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Re: [gpsd-dev] Parallel build broken?

From: Eric S. Raymond
Subject: Re: [gpsd-dev] Parallel build broken?
Date: Tue, 26 Nov 2013 04:34:12 -0500
User-agent: Mutt/1.5.21 (2010-09-15)

Gary E. Miller <address@hidden>:
> > How many GPS receivers supported by gpsd send time to the computer in
> > GPS time, rather than UTC?
> Pretty much everyone I have looked at on a cold start.  When they have
> DELTAtlf then they give you UTC, and worse they do not tell you which is
> which or when they switch.

Paul: It's actually worse than that.

Many binary-mode receivers don't ship UTC at all, ever. Or, if they do,
it's in a sentence that is broken or not reliably present (I'm looking
at you, SiRF!).  Instead they ship (GPS week, time-of-week) in the main
navigation solution message, and leap-second offset in a different one.

Only sometimes they *don't* ship that different one after power-up
until they have a new sample of the periodic sat transmission
containing leap second. Sometimes they do ship the leap-second offset
from NVRAM before that unless the ephemeris is stale or the device has
been cold-booted. This choice is usually vaguely documented or
entirely undocumented.

On the other hand, in fallback NMEA mode they just give you what looks like
UTC.  With no way for you to know what leap-second offset they're
using.  And a two-digit year, only, unless the device emits GPZDA.
                <a href="";>Eric S. Raymond</a>

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