Q wrote:
I wonder if someone would be kind enough to help me out a little here. I
have done lots of googleing and found nothing that helps me out with the
issues I'm seeing.
I am trying to reduce the PPS offset & delay (Which seem quite high for a
local device) and stop the NMEA driver from swinging and becoming a false
ticker.
Any ideas please would be great. This is only a personal project, but I was
expecting slightly better results! Below are debug outputs, configs and some
other 'useful' stuff if you could take a look over them and let me know what
I could be doing wrong, or would otherwise benefit from changing.
Cheers!
GPS;
GPS18x - NMEA outputting GPRMC to serial port.
GPS18x - PPS outputting to Pin 1 of serial port.
BAUD Rate - 115200, 8N1
NMEA Sentences output - GPRMC
PPS Length: 200msec
PPS Mode 1Hz
NMEA Output time - 1 sec
NMEA Mode 2.30 - ON
Using NetBSD-5
I found gpsd useful for debugging but just used the normal gps
type 20 driver and type 22 for pps
######
tos mindist 0.4
server 127.127.20.0 mode 1 prefer minpoll 6 maxpoll 8
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
#######
For some time I was using parallel port for pps but didn't
find much difference parallel/serial or kernel/ppsapi.
Offset would be a few microseconds.
There are differences between versions of ntpd so that required
fudge values may not be same.
David
Machine;
Very old AMD Duron 1Ghz CPU
384Mb RAM
Serial - '3: uart:16550A port:000002E8 irq:3 tx:20052 rx:32887544 fe:976
pe:1318 brk:3 oe:132 RTS|DTR'
gpsd;
Sample of debug output (/usr/local/sbin/gpsd -n -b -N -D2 /dev/ttyS3)
gpsd: speed 115200, 8N1
gpsd: gpsd_activate(): opened GPS (fd 4)
gpsd: NTPD ntpd_link_activate: 1
gpsd: /dev/ttyS3 identified as type Generic NMEA (0.107275 sec @ 115200bps)
gpsd: => Probing device subtype 0
gpsd: GPS on /dev/ttyS3 is offline (0.000727 sec since data)
gpsd: PPS cycle: -753943806, duration: -753943806 @ 1293067869.993730
gpsd: PPS pulse rejected
gpsd: PPS cycle: -753743809, duration: 199997 @ 1293067870.193727
gpsd: PPS pulse rejected
gpsd: => Probing device subtype 1
gpsd: GPS on /dev/ttyS3 is offline (0.000267 sec since data)
gpsd: PPS cycle: 1000010, duration: 800013 @ 1293067870.993740
gpsd: PPS pulse rejected
<some log missing because its just too long to post here>
gpsd: GPS on /dev/ttyS3 is offline (0.000185 sec since data)
gpsd: PPS cycle: 999985, duration: 799986 @ 1293067891.993654
gpsd: PPS cycle: 999986, duration: 200000 @ 1293067892.193654
gpsd: PPS pulse rejected
ntp.conf;
restrict default kod nomodify notrap nopeer noquery
restrict 127.0.0.1
server Private1
server Private2
server Private3
server Private4
server Private5
server Private6
server Private7
server Private8
server Private9
server Private10
server Private11
broadcast 224.0.1.1 key 6
manycastserver 239.255.254.254
#Local Clock
server 127.127.1.0
fudge 127.127.1.0 stratum 10
#NMEA
server 127.127.28.0
fudge 127.127.28.0 time1 0.500 refid GPS
#PPS
server 127.127.28.1
fudge 127.127.28.1 refid PPS
driftfile /var/lib/ntp/drift
keys /etc/ntp/keys
trustedkey 6
Output of 'ntpq -p' (Several days clean running);
remote refid st t when poll reach delay offset
jitter
==============================================================================
+Private1 .GPS. 1 u 984 1024 377 14.012 0.205 0.101
-Private2 .GPS. 1 u 1017 1024 377 14.113 0.393 0.445
-Private3 .GPS. 1 u 974 1024 377 9.706 0.208 0.256
-Privat4 .MSF. 1 u 1013 1024 377 10.875 1.662 0.040
-Private5 .PPS. 1 u 1020 1024 377 19.916 -0.660 0.475
-Private6 .DCFa. 1 u 1004 1024 377 9.496 0.276 0.226
-Private7 195.66.241.2 2 u 1004 1024 377 14.690 0.970 0.163
Private8 .GPS. 1 u 5h 1024 0 23.721 -0.517 0.000
-Private9 .PPS. 1 u 1022 1024 377 14.671 -3.016 0.012
+Private10 .PPS. 1 u 1006 1024 377 15.811 -0.262 0.020
-Private11 .CDMA. 1 u 56 1024 377 86.819 -4.640 0.101
NTP.MCAST.NET .MCST. 16 u - 64 0 0.000 0.000 0.001
LOCAL(0) .LOCL. 10 l 40 64 377 0.000 0.000 0.001
xSHM(0) .GPS. 0 l 57 64 377 0.000 -35.284 19.872
*SHM(1) .PPS. 0 l 32 64 377 0.000 -0.488 0.046
At the moment the NMEA is being reported as a flase ticker - the offset
swings violently from + to - sometimes its a valid ticker, others it not.
