[ntp:questions] Time synchronization

Dahal Runa rxd1271 at louisiana.edu
Fri Feb 6 17:35:32 UTC 2009


We are using a highly accurate (GPS RT3000) and we are synchronizing our
system's time using the NTP computer. The time synchronization is pretty
accurate But we are receiving high offset and jitter values in moxa(UC-7112
plus) therefore we are not able to replace the moxa with the NTP.By using ntpq
-p the offset and jitter values obtained in NTP computer is:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
+SHM(0)          .NMEA.           0 l    2   16    7    0.000   -0.829   0.479
*SHM(1)          .PPS.            0 l    -   16    7    0.000   -0.899   0.158

and as for the MOXA board using ntpq -p we obtained the following offset and
jitter values:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*SHM(0)          .NMEA.           0 l    -   16    3    0.000   -0.058   0.416
 SHM(1)          .PPS.            0 l    -   16    3    0.000   -0.648   0.294

the following messages were received on the moxa board on running the GPSD in
debug mode:

gpsd: Packet discard of 35, chars remaining is 0 = 
gpsd: <= GPS: $GPZDA,220649.000,05,02,2009,,*51
gpsd: pps-detect (DCD) on /dev/ttyM0 changed to 0
gpsd: PPS pulse rejected. No fix.
gpsd: pps-detect (DCD) on /dev/ttyM0 changed to 1
gpsd: PPS pulse rejected. No fix.
gpsd: polling 4
gpsd: Read 35 chars to buffer offset 0 (total 35):
244302e3030302c30352c30322c323030392c2c2a35390d0a
gpsd: Packet discard of 35, chars remaining is 0 = 
gpsd: <= GPS: $GPZDA,220650.000,05,02,2009,,*59
gpsd: pps-detect (DCD) on /dev/ttyM0 changed to 0
gpsd: PPS pulse rejected. No fix.
gpsd: pps-detect (DCD) on /dev/ttyM0 changed to 1
gpsd: PPS pulse rejected. No fix.
gpsd: polling 4
gpsd: Read 35 chars to buffer offset 0 (total 35):
2447505a44412c3232303635312e3030302c30352c30322c323030392c2c2a35380d0a
gpsd: Packet type 1 accepted 35 =
2447505a44412c3232303635312e3030302c30352c30322c323030392c2c2a35380d0a7505a44412c3232303635302e3030302c30352c30322c323030392c2c2a35390d0a
gpsd: Packet type 1 accepted 35 = 2447505a44412c3232303635
gpsd: Packet discard of 35, chars remaining is 0 = 
gpsd: <= GPS: $GPZDA,220651.000,05,02,2009,,*58
gpsd: pps-detect (DCD) on /dev/ttyM0 changed to 0
gpsd: PPS pulse rejected. No fix.

on running the ntpdc query program we got the following result:

ntpdc> kerninfo
pll offset:           -0.002838 s
pll frequency:        35.740 ppm
maximum error:        0.029256 s
estimated error:      0.015308 s
status:               0001  pll
pll time constant:    0
precision:            1e-06 s
frequency tolerance:  512 ppm
pps frequency:        0.000 ppm
pps stability:        512.000 ppm
pps jitter:           0.0002 s
calibration interval: 4 s
calibration cycles:   0
jitter exceeded:      0
stability exceeded:   0
calibration errors:   0



ntpdc> loopinfo
***Warning changing to older implementation
offset:               -0.003678 s
frequency:            40.670 ppm
poll adjust:          30
watchdog timer:       6 s


ntpdc> sysinfo
system peer:          SHM(1)
system peer mode:     client
leap indicator:       00
stratum:              1
precision:            -7
root distance:        0.00000 s
root dispersion:      0.02675 s
reference ID:         [PPS]
reference time:       cd35cdf3.c3448062  Fri, Feb  6 2009  4:43:31.762
system flags:         auth monitor ntp kernel stats 
jitter:               0.014694 s
stability:            1.008 ppm
broadcastdelay:       0.003998 s
authdelay:            0.000000 s


ntpdc> sysstats
time since restart:     945
time since reset:       945
packets received:       262
packets processed:      0
current version:        0
previous version:       243
bad version:            0
access denied:          0
bad length or format:   0
bad authentication:     0
rate exceeded:          0

On moxa we are using the firmware version V1.0. I would like to know whether
such kind of output can be expected for such kind of hardware? Is it possible
to use it in place of NTP Computer?






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