Crash in modem firmware 1.3.6

[Joakim Andersson]

Hi. We have a custom board with an nrf1960, which we use to communicate with Azure IoT Hub over LTE-M.

We are updating from NCS 2.4.2 and modem firmware 1.3.4 to NCS 2.7.0 and modem firmware 1.3.6.
On these new versions we are seeing that the modem firmware occasionally crashes with the following information:

 <err> nrf_modem: Modem has crashed, reason 0x10, PC: 0x11af7e

There is not really any surrounding information to give any indication what caused this to happen.
It looks like there are still events generated from the modem, but it does not respond to any AT commands with anything other than returning NRF_EPERM.

command read (CESQ):
1319 [04:30:02.537,719] <err> radio: AT+CESQ error -1
event generated: (CEREG)
1320 [04:30:02.726,440] <err> lte_lc: Could not get registration status, error: -1

After this the modem does not respond to any AT commands, unless a nrf_modem_lib_shutdown and nrf_modem_lib_init is called.

What is this crash, and how can we prevent it from happening?

[Øyvind]

Hello, 

Are you able to reproduce the issue? Could you try with modem FW 1.3.7 as well? It should be fine to use with NCS v2.7.0. 

If this does not help, we will need a modem trace of the issue. 

Kind regards,
Øyvind

[Joakim Andersson]

We're running many boards in our test-setup and 2 boards experienced this issue, earliest after 40 hours of run-time.
So acquiring a modem trace at the moment could be difficult.

Could you give some hints about what the assert is, that way we could maybe manage to reproduce the issue more reliably.

In the meantime we will also try 1.3.7 and see if the issue occurs there as well.