FreeBSD Garmin 18x LVC receiver - precision -20

[Philippe Maechler]

Hi gpsd users

 

I’m running my own ntp server and will now install a gps receiver to let my server be more accurate

 

The receiver is directly connected to the COM1 port

 

This is the output when launching gpsd

 

# gpsd -D 3 -N -n -s 4800 -F /var/run/gpsd.sock /dev/cuau0

gpsd:INFO: launching (Version 3.20)

gpsd:INFO: listening on port 2947

gpsd:INFO: stashing device /dev/cuau0 at slot 0

gpsd:INFO: SER: opening GPS data source type 2 at '/dev/cuau0'

gpsd:INFO: SER: speed 4800, 8N1

gpsd:INFO: SER: speed 4800, 8O1

gpsd:INFO: SER: speed 4800, 8N1

gpsd:INFO: SER: speed 4800, 8N1

gpsd:INFO: SER: speed 4800, 8N1

gpsd:INFO: gpsd_activate(2): activated GPS (fd 7)

gpsd:INFO: KPPS:/dev/cuau0 RFC2783 path:/dev/cuau0, fd is 7

gpsd:INFO: KPPS:/dev/cuau0 pps_caps 0x1133

gpsd:INFO: KPPS:/dev/cuau0 have PPS_CANWAIT

gpsd:INFO: KPPS:/dev/cuau0 kernel PPS will be used

gpsd:INFO: PPS:/dev/cuau0 ntpshm_link_activate: 1

gpsd:INFO: device /dev/cuau0 activated

gpsd:INFO: running with effective group ID 0

gpsd:INFO: running with effective user ID 65534

gpsd:INFO: startup at 2020-10-16T10:05:07.000Z (1602842707)

gpsd:INFO: /dev/cuau0 identified as type NMEA0183, 0 sec @ 4800bps

gpsd:INFO: Sats used (0):

gpsd:INFO: PPS:/dev/cuau0 Assert hooks called clock:  1602842709.000176550 real:  1602842709.000000000: no fix

gpsd:INFO: PRN=  1 az=124.0 ael65.0 (0.350366, -0.236325, 0.906308)

gpsd:INFO: PRN=  3 az=298.0 ael77.0 (-0.198620, 0.105608, 0.974370)

gpsd:INFO: PRN=  9 az=208.0 ael6.0 (-0.466900, -0.878111, 0.104528)

gpsd:INFO: PRN= 11 az=156.0 ael32.0 (0.344932, -0.774730, 0.529919)

gpsd:INFO: PRN= 17 az=301.0 ael38.0 (-0.675457, 0.405856, 0.615661)

gpsd:INFO: PRN= 19 az=316.0 ael24.0 (-0.634602, 0.657150, 0.406737)

gpsd:INFO: PRN= 21 az=129.0 ael23.0 (0.715367, -0.579292, 0.390731)

gpsd:INFO: PRN= 22 az=56.0 ael73.0 (0.242387, 0.163492, 0.956305)

gpsd:INFO: PRN= 31 az=78.0 ael20.0 (0.919158, 0.195373, 0.342020)

gpsd:INFO: Sats used (9):

gpsd:WARN: unknown sentence: "$PGRMC1,1,1,1,,,,2,W,N*4C\x0d\x0a"

gpsd:WARN: unknown sentence: "$PGRMC1,1,1,1,,,,2,W,N,,,,1,2,2*7D\x0d\x0a"

gpsd:INFO: PPS:/dev/cuau0 Assert hooks called clock:  1602842710.000177345 real:  1602842710.000000000: no fix

gpsd:INFO: PPS:/dev/cuau0 Assert hooks called clock:  1602842711.000178108 real:  1602842711.000000000: accepted

gpsd:INFO: PRN=  1 az=124.0 ael65.0 (0.350366, -0.236325, 0.906308)

gpsd:INFO: PRN=  3 az=298.0 ael77.0 (-0.198620, 0.105608, 0.974370)

gpsd:INFO: PRN=  9 az=208.0 ael6.0 (-0.466900, -0.878111, 0.104528)

gpsd:INFO: PRN= 11 az=156.0 ael32.0 (0.344932, -0.774730, 0.529919)

gpsd:INFO: PRN= 17 az=301.0 ael38.0 (-0.675457, 0.405856, 0.615661)

gpsd:INFO: PRN= 19 az=316.0 ael24.0 (-0.634602, 0.657150, 0.406737)

gpsd:INFO: PRN= 21 az=129.0 ael23.0 (0.715367, -0.579292, 0.390731)

gpsd:INFO: PRN= 22 az=56.0 ael73.0 (0.242387, 0.163492, 0.956305)

gpsd:INFO: PRN= 31 az=78.0 ael20.0 (0.919158, 0.195373, 0.342020)

gpsd:INFO: Sats used (9):

gpsd:WARN: cycle-start detector failed.

 

When I connect to telnet and issue the WATCH command I get:

{"class":"TPV","device":"/dev/cuau0","status":2,"mode":3,"time":"2020-10-16T09:45:04.000Z","ept":0.005,"lat":47.395181667,"lon":8.635330000,"altHAE":482.800,"altMSL":436.000,"alt":436.000,"epx":1.937,"epy":1.997,"epv":4.025,"track":207.6000,"magtrack":209.4000,"magvar":1.8,"speed":0.000,"climb":0.050,"eps":3.35,"epc":7.83,"geoidSep":46.800,"eph":3.325,"sep":4.750}

{"class":"PPS","device":"/dev/cuau0","real_sec":1602841505,"real_nsec":0,"clock_sec":1602841505,"clock_nsec":56414,"precision":-20}

{"class":"SKY","device":"/dev/cuau0","xdop":0.52,"ydop":0.53,"vdop":1.00,"tdop":0.59,"hdop":0.70,"gdop":1.36,"pdop":1.20,"satellites":[{"PRN":1,"el":75.0,"az":110.0,"ss":33.0,"used":true,"gnssid":0,"svid":1},{"PRN":3,"el":70.0,"az":273.0,"ss":26.0,"used":true,"gnssid":0,"svid":3},{"PRN":4,"el":29.0,"az":190.0,"ss":29.0,"used":true,"gnssid":0,"svid":4},{"PRN":8,"el":8.0,"az":174.0,"ss":33.0,"used":true,"gnssid":0,"svid":8},{"PRN":11,"el":41.0,"az":155.0,"ss":35.0,"used":true,"gnssid":0,"svid":11},{"PRN":17,"el":33.0,"az":309.0,"ss":47.0,"used":true,"gnssid":0,"svid":17},{"PRN":19,"el":17.0,"az":321.0,"ss":35.0,"used":true,"gnssid":0,"svid":19},{"PRN":21,"el":31.0,"az":124.0,"ss":31.0,"used":true,"gnssid":0,"svid":21},{"PRN":22,"el":81.0,"az":33.0,"ss":32.0,"used":true,"gnssid":0,"svid":22},{"PRN":28,"el":8.0,"az":266.0,"ss":24.0,"used":true,"gnssid":0,"svid":28},{"PRN":31,"el":16.0,"az":87.0,"ss":41.0,"used":true,"gnssid":0,"svid":31},{"PRN":32,"el":18.0,"az":43.0,"ss":49.0,"used":true,"gnssid":0,"svid":32}]}

 

My interpretation is, that the receiver is connected to 9 satellites but still does not get an accurate time (“precision":-20)

 

All in all my ntp server does not get time data from PPS (?). ntpq tells me, that its not reachable. But I’ll get to this when I’m sure that gpsd is working

 

Any help or insight are appreciated

 

TIA

Philippe