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Re: [gpsd-dev] [PATCH] Corrects info regarding 13-bit week numbers.


From: Gary E. Miller
Subject: Re: [gpsd-dev] [PATCH] Corrects info regarding 13-bit week numbers.
Date: Fri, 15 Jul 2016 19:15:52 -0700

Yo Fred!

Thanks for this patch.  Seems like 'git am' properly stripped munged
subject header.  Applied and pushed.

Looking at the patch, I woulda swore I already applied that.  That probably
added to my confusion on your git merge.  Somewhere I have a git outta
sink with head.

I'll spend some time looking at the merge stuff to get a handle on that,
but I've got some more old patches to get to first.

On Fri, 15 Jul 2016 18:49:39 -0700
Fred Wright <address@hidden> wrote:

> Also updates the "GPS Date Calendar" link, as requested by that
> website.
> ---
>  www/hacking.html.in | 32 +++++++++++++++++---------------
>  1 file changed, 17 insertions(+), 15 deletions(-)
> 
> diff --git a/www/hacking.html.in b/www/hacking.html.in
> index 20a0d2e..53deac3 100644
> --- a/www/hacking.html.in
> +++ b/www/hacking.html.in
> @@ -1192,11 +1192,11 @@ and bite on various future dates. </p>
>  
>  <ol>
>    <li>The GPS radio format has a Y2K-style bug, the week counter
> -  rollover, which happens either every 1024 weeks (roughly 20 years)
> or
> -  every 8192 weeks (roughly 157 years), depending on whether your
> -  receiver can decode a 10-bit or 13-bit GPS week field. At time of
> -  writing the last 0 week was in 1999, the next 10-bit wraparound
> will
> -  be in 2019, and the next 13-bit wraparound will be in 2157.</li>
> +  rollover, which happens either every 1024 weeks (roughly 19.6
> years)
> +  or every 8192 weeks (roughly 157 years), depending on whether your
> +  receiver can decode a 10-bit or 13-bit GPS week field.  At the
> time of
> +  this writing the last 0 week was in 1999, the next 10-bit
> wraparound
> +  will be in 2019, and the next 13-bit wraparound will be in
> 2137.</li> 
>    <li>NMEA delivers only two-digit years.</li>
>  
> @@ -1216,20 +1216,22 @@ after a rollover.  This can have side
> effects:</p> have a recent ephemeris.</li>
>  </ol>
>  
> -<p>The public documentation is unclear, but it appears from a
> -reference in the Transmission Week Number section of IS-GPS-200
> -PIRN-002 that whether you can get 10 or 13 bits is a function of the
> -satellite firmware revision, with 13 bits in the Block IIF and later
> -birds (the first of these was launched in May 2010). Of course your
> -receiver firmware also has to know that the extra three bits are
> -present; at time of writing in late 2010 this capability is very rare
> -and unavailable on consumer-grade receivers.</p>
> +<p>The new 13-bit week number is only provided by the new "CNAV"
> data, +which in turn is (or will be) available only in newly added
> GPS signals. +Based on the carrier frequencies used, only the newest
> of the new +signals (L1C) will be available to common civilian
> receivers, even with +compatible hardware and firmware.  This signal
> is unavailable from +satellites earlier than Block III, which are
> currently (July 2016) not +expected to begin to launch earlier than
> September 2016.  Given that it +takes years to launch a full
> constellation of satellites, it's highly +unlikely that CNAV data
> with "operational" status will be available to +common civilian
> receivers in time for the April 2019 10-bit rollover.</p> 
>  <p>For these reasons, GPSD needs the host computer's system clock to
>  be accurate to within one second.</p>
>  
> -<p>When debugging time and date issues, you may find an
> -<a href="http://adn.agi.com/GNSSWeb/";>interactive GPS calendar</a>
> +<p>When debugging time and date issues, you may find an interactive
> +<a href="http://navigationservices.agi.com/GNSSWeb/";>GPS Date
> Calendar</a> useful.</p>
>  
>  <h2 id="hotplug">Hotplug interface problems</h2>




RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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