Sander Smeenk wrote:
Hi,
I run a stratum 1 server which has a Garmin LVC 18x connected to its ttyS0.
The GPS provides a PPS signal via serial and i use gpsd to provide the
NMEA sentences and pulse data in shared memory to NTP.
This partly works. NTP syncs against the PPS signal but the NMEA signal
is always marked as falseticker even though i managed to bring down the
offset to -1.5ųsec average by fudging the time a bit. The NMEA signal
offset fluctuates a lot. From ~ -65ųsec to ~ +75ųsec.
The GPS provides 9600bps serial comms. Would it help to speed this up to
19200bps? I've already disabled all NMEA sentence output for sentences that
"aren't useful for timekeeping" but at this moment i have to use external
clocks to sync against.
Few questions:
1) Can i get a 'true PPS sync' with this setup?
Eliminating gpsd so 'ntpq -p' shows 'oSHM(1)' instead of '*SHM(1)' ?
Hi
Jun 21, 2009: My Garmin 18x LVC gave just acceptable
performance with the NMEA driver due to having to tune the
fudge offset at almost the limit that avoided the wrong
second. For PPS I used the ATOM driver and was getting an
offset of < 6us.
Shortly afterwards Garmin released a firmware fix which
fortunately I avoided as the nmea output could over-run into
the following second.
I'd need to search my backups for the exact server and fudge
config lines.
Currently I'm running NetBSD-6/i386 and ntpd 4.2.7p476 and my
ntp.conf for a Sure GPS has:
tos minsane 3
tos orphan 10
tos mindist 0.4
server 127.127.20.2 mode 18 prefer
fudge 127.127.20.2 stratum 7 time2 0.407 flag1 0 refid GPSb
server 127.127.22.2 minpoll 4 maxpoll 4
fudge 127.127.22.2 flag2 0 flag3 1 refid PPSb
plus one local peer and four local servers
NB. the mode and fudge time2 are specific for the Sure GPS.
David
2) What could i possibly do to get NTP to sync/accept the NMEA data,
other than set it as a truechimer in the configuration?
3) Why does last_event show clock_alarm for the PPS SHM signal in assoc?
At this moment my 'ntpq -p' looks like:
| # ntpq -np
| remote refid st t when poll reach delay offset jitter
| ==============================================================================
| 127.127.28.0 .NMEA. 0 l 10 16 377 0.000 -52.910 12.585
| *127.127.28.1 .PPS. 0 l 9 16 377 0.000 -0.002 0.002
| -193.67.79.202 .PPS. 1 u 50 64 377 3.690 0.331 0.073
| +193.79.237.14 .PPS. 1 u 48 64 377 2.753 0.128 0.725
| +80.94.65.10 .PPS. 1 u 63 64 377 3.226 0.005 0.498
| -130.89.0.19 103.52.146.131 2 u 30 64 377 5.417 -0.100 0.041
| # ntpq -c rv
| associd=0 status=0415 leap_none, sync_uhf_radio, 1 event, clock_sync,
| version="ntpd 4.2.6p5@1.2349-o Wed Oct 9 19:08:06 UTC 2013 (1)",
| processor="x86_64", system="Linux/3.13.0-39-generic", leap=00, stratum=1,
| precision=-23, rootdelay=0.000, rootdisp=0.386, refid=PPS,
| reftime=d8318503.7827c0d3 Tue, Dec 9 2014 15:26:11.469,
| clock=d831850e.45ff40f3 Tue, Dec 9 2014 15:26:22.273, peer=53550, tc=4,
| mintc=3, offset=0.001, frequency=-19.125, sys_jitter=0.003,
| clk_jitter=0.001, clk_wander=0.000
| # ntpq -c as
| ind assid status conf reach auth condition last_event cnt
| ===========================================================
| 1 53549 9024 yes yes none reject reachable 2
| 2 53550 964b yes yes none sys.peer clock_alarm 4
| 3 53551 931d yes yes none outlyer 1
| 4 53552 9424 yes yes none candidate reachable 2
| 5 53553 9424 yes yes none candidate reachable 2
| 6 53554 931d yes yes none outlyer 1
Thanks for any input!
-Sander.
_______________________________________________
questions mailing list
questions@lists.ntp.org
http://lists.ntp.org/listinfo/questions
