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author | Gary E. Miller <gem@rellim.com> | 2019-05-27 15:03:32 -0700 |
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committer | Gary E. Miller <gem@rellim.com> | 2019-05-27 15:03:32 -0700 |
commit | 6de94e9274c0ccd76927b5043fe159dc269b0aa1 (patch) | |
tree | d7af27aaeb03b5f633de8d6eb91b557d0e3af0f0 | |
parent | 4bc6a54b1f337674777181b80026e992b47ca4cd (diff) | |
parent | 0402eb81691882b4d693f9009f1f7369b205fa1d (diff) | |
download | gpsd-6de94e9274c0ccd76927b5043fe159dc269b0aa1.tar.gz |
Merge branch 'master' of ssh://git.sv.gnu.org/srv/git/gpsd
-rw-r--r-- | www/NMEA.adoc | 18 | ||||
-rw-r--r-- | www/gpsd-time-service-howto.adoc | 7 | ||||
-rw-r--r-- | 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> |