Re: [gpsd-users] [gpsd-dev] RFC - drop "tag" fields from the public interface

[Hal Murray]

address@hidden said:
> Time is collected at the same point in the cycle every time. What sentence
> that is varies by GPS type but is always the same sentence type for any one
> GPS.

> There's a cycle detector in the code that watches timestamped sentences
> (ignoring others) looking for where the stamp changes from T to T+1.  It
> then marks the sentence type just *before* the T+1 sentence as the
> end-of-cycle type.  Thereafter, reports (including time) are issued on
> end-of-cycle.

> The uBlox 4 LEA is a representative example.  Each cycle it ships $GPZDA,
> $GPRMC, $GPVTG, $GPGGA, $GPGSA, $GPGSV, $GPGLL. Timestamps occur in ZDA RMC
> GGA GLL; the timestamp is incremented on ZDA.

> In this case, gspd notices that the timestamp is incremented on ZDA, which
> comes after GLL.  GLL is marked as end of cycle, reports are issued on every
> GLL using info accumulated from  ZDA RMC GGA GLL, and GLL fills the tag
> field of the resulting TPV.

Thanks.

OK, if that's how it works, I agree that the tag isn't useful.

One quirk to consider.  I've seen some units that do something like send GSV 
every 5th second.

$GPRMC,074835.000,A,3726.0787,N,12212.2705,W,0.37,253.56,240814,,*1E
$GPGGA,074836.000,3726.0786,N,12212.2701,W,2,07,1.9,42.2,M,-25.7,M,1.8,0000*7D
$GPGSA,A,3,31,11,01,32,20,04,23,,,,,,3.5,1.9,3.0*3A
$GPRMC,074836.000,A,3726.0786,N,12212.2701,W,0.46,321.68,240814,,*17
$GPGGA,074837.000,3726.0789,N,12212.2698,W,2,06,2.0,42.9,M,-25.7,M,0.8,0000*73
$GPGSA,A,3,31,11,01,32,04,23,,,,,,,3.6,2.0,3.0*31
$GPRMC,074837.000,A,3726.0789,N,12212.2698,W,0.80,10.86,240814,,*23
$GPGGA,074838.000,3726.0793,N,12212.2694,W,2,06,2.0,43.3,M,-25.7,M,1.8,0000*71
$GPGSA,A,3,31,11,01,32,04,23,,,,,,,3.6,2.0,3.0*31
$GPRMC,074838.000,A,3726.0793,N,12212.2694,W,0.55,359.72,240814,,*16
$GPGGA,074839.000,3726.0799,N,12212.2699,W,2,07,1.9,44.7,M,-25.7,M,2.8,0000*7C
$GPGSA,A,3,31,11,01,32,20,04,23,,,,,,3.5,1.9,3.0*3A
$GPRMC,074839.000,A,3726.0799,N,12212.2699,W,1.10,10.08,240814,,*23
$GPGGA,074840.000,3726.0801,N,12212.2696,W,2,07,1.9,44.6,M,-25.7,M,0.8,0000*70
$GPGSA,A,3,31,11,01,32,20,04,23,,,,,,3.5,1.9,3.0*3A
$GPGSV,3,1,12,32,71,348,28,31,64,090,22,01,54,273,27,11,39,235,22*7E
$GPGSV,3,2,12,20,31,307,18,04,23,312,29,14,22,056,,23,19,258,23*79
$GPGSV,3,3,12,22,14,114,,25,08,052,,17,01,315,,48,45,197,28*7B


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