[gpsd-dev] Off by a second

[Hal Murray]

Are you interested in chasing this?

I've got a setup with GPS+PPS over USB.  It's a Sparkfun "Venus GPS" 
connected via a Sparkfun "FT232R breakout" and 5 wires.  The Venus has a 
SkyTrak 638 chip.

ntpq -p shows:

     remote           refid      st t when poll reach   delay   offset  jitter
 SHM(0)          .SHM.            0 l   42   64    7    0.000 -631.653  17.853
 SHM(1)          .SHM.            0 l   41   64    7    0.000 -1000.60   0.166
 GPSD_JSON(0)    .GPSD.           0 l   41   64    3    0.000 -562.875 242.126
 GPSD_JSON(128)  .GPSD.           0 l   40   64    3    0.000 -1000.59   0.010
(The clock on that box is accurate.)

The TOFF slot in gpsmon alternates between 0.2 and 0.6.  It switches to 0.2 
as stuff starts scrolling by.  It switches back to 0.6 at the end.  (within 
my eye accuracy)  I see GPGGA at the start and GPRMC near the end, so that 
seems reasonable.

The PPS is solid at 1.000

from gpsmon's log

------------------------------------- PPS ------------------------------------
-
$GPGGA,082228.809,3726.0952,N,12212.2454,W,1,07,1.3,32.3,M,-32.2,M,,0000*5F^M
$GPGSA,A,3,14,27,04,18,19,32,22,,,,,,2.5,1.3,2.2*33^M
$GPGSV,3,1,12,14,79,055,27,22,59,056,38,04,40,311,33,19,39,256,27*77^M
$GPGSV,3,2,12,32,29,285,22,27,27,221,14,18,27,081,23,11,26,309,00*70^M
$GPGSV,3,3,12,31,17,166,,01,14,316,00,24,11,040,00,21,04,138,*70^M
$GPRMC,082228.809,A,3726.0952,N,12212.2454,W,000.0,191.0,010715,,,A*7F^M
$GPVTG,191.0,T,,M,000.0,N,000.0,K,A*04^M
------------------------------------- PPS ------------------------------------
-
$GPGGA,082229.809,3726.0952,N,12212.2454,W,1,07,1.3,32.3,M,-32.2,M,,0000*5E^M
$GPGSA,A,3,14,27,04,18,19,32,22,,,,,,2.5,1.3,2.2*33^M
$GPGSV,3,1,12,14,79,055,27,22,59,056,38,04,40,311,33,19,39,256,27*77^M
$GPGSV,3,2,12,32,29,285,22,18,27,081,23,27,27,221,14,11,26,309,00*70^M
$GPGSV,3,3,12,31,17,166,,01,14,316,,24,11,040,00,21,04,138,*70^M
$GPRMC,082229.809,A,3726.0952,N,12212.2454,W,000.0,191.0,010715,,,A*7E^M
$GPVTG,191.0,T,,M,000.0,N,000.0,K,A*04^M
------------------------------------- PPS ------------------------------------
-

I'll get timings on the individual sentences if you want.

Looks like the PPS is 5 ms wide.

address@hidden murray]# cat /sys/devices/virtual/pps/pps1/assert
1435740091.004800422#271
address@hidden murray]# cat /sys/devices/virtual/pps/pps1/assert
1435740093.004880354#273
address@hidden murray]# cat /sys/devices/virtual/pps/pps1/assert
1435740094.004927374#274
address@hidden murray]# cat /sys/devices/virtual/pps/pps1/clear 
1435740098.000110354#278
address@hidden murray]# cat /sys/devices/virtual/pps/pps1/clear 
1435740099.000162683#279
address@hidden murray]# 


-- 
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