On Jul 18, 6:52 am, David Lord <sn...@lordynet.org> wrote: > jimmyterrence wrote: > > Is there a maximum fudge value above which the NMEA refclock throws > > away input? Both my 18xLVC GPS receivers output serial data about 550 > > ms after the PPS signal. That works fine with gpsd, but I've been > > trying to set up the NMEA driver with pps compiled in the 2.6.34 > > kernel and it doesn't seem to work.I thought I read somewhere that it > > accepts a max of 400 ms but I can't seem to find that anywhere. Could > > anybody tell me what the value is, and maybe point me to the line in > > refclock_nmea.c (if that's where it is) that governs that? > > I don't have a Linux system handy but I've used my Garmin > no problem from both serial and with relatively poor > performance from USB. This will have been on Ubuntu 9.04 > and up. I just created symlinks /dev/gps0 => /dev/tty00 > and /dev/pps0 => /dev/tty00. > > On NetBSD I've been trying parallel port device and hit a > problem due to a bug in ntpd (corrected in later versions > but these not available for NetBSD). For ntpd 4.2.4p6-o > ntp.conf has > > tos mindist 0.8 > > and > > server 127.127.20.2 mode 1 minpoll 6 maxpoll 8 prefer > fudge 127.127.20.2 time1 0.680 refid GPSb > > Note that in my docs it states that time2 is not used > > Without the fudge time1 the PPS doesn't kick in as time > from GPS without serial DCD is too far out. > > PPSb is currently at offset 0.019 and has been getting > more deviation from 0.000 during summer with growth of > nearby trees. Even a mast of several metres is not > likely to give any benefit for more than a couple of > years at most. Most sats I've had in view when checked > is three and I don't think that's enough. > > David
I found the time2 information at http://www.ece.udel.edu/~mills/ntp/html/drivers/driver20.html time2 time Specifies the serial end of line time offset calibration factor, in seconds and fraction, with default 0.0. Is that old information? I took that to mean that I can fudge out the difference between the pps pulse and the serial information, which in my case is about 545 ms. Also, I ran these commands: ln -s /dev/ttyS0 /dev/gps0 setserial /dev/ttyS0 low_latency ldattach 18 /dev/gps after I ran the ldattach command, it created pps0, so the next line that Hal Murray had doesn't seem to do anything on my system. I checked before, and pps0 didn't exist. r...@gps:/dev# ll pps* crw------- 1 root root 253, 0 Jul 18 09:11 pps0 I've let it run for a while, and nothing is showing up on the billboard remote refidst t when poll reach delay offset jitter =========================================== GPS_NMEA(0).GPS.0 l - 16 0 0.000 0.000 0.000 _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions