Re: [gpsd-dev] [PATCH] Update documentation on the 2019 GPS week rollover

[Gary E. Miller]

Yo Sanjeev!

Pushed to git head.  Thanks!

On Tue, 28 May 2019 02:31:44 +0800
Sanjeev Gupta <address@hidden> wrote:

> Also pulled in Gary's commit 41141c03a into NMEA.adoc
> ---
>  www/NMEA.adoc                    | 18 +++++++++++++++---
>  www/gpsd-time-service-howto.adoc |  7 ++++---
>  www/hacking.html.in              |  6 +++---
>  3 files changed, 22 insertions(+), 9 deletions(-)
> 
> diff --git a/www/NMEA.adoc b/www/NMEA.adoc
> index eb10cdd4..f3594fd2 100644
> --- a/www/NMEA.adoc
> +++ b/www/NMEA.adoc
> @@ -210,12 +210,13 @@ second and the following subframe broadcast.
>  
>  GPS date and time are subject to a rollover problem in the 10-bit
> week number counter, which will re-zero every 1024 weeks (roughly
> every 19.6 -years). The last rollover (and the first since GPS went
> live in 1980) -was in Aug-1999; the next will fall in Apr-2019.  The
> new "CNAV" data +years). The first rollover since GPS went live in
> 1980 was in Aug-1999, +followed by Apr-2019, the next will be in
> Nov-2038 (the 32-bit and POSIX +issues will probably be more
> important by then).  The new "CNAV" data format extends the week
> number to 13 bits, with the first rollover occurring in Jan-2137, but
> this is only used with some newly added GPS signals, and is unlikely
> to be usable in most consumer-grade receivers -prior to the 2019
> rollover. +currently.
>  
>  For accurate time reporting, therefore, a GPS requires a supplemental
>  time references sufficient to identify the current rollover period,
> @@ -1241,6 +1242,17 @@ Field Number:
>  
>  Example: $GNGSA,A,3,80,71,73,79,69,,,,,,,,1.83,1.09,1.47*17
>  
> +Note: NMEA 4.1+ systems (in particular u-blox 9) emit an extra field
> +just before the checksum.
> +
> +-----------------------------------------------
> +1 = GPS L1C/A, L2CL, L2CM
> +2 = GLONASS L1 OF, L2 OF
> +3 = Galileo E1C, E1B, E5 bl, E5 bQ
> +4 = BeiDou B1I D1, B1I D2, B2I D1, B2I D12
> +-----------------------------------------------
> +
> +
>  === GSV - Satellites in view ===
>  
>  This is one of the sentences commonly emitted by GPS units.
> diff --git a/www/gpsd-time-service-howto.adoc
> b/www/gpsd-time-service-howto.adoc index 3bee4720..c4ae7553 100644
> --- a/www/gpsd-time-service-howto.adoc
> +++ b/www/gpsd-time-service-howto.adoc
> @@ -137,12 +137,13 @@ second and the following subframe broadcast.
>  
>  GPS date and time are subject to a rollover problem in the 10-bit
> week number counter, which will re-zero every 1024 weeks (roughly
> every 19.6 -years). The last rollover (and the first since GPS went
> live in 1980) -was in Aug-1999; the next will fall in Apr-2019.  The
> new "CNAV" data +years). The first rollover since GPS went live in
> 1980 was in Aug-1999, +followed by Apr-2019, the next will be in
> Nov-2038 (the 32-bit and POSIX +issues will probably be more
> important by then).  The new "CNAV" data format extends the week
> number to 13 bits, with the first rollover occurring in Jan-2137, but
> this is only used with some newly added GPS signals, and is unlikely
> to be usable in most consumer-grade receivers -prior to the 2019
> rollover. +currently.
>  
>  For accurate time reporting, therefore, a GPS requires a supplemental
>  time references sufficient to identify the current rollover period,
> diff --git a/www/hacking.html.in b/www/hacking.html.in
> index df9ddcb8..d7b870e6 100644
> --- a/www/hacking.html.in
> +++ b/www/hacking.html.in
> @@ -1211,8 +1211,8 @@ and bite on various future dates. </p>
>    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>
> +  this writing the last 0 week was in 2019, the next 10-bit
> wraparound
> +  will be in 2038, and the next 13-bit wraparound will be in
> 2137.</li> 
>    <li>NMEA delivers only two-digit years.</li>
>  
> @@ -1241,7 +1241,7 @@ 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> +common civilian
> receivers for some years yet.</p> 
>  <p>For these reasons, GPSD needs the host computer's system clock to
>  be accurate to within one second.</p>




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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