A few more readings - after the poll
xSHM(0) .GPS. 0 l 18 64 377 0.000 -33.130
19.161
*SHM(1) .PPS. 0 l 59 64 377 0.000 -0.542
0.063
xSHM(0) .GPS. 0 l 10 64 377 0.000 -45.655
15.924
*SHM(1) .PPS. 0 l 48 64 377 0.000 -0.541
0.051
xSHM(0) .GPS. 0 l 27 64 377 0.000 -26.448
13.995
*SHM(1) .PPS. 0 l 1 64 377 0.000 -0.573
0.060
If I give it another half hour the NMEA will be 'ok' and the offset would
have swung the other way into +ive land.
Now I know that NMEA is 'slow' but I wouldn't of expected it to wander all
over the place like that.
The PPS also appears to have a rather large offset - If I fudge it it will
break in a nasty way.
All of those stats are after a good few days running without being touched -
I have mrtg graphs if they are of any help.
Fresh from an ntp restart I get the following;
SHM(0) .GPS. 0 l 10 64 7 0.000 -12.028
18.019
SHM(1) .PPS. 0 l 10 64 7 0.000 -0.763
0.034
-SHM(0) .GPS. 0 l 20 64 17 0.000 -14.131
13.111
*SHM(1) .PPS. 0 l 18 64 17 0.000 -0.755
0.033
-SHM(0) .GPS. 0 l 58 64 17 0.000 -14.131
13.111
-SHM(1) .PPS. 0 l 56 64 17 0.000 -0.755
0.033
*SHM(0) .GPS. 0 l 14 64 37 0.000 -36.112
17.250
+SHM(1) .PPS. 0 l 12 64 37 0.000 -0.576
0.199
+SHM(0) .GPS. 0 l 21 64 77 0.000 -16.348
12.642
*SHM(1) .PPS. 0 l 20 64 77 0.000 2.978
3.713
+SHM(0) .GPS. 0 l 9 64 177 0.000 -27.085
10.346
*SHM(1) .PPS. 0 l 8 64 177 0.000 4.194
4.527
xSHM(0) .GPS. 0 l 1 64 377 0.000 -37.895
16.898
*SHM(1) .PPS. 0 l 2 64 377 0.000 6.115
5.954
'ntpq -c rv'
assID=0 status=09b4 leap_none, sync_telephone, 11 events,
event_peer/strat_chg,
version="ntpd 4.2....@1.1570-o Sat Dec 19 00:58:16 UTC 2009 (1)",
processor="i686", system="Linux/2.6.18-194.11.3.el5", leap=00,
stratum=1, precision=-20, rootdelay=0.000, rootdispersion=14.620,
peer=23623, refid=PPS,
reftime=d0c347f4.c01e663d Mon, Dec 27 2010 17:14:28.750, poll=6,
clock=d0c34822.437c3419 Mon, Dec 27 2010 17:15:14.263, state=4,
offset=3.465, frequency=-20.530, jitter=6.901, noise=7.660,
stability=0.189, tai=0
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