Modem connection issues after reboots

[Paul Kajdewicz]

Hey

We encounter problems with the modem not establishing a connection after rebooting the processor for a few times.

Issue:

• Firmware is booting normally
• Cellular connection is established
• Device reboots after a minute via 

  sys_reboot(SYS_REBOOT_COLD);

  (normal behaviour, because cloud does not deliver relevant data)
• [reboots happen four times]
• after the fourth restart, the modem does not establish a cellular connection anymore

Way to reproduce

• Get any firmware running. You need to have access to the shell + kernel shell + lte_lc DBG LOGs
• restart your device via shell a few times with kernel reboot cold

LOGs:

normal behaviour
[00:00:06.766,723] <dbg> lte_lc.at_handler: +CEREG notification: +CEREG: 2,"AF9C","00AA6A65",9 [00:00:06.766,937] <inf> cloud: CIOT_NETWORK_CONNECTING [00:00:06.766,937] <wrn> ct: New cell id: 0x00aa6a65 [00:00:06.766,937] <wrn> ct: New tracking area code: 0xaf9c [00:00:06.766,967] <dbg> at_notif.notif_dispatch: Done [00:00:06.766,967] <dbg> at_cmd.socket_thread_fn: Writing any pending command [00:00:06.766,998] <dbg> at_cmd.socket_thread_fn: Listening on socket [00:00:07.408,905] <dbg> at_cmd.socket_thread_fn: at_cmd_rx 12 bytes, +CSCON: 1 [00:00:07.408,935] <dbg> at_notif.notif_dispatch: Dispatching events: [00:00:07.408,935] <dbg> at_notif.notif_dispatch: - ctx=0x00000000, handler=0x00032E5D [00:00:07.408,966] <dbg> at_notif.notif_dispatch: - ctx=0x00000000, handler=0x0001D511 [00:00:07.408,966] <dbg> lte_lc.at_handler: +CSCON notification [00:00:07.409,057] <dbg> at_notif.notif_dispatch: Done [00:00:07.409,088] <dbg> at_cmd.socket_thread_fn: Writing any pending command [00:00:07.409,088] <dbg> at_cmd.socket_thread_fn: Listening on socket [00:00:09.013,793] <dbg> at_cmd.socket_thread_fn: at_cmd_rx 18 bytes, +CNEC_ESM: 50,0 [00:00:09.013,824] <dbg> at_notif.notif_dispatch: Dispatching events: [00:00:09.013,824] <dbg> at_notif.notif_dispatch: - ctx=0x00000000, handler=0x00032E5D [00:00:09.013,824] <wrn> ct: AT notification received: +CNEC_ESM: 50,0 [00:00:09.013,824] <dbg> at_notif.notif_dispatch: - ctx=0x00000000, handler=0x0001D511 [00:00:09.013,885] <dbg> at_notif.notif_dispatch: Done [00:00:09.013,916] <dbg> at_cmd.socket_thread_fn: Writing any pending command [00:00:09.013,946] <dbg> at_cmd.socket_thread_fn: Listening on socket [00:00:09.013,977] <dbg> at_cmd.socket_thread_fn: at_cmd_rx 56 bytes, +CEREG: 5,"AF9C","00AA6A65",9,,,"11100000","1~

faulty behaviour
[00:00:07.657,379] <dbg> lte_lc.at_handler: +CEREG notification: +CEREG: 2,"AF9C","00AA6A65",9 [00:00:07.657,592] <inf> cloud: CIOT_NETWORK_CONNECTING [00:00:07.657,592] <wrn> ct: New cell id: 0x00aa6a65 [00:00:07.657,592] <wrn> ct: New tracking area code: 0xaf9c [00:00:07.657,623] <dbg> at_notif.notif_dispatch: Done [00:00:07.657,623] <dbg> at_cmd.socket_thread_fn: Writing any pending command [00:00:07.657,653] <dbg> at_cmd.socket_thread_fn: Listening on socket

This is the point, the modem hangs up. CEREG:5 (for connection, roaming) is not reached.

There are just two ways to solve the problem:

• power cycle
• wait for exactely 30 minutes. Then the modem is apparently restarted (?)

[Didrik Rokhaug]

Hi,

What modem FW version are you using?

If you are using mfw v1.3.0, it sounds like you have triggered the modem's reset loop detection.

If you subscribe to %MDMEV notifications, the modem will report that it has activated the reset loop restriction.

You can find more information in our nRF9160 Modem Reset Loop Restriction whitepaper and the AT command reference.

Best regards,

Didrik

[Paul Kajdewicz]

That has solved the problem. Thanks a lot for the fast answer!

But I have one question regarding the reboot behaviour:
From my understanding a COLD restart should invoke the same behaviour, as a power cycle, right?

It apparently does not behave the same way.

In addition to this, a software restart ends in the following function

void __weak sys_arch_reboot(int type)
{
       ARG_UNUSED(type);

       NVIC_SystemReset();
}

, which omits the WARM/COLD parameter. Is this still to be implemented?

[Didrik Rokhaug]

Hi, and sorry for the late reply.

I believe the only way to reset the nRF9160 from software is via NVIC_SystemReset(), which will do a soft or warm reset.

Best regards,

Didrik