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Re: [gpsd-dev] PPS in 3.11

From: Eric S. Raymond
Subject: Re: [gpsd-dev] PPS in 3.11
Date: Tue, 26 Aug 2014 23:14:23 -0400
User-agent: Mutt/1.5.21 (2010-09-15)

Gary E. Miller <address@hidden>:
> Uh, oh.  I see Miroslav's patch broke some unstated assumptions.
> His patch used the CALCULATED time of the last NMEA timestamp
> (last_fixtime_real).  Not the RECEIVED time of the last NMEA
> timestamp (last_fixtime_clock).
> That introduces a race between PPS and NMEA time and breaks the 
> assumption that the PPS time is on the edge of the next second.
> I can also see how some misleading variable names and unneeded
> copying and renameing of variables is confusing things.
> For example 'drift' implies to me a delta or rate of some kind, like
> the drift of a boat.  Instead it is an exact benchmark point in time.
> I'm gonna have to noodle over it a bit, but it is clearly broken.

I see a short-cycle release in our future, then.

And if it's broken, it's not very.  I've been live-checking the
results on my GR-601-W and the observed offset has been stable to a
small number of milliseconds through the patch.  It's possible the
reason Miroslav's patch doesn't look busted is that for reasonable
hardware like the uBlox it actually isn't.

Rename whatever varuiables and structures you like.  That code is so
complex that removing barriers to comprehensiion has to be top
                <a href="";>Eric S. Raymond</a>

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