Kelsey Cummings wrote:
David J Taylor wrote:
The reach = 0 suggests that the signals from the GPS are not being seen.
I'm not sure why it lost sync but I went ahead and upgraded to 4.2.7p5
from the ntp-dev port.
I'm still seeing high offset and variable jitter.
==============================================================================
xGPS_NMEA(1) .GPS. 0 l 45 64 377 0.000 -311.36 75.859
-time.sr 207.200.81.. 2 u 348 512 377 0.643 0.977 2.984
*clock.sjc.he .CDMA. 1 u 362 512 377 6.348 -2.584 0.289
Or: http://kgc.users.sonic.net/ntp_127_127_20_1-day.png
The initial spike was the last restart.
# Garmin GPS 18 LVC
server 127.127.20.1 mode 0 prefer
fudge 127.127.20.1 flag1 1
Does the GPS_NEMA driver actually make use of the PPS signal (currently
wired to DCD on serial port) at all or does it just use the GPS sentences?
I'm wired up following http://www.satsignal.eu/ntp/GPS-interface-2.png
except that I used a NPN transistor to drive the PPS led so it wouldn't
load the PPS signal.
-K
I'm guessing you aren't seeing pps.
My notes from last year might have been understandable
then but best I can decode from them now is:
# ntp.conf gps-18x-LVC
# gps0 -> /dev/tty00
# pps0 -> /dev/tty00
server 127.127.20.0 mode 1 prefer # NMEA $GPRMC
That was giving offset of about 70us.
No LED, just using pps direct to serial DCD. I'm still
suspicious cmos ttl out from the 18x-LVC might not be
good at driving rs232 as it requires at least 3mA/0.7V
pulldown.
ATOM driver and pps to serial DCD gave offset < 10us
Last check was with pps of my 18x-LVC direct to NACK of
parallel port without any extra components.
#ntp.conf
# mknod pps0 164 0 /dev/pps0
tos mindist 0.4 # I could reduce this now
server 127.127.20.0 mode 1 prefer
fudge 127.127.20.0 time1 0.651 refid GPSb
server 127.127.22.0 minpoll 4 maxpoll 6
fudge 127.127.22.0 refid PPSb flag3 1
server serv1
server serv2
server serv3
On a good day above cfg was giving offset = 0.000,
jitter = 0.002. NMEA offset/jitter are then very erratic
in order of 10s of ms.
Note for above I needed "fudge time1" and/or "tos mindist"
otherwise NMEA was deselected.
David
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