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Re: [gpsd-dev] GPSD's assumptions about time
From: |
Eric S. Raymond |
Subject: |
Re: [gpsd-dev] GPSD's assumptions about time |
Date: |
Tue, 26 Nov 2013 14:41:05 -0500 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Sanjeev Gupta <address@hidden>:
> > 1. Compile the GPS week of the build into the build
> >
> > The obvious place tp put this is in timebase.h. Not too expensive;
> > will typically cause extra work once per seven days. The benefit is that
> > we can compare received week to the compiled-in week and if the latter
> > is less know that a rollover has occurred.
> >
>
> Would you (ESR) update timebase.h, or would the build process?
>
> If former, this seems fragile, and I suggest this need not be done every
> week, only as a release item.
> If the latter, than how do we ensure the build machine has a good GPS?: :-)
The build process. And we *compute* the GPS week from NTP time. That's
trivial.
> > 2. Track gpsd's confidence in the GPS time it's seeing.
> >
> > This would increase when we see a leap-second offset or get GPZDA from
> > the device, decrease when we detect a rollover. Some devices that are
> > known to deliver high-quality time (notably u-blox GPSes) would peg the
> > confidence measure at a high level.
> >
>
> Till u-blox makes a really cheap GPS, that goofs up, but still speals
> u-blox-ese fluently.
That is why we pay attention to firmware versions.
Besides, I don't think u-blox is going to do that. Ever. The place is run by
Swiss-German engineers from the Zurich region, mostly former ETH faculty.
Certain implications follow - this is the heart country of the precision
timepiece, and these are people who by instinct consider quality compromises
to be approximately as odious as murdering a close relative.
(Distant kin of mine, by the way. I'm largely Zuricher Swiss myself from my
mother's side of the family. Precision engineering is in my blood. No joke.)
--
<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
- [gpsd-dev] GPSD's assumptions about time, Eric S. Raymond, 2013/11/26
- Re: [gpsd-dev] GPSD's assumptions about time, Sanjeev Gupta, 2013/11/26
- Re: [gpsd-dev] GPSD's assumptions about time, Eric S. Raymond, 2013/11/26
- Re: [gpsd-dev] GPSD's assumptions about time, Hal Murray, 2013/11/26
- Re: [gpsd-dev] GPSD's assumptions about time, Eric S. Raymond, 2013/11/26
- Re: [gpsd-dev] GPSD's assumptions about time, Hal Murray, 2013/11/26
- Re: [gpsd-dev] GPSD's assumptions about time, Eric S. Raymond, 2013/11/28
Re: [gpsd-dev] GPSD's assumptions about time, Hal Murray, 2013/11/28