[NRF9151] Modem does not connect after SIM deactivate/reactivate

[Mlgr]

Hi,

I’m using the Thingy:91X board with the nRF9151 chip, modem firmware version 2.0.2, and SDK version 2.9.0.

We’re encountering a serious issue: the modem does not reconnect after the SIM has been deactivated and then reactivated.

I’ve tried:

• sys_reboot(SYS_REBOOT_COLD)

• Placing the modem offline (lte_lc_offline())

• Shutting down the modem library (nrf_modem_lib_shutdown())

• Forcing a hard reboot via the watchdog

None of these approaches has worked.

Do you have any suggestions for resolving this issue?

The only workaround so far (which isn’t acceptable) is to manually power the device off and on.

Regards,
Mathieu

[Achim Kraus]

Not sure, how you really tested that.

There may be two pitfalls:

- the reactivation of the SIM may take some time (in some cases more minutes, even longer, especially, if you deactivate and reactivate multiple times in just a few minutes)

- some rejection cause are treated "sticky" by the modem. That requires usually to wait some time or do a "lte_lc_power_off/lte_lc_normal" cycle (but I didn't retest that for a nRF9151)

So, let me propose, that you try to wait a minute or so after reactivate the SIM until you test to connect the modem again. If that results in rejected registrations, then try a "lte_lc_power_off/lte_lc_normal" cycle.

[Mlgr]

Hello Achim,

I let the card run for a few days, but it never reconnected to the network. However, I have a watchdog that reboots the card after “x” minutes without data. Should I disable it? Could it be causing a conflict with the modem in the new version?

I already tried the lte_lc_power_off/lte_lc_normal cycle, but it didn’t work (the watchdog still rebooted the card after a few minutes).

Best regards,
Mathieu

[Mlgr]

The watchdog reboots the card after 5 minutes.

On reboot, the app restarts by calling (after initializing other components) nrf_modem_lib_init, modem_info_rsrp_register, and lte_lc_connect_async.

[Achim Kraus]

Achim Kraus said:

I will check the SIM deactivation/activation using 1nce and a nRF9151-DK. Let's see, what I get.  

I've tested it twice using a 1nce SIM.

In the first test, I activated the SIM after a couple of seconds, but the modem didn't test all the available TAC in that time. So the modem was able to reconnect to (a new) network without power-off/normal.

In the second test, I've waited until all available TAC rejected the modem with 15, before a activated the SIM again. Here it required the power-off/normal cycle as I was used to in the past.

But no watchdog, reboot nor power switch off-on cycle was required to get the modem connected again.

nRF9151-DK, NCS 2.9.2, mfw 2.0.2, nRF9151 LACA A0A

[Achim Kraus]

If 5 minutes are OK depends on the bands, the modes and the available networks. If you want to ensure, that this isn't the cause, just use 15 minutes and see, if that changes.  

[Mlgr]

If I understand correctly, the calls to lte_lc_power_off and lte_lc_normal should work.

I’ll retry them and increase the watchdog timeout to give the modem enough time to reconnect without being reset during the process.

I’ll let you know the results.

[Achim Kraus]

Mlgr said:

If I understand correctly, the calls to lte_lc_power_off and lte_lc_normal should work.

Yes, that was my experience with the nRF9160/mfw1.3.7 and is now the same in the retest with the nRF9151/mfw2.0.2. 

Mlgr said:

I’ll retry them and increase the watchdog timeout to give the modem enough time to reconnect without being reset during the process.

It should be at least worth to be tested.

Mlgr said:

I’ll let you know the results.

I'm looking forward.

[Mlgr]

I tried retesting using the lte_lc_power_off / lte_lc_normal cycle on disconnection, but now my device doesn’t connect at all, it just hangs after the “Searching” event (the same thing happens when I deactivate/reactivate the SIM but this SIM was always activated).

