Update documentation on the 2019 GPS week rollover

Also pulled in Gary's commit 41141c03a into NMEA.adoc

Signed-off-by: Gary E. Miller <gem@rellim.com>

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>