[ntp:questions] Re: HELP PLEASE::: NTP Garmin GPS 18lvc with PPS and gpsd

Steve Kostecke kostecke at ntp.isc.org
Mon Jul 31 18:32:06 UTC 2006


On 2006-07-31, sleek daelite <sleekstar at gmail.com> wrote:

> Could anyone help me with Garmin GPS 18lvc device that comes with PPS
> output. I've been trying to configure the device to achieve about 1ms
> accuracy. The specification of this device states it could achieve
> about 1ns accuracy.

According to http://www.garmin.com/products/gps18oem/spec.html the PPS
output is accurate to 1 microsecond. That's 1us.

> ntp-4.2.2p3-RC
> Debian  Kernel 2.6.16-2-486

I use Debian for most of my systems. But found that my Soekris 4801
clock was jumping a considerable amount ( > +- 20 ms) with a Linux
kernel. For that hardware I had to use FreeBSD.

There is a PPSkit patch available for some Linux kernels. It can provide
better PPS performance.

> gpsd 2.33
>
> My content of ntp.conf is:
> -------------------------------------------------------------
> server 127.127.28.0 minpoll 4 maxpoll 4
> fudge 127.127.28.0 time1 0.320 refid GPS

The GPS-18lvc is supported by the Type 20 Generic NMEA GPS Receiver
(NMEA). This driver includes PPS support. I use this for my lvc:

| # GPS+PPS using Atomized Generic NMEA driver
| server 127.127.20.0 mode 2 minpoll 4 maxpoll 4 prefer
| fudge  127.127.20.0 flag3 1    # Enable Kernel PPS

> My command line arguments for gpsd is:
> gpsd /dev/ttyS0 -n -D 5 -N 2

Why do you need gpsd?

-- 
Steve Kostecke <kostecke at ntp.isc.org>
NTP Public Services Project - http://ntp.isc.org/




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