GPS NMEA port stops responding after 3 minutes

Hi,
I am running an EM7455 on an embedded linux system and I am able to connect to the GPS using /dev/ttyUSB1. I echo $GPS_START to the port and I see NMEA messages, but after 3 minutes the messages stop, even while the GPS continues to run and attach to satellites and update the location?

For the NMEA port:
$ echo $GPS_START > /dev/ttyUSB1
$ cat < /dev/ttyUSB1
$GPVTG,T,M,N,K,N*2C

$GPGSA,A,1,*1E

$GPGGA,0,*66

$GPRMC,V,N*53

After 3 minutes the output stops.

on /dev/ttyUSB2:
AT+WANT=1 //Enable the GPS active antenna
AT!GPSSTATUS?
Current time: 1980 01 06 6 00:02:58

1980 01 06 6 00:02:58 Last Fix Status = NONE
1980 01 06 6 00:00:18 Fix Session Status = ACTIVE

No TTFF available

OK
AT!GPSSATINFO?
Satellites in view: 13 (1980 01 06 6 00:05:54)

  • SV: 1 ELEV: 9 AZI: 317 SNR: 18
  • SV: 8 ELEV: 27 AZI: 264 SNR: 29
  • SV: 10 ELEV: 50 AZI: 54 SNR: 21
  • SV: 11 ELEV: 20 AZI: 310 SNR: 26
  • SV: 14 ELEV: 73 AZI: 246 SNR: 23
  • SV: 18 ELEV: 28 AZI: 81 SNR: 33
  • SV: 21 ELEV: 11 AZI: 142 SNR: 19
  • SV: 22 ELEV: 6 AZI: 286 SNR: 23
  • SV: 24 ELEV: 7 AZI: 37 SNR: 22
  • SV: 27 ELEV: 24 AZI: 223 SNR: 19
  • SV: 31 ELEV: 21 AZI: 170 SNR: 29
  • SV: 32 ELEV: 79 AZI: 352 SNR: 23
  • SV: 48 ELEV: 0 AZI: 0 SNR: 35

OK
AT!GPSSTATUS?
Current time: 1980 01 06 6 00:06:09

1980 01 06 6 00:06:09 Last Fix Status = SUCCESS
1980 01 06 6 00:06:09 Fix Session Status = ACTIVE

TTFF (sec) = 203

OK
AT!CUSTOM?
!CUSTOM:
GPSENABLE 0x01
GPSSEL 0x01
SIMLPM 0x01
USBSERIALENABLE 0x01
FASTENUMEN 0x01
SINGLEAPNSWITCH 0x01

OK
AT+GMR
SWI9X30C_02.08.02.00 r5428 CARMD-EV-FRMWR2 2016/01/06 20:38:53

OK

Any ideas why this would happen, or how I can recover from it?

Thanks,
Adam

Adam,

I would suggest the first thing to do is upgrade the firmware, 2.08 is 2 years old now and there have been a lot of changes/improvements in the firmware.

Regards

Matt

Hi Adam,

The SNRs seem to be quite low. I wonder if it could cause problems in this case.

Br, Karppa

Thanks Matt, I have upgraded the firmware (took a little bit of doing, hence my late response), but I am seeing the same behavior:

AT+GMR
SWI9X30C_02.24.05.06 r7040 CARMD-EV-FRMWR2 2017/05/19 06:23:09

OK

AT!GPSSTATUS?
Current time: 2017 11 01 2 16:14:37

2017 11 01 2 16:14:37 Last Fix Status = SUCCESS
2017 11 01 2 16:14:37 Fix Session Status = ACTIVE

TTFF (sec) = 102

OK

(But nmea port stops after 3 minutes of messages)

Hi Karppa, I am indoors so the signal strength is relatively low, but I see the same behavior when I am near a window and the signals are stronger

While the messages are streaming I can start and stop with $GPS_START and $GPS_STOP, but after 3 minutes I don’t see output even when I try to restart the interface with the commands.

Thanks,
Adam

Adam,

I reckon your issue is the autostart max time parameter.

at!gpsautostart?
  function:  2
  fixtype: 1
  maxtime: 180 seconds
  maxdist: 50 meters
  fixrate: 1 seconds

OK

If it does not have a fix within 3 minutes by default it stops.

Regards

Matt

Hmmm… good thought I tried changing this to 30 seconds and power cycling the modem but the port still stops after 3 minutes

at!gpsautostart?
  function:  2
  fixtype: 1
  maxtime: 30 seconds
  maxdist: 50 meters
  fixrate: 1 seconds

OK

The weird thing is that the location is being still being updated through the AT query, so I don’t think the fix is timing out

at!gpsloc?
Lat: XX Deg XX Min 7.73 Sec N  (0xXXXXXXXX)
Lon: XXX Deg XX Min 31.22 Sec W  (0xXXXXXXXX)
Time: 2017 11 01 2 17:44:11 (GPS)
LocUncAngle: 0.0 deg  LocUncA: 7 m  LocUncP: 6 m  HEPE: 9.219 m
3D Fix
Altitude: 114 m  LocUncVe: 8.0 m
Heading: 0.0 deg  VelHoriz: 0.0 m/s  VelVert: 0.0 m/s