nRF9160 modem stuck in searching

[miked531]

The modem on the nrf9160DK (modem fw v1.1.0) appears to get stuck in searching mode. It doesn't happen all the time, and I was able to create it with the following AT commands:

(I want to see registration status changes)
AT+CEREG=2
AT%XSYSTEMMODE=0,1,0,0
AT+CFUN=1
(after some time (minutes?) reports AT+CEREG: 2, ...)
(then I see no more +CEREG status reports and give up)
AT+CFUN=4
(wait a few seconds)
AT+CFUN? reports +CFUN: 4, so it seems to have taken the command
AT+CEREG? reports +CEREG: 0,2,"XXXX","XXXXXXXX",9

This all works just fine with %XSYSTEMMODE=1,0,0,0. After the AT+CFUN=4 completes it will report +CEREG: 0,0,...

I kind of expect the connect to work with either mode, as I have good reception from both AT&T and Verizon, but I'm more concerned that the modem appears to get in an *almost* unrecoverable state. Changing systemmode to 1,0,0,0 followed by AT+CFUN=1 returns to normal behavior.

If it helps in troubleshooting, the AT+CFUN=4 takes ~3 seconds in mode 1,0,0,0 and less than 1 sec in mode 0,1,0,0

This link describes a similar issue: https://devzone.nordicsemi.com/f/nordic-q-a/55154/lte-network-detected-but-never-connected

[Martin Lesund]

Hi Mike,
I think I've figured out why it took so long in your cases.

The modem is missing the historical network data in it's flash for some of your use cases, and therefore it will use more time to search and connect.

So what you need to do is to save this data to the modem by issuing the command AT+CFUN=0.

You issue this command after a successful connection, then the next time you try that network in that area it should get a much quicker connection.

[miked531]

Can you please expand on your response.

* The modem quickly connects with lte-m, then is not able to quickly reconnect. If it can do it quickly once, it would seem that the modem flash already has the network data stored. Does it get replaced? Is there a limited number of networks remembered? Also note that after a power reset, the modem returns to the quick connect.

* I thought AT+CFUN=0 turns the modem off after updating it's flash. I played with this some time ago (pre-mfw 1.0) and don't recall any command that could turn it back on. How do I turn it back on?