I enabled tracing as described here: https://docs.nordicsemi.com/bundle/ncs-2.9.0/page/nrf/libraries/modem/nrf_modem_lib/nrf_modem_lib_trace.html, but all I get are these logs:

[00:00:01.526,733] <inf> modem_trace_backend: Modem_trace RTT backend channel 1  
[00:00:01.526,733] <inf> nrf_modem_lib_trace: Trace thread ready  
[00:00:01.534,637] <inf> nrf_modem_lib_trace: Trace level override: 2  
[00:00:01.782,501] <err> nrf_modem_lib_trace: trace_backend.write failed with err: -63  
…  
[00:00:08.544,372] <err> nrf_modem_lib_trace: trace_backend.write failed with err: -63  
[00:00:13.396,179] <inf> lte_monitor: Network: Searching

I haven’t changed anything in this software version, and it was working fine two weeks ago. I’m really lost.

[Achim Kraus]

Mlgr said:

I haven’t changed anything in this software version, and it was working fine two weeks ago. I’m really lost.

You added the power_off/normal cycle and the modem trace via RTT.

I would start removing both and retest. If you use versioning, that may be easier to checkout a last working version and retest that.

And then adding one change step by step and see, if both stops the device from working or just one.

----------------------------------------------------------------------------------------

I'm used to trace the mode via UART and sometimes use the FLASH to keep a the trace for a time span (and afterward write that to the UART).

I never tried the RTT interface for the modem trace before, but at least using a nRF9151-DK, NCS 2.9.2, Ubuntu doesn't work for me either. I enabled it via the snippet, it start to report quite a lot of "trace_backend.write failed with err: -63". But using

nrfjprog --reset && JLinkRTTLogger -Device NRF9151_XXCA -If SWD -Speed 50000  modemtracesrtt.bin

(see How to capture nrf9160 modem traces using RTT? ) 

only reports:

SEGGER J-Link RTT Logger
Compiled Mar  5 2025 14:51:21
(c) 2016-2017 SEGGER Microcontroller GmbH, www.segger.com
         Solutions for real time microcontroller applications

Default logfile path: /home/achim/.config/SEGGER

------------------------------------------------------------ 


------------------------------------------------------------ 
Connected to:
  SEGGER J-Link (unknown)
  S/N: 1051240195

Searching for RTT Control Block...OK.
3 up-channels found:
0: Terminal
1: 
2: 
Selected RTT Channel description: 
  Index: 1
  Name:  
  Size:  0 bytes.

Output file: modemtracesrtt.bin

Getting RTT data from target. Press any key to quit.
------------------------------------------------------------ 

Transfer rate: 0 Bytes/s Data written: 0 Bytes 0

Not sure, may be this requires someone from Nordic to retest the modem trace via RTT. 

[Mlgr]

Achim Kraus said:

You added the power_off/normal cycle and the modem trace via RTT.

I would start removing both and retest. If you use versioning, that may be easier to checkout a last working version and retest that.

And then adding one change step by step and see, if both stops the device from working or just one.

That’s the problem: I flashed the same software that worked two weeks ago, but now this board won’t connect, even though it connects fine on another board. I think we received a defective batch, I’ve already thrown away five or six boards.

The modem sends a “Searching” event and then does nothing. That’s why I tried enabling modem tracing. But when I read its output over UART the data appears garbled, even though my DTS settings (baud rate, pins, etc.) are correct and I’m using 1,000,000 baud / 8 data bits / 1 start bit / 1 stop bit / no parity. I don’t know why the output isn’t legible, so I’m switching to RTT instead.

I really don’t understand why I’m having modem issues; I’ve never seen this with the Thingy:91 and I haven’t changed anything in my code.

On startup I call:

1. nrf_modem_lib_init()

2. modem_info_init()

3. modem_info_rsrp_register()

4. lte_lc_connect_async()

On shutdown I call:

• lte_lc_offline()

I have another board running exactly the same software and it works fine (I’d rather not deactivate/reactivate its SIM because I need it for something else).

Am I doing something wrong in my initialization sequence?

[dejans]

Hi,

Can you show how you enable tracing over UART and RTT?
You can read more about modem tracing in the documentation.

Best regards,
Dejan