Re: [gpsd-dev] PPS support |
Date: |
Sun, 5 Apr 2015 04:58:17 -0400 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
Sanjeev Gupta <address@hidden>:
> I started using gpsd three years ago, to interface with NTP servers I am
> running for the pool. The issue I had, repeatedly, was to check if my
> devices (all cheap consumer stuff) reported a PPS, and if this was being
> passed to NTP in a usable fashion.
>
> Unfortunately, there seemed to be no way to even know reliably if the
> device was sending a PPS. The list provided lots of advice, including
> looking at SHM segments, tuning, calibration, etc. Note the problem: not
> that PPS did not work, but I did not know if it was working.
Hm. It appears that I erred in writing ppscheck and then dropping it into
the contrib directory rather than documenting it as a fully-fledged tool.
Fortunately - as you note - we fixed this by teaching gpsmon how to display
PPS bars.
> Over the last couple of months, PPS display support has become a
> non-brainer. Thanks to the developers (I am looking at you, Mr Miller), I
> have been meeting local enthusiasts, plugging their devices into my laptop,
> and in every case, seeing both a PPS display in PPS, and NTP locking onto
> it. Note that all these devices are "unbranded", bought off eBay.
Huh? What? We've had the devil's own time finding inexpensive PPS-capable
devices. Tell us more; where can we dig these up?
> killall gpsd
> gpsd -n /dev/ttyUSB0
> /etc/init.d/ntp restart
> gpsmon
> (go for a smoke)
> ntpq -pn
Gary, that looks to me like an improvement on this:
$ su - (or sudo -s )
# killall -9 gpsd ntpd
# ntpd -gN
# sleep 2
# gpsd -n /dev/ttyXX
# sleep 2
# cgps
But the technical content in the Time Service HOWTO is your baby and I don't
want to change that without clearing with you.
> Could someone who has a wider range of devices see if this item still needs
> to be in the TODO ?
> ==
> **** In gpsmon's PPS Offset field
>
> Presently PPS Offset is displayed in direct mode for NMEA, SiRF, and
> UBX devices. Others should probably do likewise, notably the
> Motorola Oncore and Garmin drivers.
It does. Garmin support is on Gary's to-do list.
> Thank you, thank you, thank you
You're welcome. I've been consciously steering the project in the direction
of supporting time service better; nice to see it's having an effect.
--
<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
Re: [gpsd-dev] PPS support, Gary E. Miller, 2015/04/05