You'll probably get better (and more interesting!) answers on the NTP
group/mailing list, but a first thought is that NTP takes quite a long
time to stabilize after startup.
From the jitter value below being larger than the offset, I'm guessing
you took this ntpq snapshot after only a few polling intervals. Give it
a couple of hours and see where you end up. (Because of the slow
convergence, the typical laptop usage pattern is not conducive to good
NTP performance.)
John
----
On 1/18/2011 3:21 PM, Mark Ngbapai wrote:
Hi all. I've grown interested in precise timekeeping so I decided to
buy an inexpensive Transystem iBlue 737 GPSr clone with MTK 3301 +
3179 chipset (32-channel, -158dBm tracking sensitivity, Silicon Wave
Bluetooth 1.2 chipset) for use with my Fedora 12 Linux Netbook (An
Acer Aspire One D150). Having lock indoors of 5/9 satellites I've
succeeded connecting the device via rfcomm to my netbook and using
gpsd for parsing the data. I restart the nptd server in the machine
and after a few minutes I get:
[root@PHOENIX Streamer]# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
*SHM(0) .GPS. 0 l - 16 377 0.000 24.511 42.977
If I execute ntpstat, it shows:
[root@PHOENIX Streamer]# ntpstat
synchronised to modem at stratum 1
time correct to within 67 ms
polling server every 16 s
In /var/log/mesages I see the lines:
Jan 18 20:38:39 PHOENIX ntpd[6898]: ntpd [email protected] Wed Dec 9
11:49:22 UTC 2009 (1)
Jan 18 20:38:39 PHOENIX ntpd[6899]: precision = 5.448 usec
Jan 18 20:39:28 PHOENIX ntpd[6899]: synchronized to SHM(0), stratum 0
So why my system is telling me the time is correct within 67 ms and
not 5.44 usec? My GPSr is located at 1-1.5 meters from my netbook
(GPSr battery lasts around 40 hours, low power is not an issue). Does
my Linux installation need special Kernel patching or I'm missing
something?
Thanks in advance,
Mark
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