EM7590 not sending NMEA sentences

IoT Modules MC/EM Series
1

Hello,I’m currently having issues with a EM7590 module and how the GPS works on it. This module is attached a Syslogic Nvidia Jetson device running a balena OS.

Very occasionally (Approximately once every 20 or so cold boots) the GPS would work fine and we would get a constant stream of NMEA strings from the NMEA port on /dev/ttyUSB1.

However, most of the time we would get no NMEA data at all from the port but in this state, it will occasionally send a stream of 10 or so messages before stopping again. This is usually the message stream it sends to us before stopping again.

$GPGGA,0,66
$GPVTG,T,M,N,K,N2C
$GPRMC,V,N53
$GPGSA,A,1,32
$GPGGA,0,66
$GPVTG,T,M,N,K,N2C
$GPRMC,V,N53
$GPGSA,A,1,32
$GLGSV,1,1,02,38,39,17B
$GPGSV,1,1,01,25,35,164
$GPGGA,0,66
$GPVTG,T,M,N,K,N2C
$GPRMC,V,N*53
$GPGSA,A,1,*32

The following is the configuration for the modem

AT
OK

ati3
Manufacturer: Sierra Wireless
Model: EM7590
Revision: SWIX12C_02.02.03.00 2024/01/29 23:36:42
SVN: 05
IMEI: 357999720312919
FSN: DX5036002105H1
TS.25: 2024.1.1
+GCAP: +CGSM

OK

AT!GNSSCONFIG?
GPS: 1
GLONASS: 1
BDS: 1
GAL: 1
QZSS: 1

OK
AT!GPSAUTOSTART?
function: 2
fixtype: 2
maxtime: 254 seconds
nmaxdist: 50 meters
fixrate: 1 seconds

OK
AT!GPSCONF?
0,1,“”,4

OK
AT!GPSLOC?
Not Available

OK
AT!GPSNMEACONFIG?
Enabled: 1
Output Rate: 1

OK
AT!GPSNMEASENTENCE?
!GPSNMEASENTENCE: 5F

OK
AT!GPSSATINFO?
NO SAT INFO

OK
AT!GPSSTATUS?
2025 08 14 3 04:50:01 Last Fix Status = FAIL, FAILCODE = 4
2025 08 14 3 04:50:02 Fix Session Status = ACTIVE

No TTFF available

OK
AT!GPSSUPLURL?
supl.google.com

OK
AT!GPSSUPLVER?
!GPSSUPLVER: 2

OK
AT+WANT?
Preferred: 1
Current: 0

OK
AT!CUSTOM?
!CUSTOM:
“SIMLPA” 0x01
“UIM2ENABLE” 0x01
“GPSENABLE” 0x01
“MBIMTYPE” 0x01

OK

We do send $GPS_START to the GPS AT port when we first start the device but that doesn’t seem to change this behavior (Sent it both as a echo to the ttyUSB1 port and sent it over minicom, also tried it with $GPS_START/r and $GPS_START/r/n)

We assume it’s a config/software issue because we see this issue on all our current devices with the EM7590 modules (approximately 30+ units)

2

how about using latest firmware?

https://source.sierrawireless.com/resources/airprime/minicard/75xx/em7590/em7590-approved-fw-packages/#sthash.QuzdpHaC.dpbs

3

Unfortunately we have these devices out in the field and we aren’t in a position where we can easily update the firmware on them.

Is there something else we can try to at least verify it is a firmware issue or an issue with how we are configuring the module?

4

I tried the same firmware 02.02.03.00 as yours in EM7590, I can see the NMEA frame.

$GPGGA,0,66
$GPVTG,T,M,N,K,N2C
$GPRMC,V,N*53
$GPGSA,A,1,32
$GPGGA,0,66
$GPVTG,T,M,N,K,N2C
$GPRMC,V,N53
$GPGSA,A,1,*32

5

So we also do get NMEA messages occasionally. The issue is that it seems to just stop after a couple of seconds.

