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[gpsd-users] possible week rollover problem
From: |
Paul Fox |
Subject: |
[gpsd-users] possible week rollover problem |
Date: |
Tue, 25 Aug 2015 13:44:04 -0400 |
i've been seeing bad dates from gpsd which seem to indicate a week
rollover issue. i've been running gpsd 3.9, which i realize is out of
date, but which i think is more recent than most "week rollover"-related
commits i could see in the git log. (i've now upgraded to gpsd 3.15,
so i'll see if the problem described below reappears.)
i have two BU-353 usb dongles: one older (sirfstar 3?), the other a
newer S4 with a sirfstar 4. (yes, i've read the FAQ, and it's slow
to acquire sometimes, but i needed something in a hurry at the
time.) they both exhibit similar date issues with gpsd.
unfortunately, it's hard (because of the binary protocol) for me to
trivially check them against something other than gpsd.
what i've observed:
1) a few weeks ago i took a weekend trip, and the timestamps recorded
by my application for the entire trip were in 2035. comparing
closely on my return, the delta from the true time was
approximately 19.6 years. i didn't notice the problem until i
examined the trip logs days later, and by that time, the problem
was no longer occurring, so i have little other data to offer.
the laptop may or may not have been rebooted in between. (fwiw,
my logging software accesses gpsd in nmea mode.)
2) earlier today, using either of my receivers with gpspipe, and using
either -r or -w, i got dates in october of 1918. the exact delta
from true date was very close to 6 19.6 year rollover intervals.
while this was happening, gpsmon was reporting a correct date
(8/25/15) in its "Time:" field, but i don't know if that field
represents system time or gps time.
in an attempt to see whether it was my device or gpsd that was in
error, i stopped gpsd and used gpsctl to switch the device to
NMEA mode. accessing the serial port directly showed that the
device's GPRMC sentences were giving the correct 8/25/15 date.
i restarted gpsd, and the 1918 dates were gone: i now see correct
dates everywhere. so the test was inconclusive -- perhaps the
device was fixed due to the mode switch, or gpsd was fixed due
to the restart.
if this is a known issue with the sirf chipsets, then i'll probably
put a bandaid into my application and call it a day. but i'm also
happy to do more debugging/logging, or add instrumentation, if that
would be helpful.
paul
=----------------------
paul fox, address@hidden (arlington, ma, where it's 72.1 degrees)
- [gpsd-users] possible week rollover problem,
Paul Fox <=