LTE Link Monitor Issue with 9160

[Benjamin]

I was starting to develop for our own board based on the nRF9160 where we will just be using the LTE-M and while doing so, ran into issues with enabling the LTE. To do a sanity check, I went back to the 'at_client' example in the nRF Connect SDK 2.0.2 and programmed it on. I opened up the LTE Link Monitor v2.0.1 and this is what I'm seeing -- all the status indicators are red or gray:

I was able to get the Modem and UICC to turn green *once* by pulling out the SIM card and putting it back in, but then restarted the board and everything is red again. Here is my log file contents:

2022-08-01T21:44:31.667Z DEBUG Application data folder: /Users/user/Library/Application Support/nrfconnect/pc-nrfconnect-linkmonitor
2022-08-01T21:44:32.762Z INFO Using nrf-device-lib-js version: 0.4.11
2022-08-01T21:44:32.762Z INFO Using nrf-device-lib version: 0.11.8
2022-08-01T21:44:32.763Z INFO Using nrfjprog DLL version: 10.15.4
2022-08-01T21:44:32.763Z INFO Using JLink version: JLink_V7.64e
2022-08-01T21:44:32.895Z DEBUG App pc-nrfconnect-linkmonitor v2.0.1 official
2022-08-01T21:44:32.895Z DEBUG App path: /Users/user/.nrfconnect-apps/node_modules/pc-nrfconnect-linkmonitor
2022-08-01T21:44:32.895Z DEBUG nRFConnect 3.11.1, required by the app is (^3.8.0)
2022-08-01T21:44:32.895Z DEBUG nRFConnect path: /Applications/nRF Connect for Desktop.app/Contents/Resources/app.asar
2022-08-01T21:44:32.895Z DEBUG HomeDir: /Users/user
2022-08-01T21:44:32.895Z DEBUG TmpDir: /var/folders/0l/h7c0fmrn2s99zfj4sb1qlk_r0000gn/T/
2022-08-01T21:44:32.913Z INFO Installed JLink version does not match the provided version (V7.58b)
2022-08-01T21:44:35.732Z INFO Modem port is opened
2022-08-01T21:44:35.759Z DEBUG modem >> AT+CFUN?
2022-08-01T21:44:35.801Z DEBUG modem << +CFUN: 0
2022-08-01T21:44:35.804Z DEBUG modem << OK
2022-08-01T21:44:40.573Z DEBUG modem >> AT
2022-08-01T21:44:40.585Z DEBUG modem << OK
2022-08-01T21:44:51.655Z DEBUG modem << *** Booting Zephyr OS build v3.0.99-ncs1-1  ***
2022-08-01T21:44:51.676Z DEBUG modem << The AT host sample started
2022-08-01T21:45:13.078Z DEBUG modem >> AT+CFUN?
2022-08-01T21:45:13.088Z DEBUG modem << +CFUN: 0
2022-08-01T21:45:13.125Z DEBUG modem << OK
2022-08-01T21:45:14.661Z DEBUG modem >> AT+CFUN=1
2022-08-01T21:45:14.705Z DEBUG modem << OK
2022-08-01T21:45:48.294Z DEBUG modem >> AT+COPS=?
2022-08-01T21:48:48.295Z ERROR Network search failed: Error: 'AT+COPS=?
' timed out

What could possibly be going wrong here? I thought I was just configuring our new project incorrectly, but now using the 'at_client' example I get the same behavior. 

[SoTXhelp]

Hello Benjamin,

In the Systemmode command you can instruct the modem that You want to have a primary selection of Cat M1, you could enable or disable GNSS as an option and lastly you can tell the instuction that you only want Cat M1 Mode or have the option to search both networks.

If you will only be in M1 then I suggest 

AT%SYSTEMMODE=1,0,0,1

As Charlie points out, The clue was the CEREG with the indication of NB selected "9".

Helping decipher what we see in the log that aids in the diagnostic for us. 

< +CEREG: 2,"F1D4","016186CB",9,0,11

We see the still searching "2", "TAC"=0xF1D4, "CellID"= 0x016186 CB, "9" = NB,"0",EMM Error code "11" Cause #11 – PLMN not allowed

Tmobile Network PLMN = 310260

Cellmapper Tmobile Tower Location

  

< %CESQ: 36,1,20,2 - Signal quality -104

< %CESQ: 255,0,255,0 - Switching tower reselection: indicated by no signal

 

< %CESQ: 47,2,11,1

New tower selected

< +CEREG: 2,"9C14","06E9E03B",9

We are still searching for the network "2", Tracking Area "0x9C14", CellID 0x06E9E0 3B

ATT PLMN 310410

Cellmapper AT&T Tower Location

< +CNEC_EMM: 15 - We are receiving an EMM Error "15" Cause #15 – No suitable cells in tracking area

< +CEREG: 2,"9C14","06E9E03B",9,0,15

Repeat from above with additional EMM 15 error (No Suitable cells in tracking area.

 

< %CESQ: 255,0,255,0

Reselection Still searching

< +CEREG: 2

 

< +CEREG: 2,"0D92","0034571E",9

New Network, Tracking Area "0x0D92", CellID 0x003457 1E

Verizon PLMN 311480

 

Cellmapper Verizon Tower Location Link

 

< +CNEC_ESM: 32,0

ESM Error 32 = Cause #32 – Service option not supported

< +CNEC_EMM: 19

EMM Error 19 = Cause #19 – ESM failure

< +CEREG: 2,"0D92","0034571E",9,0,19

< +CEREG: 2

[Benjamin]

Ok, when I use those commands, it works! However, when I rebuild and reflash, it doesn't work again. I went through my kconfig for the nrf91 modem and it seems to be the same *except* I have the "nRF91 LTE Link control library" enabled on my own build. I have the LTE-M selected as my network mode, but it just keeps pulsing that it's searching, but if I run the commands you mentioned:

AT+CFUN=4
AT%XSYSTEMMODE=1,0,0,0
AT+CFUN=1

Then it works fine. What would I have wrong in the kconfig? That seems to be where my issue is, but I can't quite spot it.

[Charlie]

Hi Benjamin,

The AT client sample does not use functions from the nRF91 LTE Link control library. As I mentioned, you need to manually send commands. Even the LTE Link Monitor Automatic requests options do is just help you send check commands. We have many nRF9160 samples to demo how to use LTE link controller, the simplest one is the UDP sample if you want to learn how to use it, please pay attend to the connect_to_lte and lte_handler functions.

Best regards,

Charlie

[Benjamin]

Thank you! That helped me figure things out.