Having looked into it further we are noticing a couple things

  1. From a cold boot, for the first 30 seconds or so, if we send !GPSSTATUS we would get Last Fix Status = None. At this point, if we are observing the NMEA port, we would see those no fix NMEA messages I mentioned in the first post
  2. After 30 seconds, if we send !GPSSTATUS again, we would now get Last Fix Status = Fail, FailCode=4 which we understand to be GPS fix timeout (We would assume it would follow the max time param in our auto start config, which is 50 seconds but it doesn’t). The moment it switched to Fail, we would stop getting NMEA messages
  3. From this point onwards, the modem will stay on this Last Fix Status = Fail state.

We then tried to force it to get a fix by send !GPSFIX=1,255,1. Sometimes this message will return a ERROR message (But doesn’t return a error code like EM759x AT Reference Manual seems to suggest) but retrying the message a few times eventually returns a OK code.

Once that happens, Last Fix Status would be SUCCESS and we would start seeing NMEA messages again and it will keep sending NMEA messages until it goes back to Last Fix Status is FAIL. Not sure what causes it to go from SUCCESS to FAIL thou because just outright removing the antenna doesn’t seem to cause that, it would just stay on SUCCESS and keep resending the last good position, but we have definitely seen the modem go from SUCCESS to FAIL, which subsequently stops the NMEA messages.

So I guess our question at this point is

  1. Is the modem supposed to stop sending NMEA messages if Last Fix Status is Failed
  2. Is there a reason why the modem doesn’t seem to retry getting a fix automatically until we manually send a !GPSFIX message despite !GPSAUTOSTART being set
Sierra Wireless EM7590 – GNSS Enabled but No Fix / No Satellite Info
6

Can it be fixed after

At!gpsend=0

At!gpsfix=1,255,10000

7

!GPSEND will always send an ERROR back and like I mentioned above, sending !GPSFIX does make it work for a bit but it would also just stop sending NMEA strings, coinciding with it going into the FAIL last fix state with failcode 4.

Even sending !GPSFIX is not always guaranteed since 6/10 times, it will return ERROR with no error code

8

i cannot see such issue:

at!entercnd=“A710”
OK
at!gpsend=0
OK
at!gpsfix=1,255,100000

OK
ati3
Manufacturer: Sierra Wireless
Model: EM7590
Revision: SWIX12C_02.02.03.00 2024/01/29 23:36:42
SVN: 05
IMEI: 357999720012345
FSN: 01225200012345
TS.25: 2024.1.1
+GCAP: +CGSM

OK
at!gpsend=0
OK
at!gpsfix=1,255,100000

OK
at!gpsend=0
OK
at!gpsfix=1,255,100000

OK
at!gpsend=0
OK
at!gpsfix=1,255,100000

OK
at!gpsend=0
OK
at!gpsfix=1,255,100000

OK
at!gpsend=0
OK
at!gpsfix=1,255,100000

OK

9

Hello,

Just as an update, we’ve had a chance to bring up one of our client devices locally in our office so that we can update the firmware

We are now using the latest generic firmware
ATI
Manufacturer: Sierra Wireless
Model: EM7590
Revision: SWIX12C_03.01.02.00 2025/04/25 14:37:44
SVN: 07
IMEI: 357999720312919
FSN: DX5036002105H1
TS.25: 2025.2.24
+GCAP: +CGSM

We are noticing a couple things

  • The ttyUSB paths seem to have suddenly changed and is now showing as ttyUSB0, ttyUSB2 and ttyUSB3. (USB2 being NMEA and USB3 being AT)
  • With the exact same configuration as specified in my first post, the modem is returning ZERO NMEA sentences. It will rarely send a $PSTIS, *61 message but nothing else (Even if we send a GPSFIX or GPSTRACK message)
  • The modem will return an OK for !GPSEND and !GPSFIX, which causes the last fix session to go from FAIL to NONE back to FAIL in the span of a couple seconds.

Does your test devices show constant NMEA sentences?

10

did you go outdoor area to test?