[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

[Achim Kraus]

Sounds strange, but though I haven't (re-)tested that, I'm not sure, if the things have changed in nRF9151/mfw 2.0.2 . That stuff with the "sticky network rejection" is some of the "deep spec documented" features, which is hard to understand and close to impossible to test.

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

[Achim Kraus]

Mlgr said:

(the watchdog still rebooted the card after a few minutes)

That depends on how many "a few" are in numbers ;-).

Depending on the used bands and modes (LTE-M/NB-IoT) such a network search may take some more time. I usually start with 3 min and double that search time for each search after a quiet phase.

[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.