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,
Which SIM card are you using when you try to connect to the NB-IoT network (xsystemmode=0,1,0,0) ?

AT&T and Verizon do not have NB-IoT support according to GSMA, which would explain why you do not get attached to the network.
Please notice the responses from the CEREG, there you can see what the status of the modem is.
e.g. 

<stat>
0 – Not registered. User Equipment (UE) is not currently searching for an operator to register to.
1 – Registered, home network.
2 – Not registered, but UE is currently trying to attach or searching an operator to register to.
3 – Registration denied.
4 – Unknown (e.g. out of E-UTRAN coverage).
5 – Registered, roaming.
8 – Attached for emergency bearer services only.
90 – Not registered due to Universal Integrated Circuit Card (UICC) failure.

[miked531]

I'm using a SIM from Deutche Telekom. It was just an assumption that I could connect to nb-iot. It's actually good that I cannot so I have a reasonable test case for when the device gets sent off to who-knows-where that doesn't support it. Included is the log from my application today, trying to connect to nb-iot.

From what I can tell:

1. from 00:29 to 01:05 it tries to register with a couple different towers and at 01:05 the network tells me essentially to "leave me alone" with the +CGEV: RESTR 2,2
2. an hour later, starting at 01:03:39 we repeat the process (the application tries to connect every 60 minutes)
3. after another hour, at 02:09:55 we repeat. this time, we don't get any RESTR or CEREG stat = 4 responses
4. finally, the last few lines I ran manually hours later. you can see +CFUN is 4 and CEREG status is 2

It is the last two things (no CEREG=4 in the 3rd cycle, and CEREG=2 when CFUN is 4) that I am concerned about.

[00:00:03.294,891] <inf> modem: send: AT%XSYSTEMMODE=0,1,0,0
[00:00:03.296,905] <inf> modem: got: OK
[00:00:03.296,936] <inf> modem: send: AT+CFUN=1
[00:00:03.297,149] <inf> modem: got: OK
[00:00:03.297,149] <inf> modem: send: AT%XSYSTEMMODE?
[00:00:03.327,636] <inf> modem: got: OK
[00:00:03.328,796] <inf> modem: got: %XSYSTEMMODE: 0,1,0,0
[00:00:03.328,857] <inf> modem: got: OK
[00:00:03.328,887] <inf> modem: send: AT+CGMI
[00:00:03.329,223] <inf> modem: got: Nordic Semiconductor ASA
[00:00:03.329,254] <inf> modem: got: OK
[00:00:03.329,254] <inf> modem: send: AT+CGMM
[00:00:03.329,589] <inf> modem: got: nRF9160-SICA
[00:00:03.329,620] <inf> modem: got: OK
[00:00:03.329,650] <inf> modem: send: AT+CGMR
[00:00:03.329,956] <inf> modem: got: mfw_nrf9160_1.1.0
[00:00:03.329,986] <inf> modem: got: OK
[00:00:03.330,017] <inf> modem: send: AT+CGSN
[00:00:03.330,352] <inf> modem: got: 352656100038754
[00:00:03.330,383] <inf> modem: got: OK
[00:00:03.330,383] <inf> modem: send: AT+CIMI
[00:00:03.330,688] <inf> modem: got: ERROR
[00:00:03.330,718] <inf> modem: send: AT+CEREG=2
[00:00:03.330,993] <inf> modem: got: OK
[00:00:03.331,024] <inf> modem: send: AT%CESQ=1
[00:00:03.331,329] <inf> modem: got: OK
[00:00:03.331,359] <inf> modem: send: AT+CGEREP=1
[00:00:03.331,665] <inf> modem: got: OK
[00:00:29.140,502] <inf> lte: got: %CESQ: 67,3,18,2
[00:00:29.140,655] <inf> lte: got: +CEREG: 2,"131B","0112393B",9
[00:00:29.737,548] <inf> lte: got: +CEREG: 4,"131B","0112393B",9
[00:00:29.992,370] <inf> lte: got: %CESQ: 255,0,255,0
[00:00:29.992,553] <inf> lte: got: +CEREG: 4,"FFFE","FFFFFFFF",9
[00:00:39.849,822] <inf> lte: got: %CESQ: 60,3,18,2
[00:00:39.849,975] <inf> lte: got: +CEREG: 2,"6A81","019E9B0A",9
[00:00:40.664,459] <inf> lte: got: %CESQ: 255,0,255,0
[00:00:40.664,642] <inf> lte: got: +CEREG: 2,"FFFE","FFFFFFFF",9
[00:01:05.449,768] <inf> lte: got: %CESQ: 59,2,16,2
[00:01:05.449,829] <inf> lte: got: +CGEV: RESTR 2,2
[00:01:05.449,951] <inf> lte: got: +CEREG: 2,"6D82","01AAD614",9
[00:02:05.610,351] <inf> lte: got: +CEREG: 2,"6A81","019E9B0A",9
[00:02:34.772,460] <inf> lte: got: %CESQ: 59,2,21,3
[00:03:39.850,769] <inf> modem: send: AT+CFUN=4
[00:03:39.881,988] <inf> lte: got: %CESQ: 255,0,255,0
[00:03:39.882,141] <inf> lte: got: +CEREG: 0,"6A81","019E9B0A",9
[00:03:39.929,107] <inf> modem: got: OK
[01:03:39.891,632] <inf> modem: send: AT%XSYSTEMMODE=0,1,0,0
[01:03:39.893,676] <inf> modem: got: OK
[01:03:39.893,707] <inf> modem: send: AT+CFUN=1
[01:03:39.923,645] <inf> modem: got: OK
[01:05:42.274,322] <inf> lte: got: %CESQ: 60,3,17,2
[01:05:42.274,475] <inf> lte: got: +CEREG: 2,"6D82","01AAD614",9
[01:05:43.480,133] <inf> lte: got: %CESQ: 255,0,255,0
[01:05:43.480,316] <inf> lte: got: +CEREG: 2,"FFFE","FFFFFFFF",9
[01:06:24.436,370] <inf> lte: got: %CESQ: 43,2,21,3
[01:06:24.436,492] <inf> lte: got: +CEREG: 2,"EE0B","00C526D3",9
[01:06:25.002,136] <inf> lte: got: %CESQ: 255,0,255,0
[01:06:25.002,319] <inf> lte: got: +CEREG: 2,"FFFE","FFFFFFFF",9
[01:06:26.994,781] <inf> lte: got: %CESQ: 67,3,21,3
[01:06:26.994,934] <inf> lte: got: +CEREG: 4,"131B","0112393B",9
[01:08:03.295,867] <inf> lte: got: %CESQ: 67,3,26,3
[01:08:08.118,988] <inf> lte: got: %CESQ: 62,3,21,3
[01:08:08.119,079] <inf> lte: got: +CGEV: RESTR 2,2
[01:08:08.119,171] <inf> lte: got: +CEREG: 2,"6D82","01AAD614",9
[01:08:11.957,427] <inf> lte: got: +CEREG: 4,"131B","0112393B",9
[01:08:28.896,484] <inf> lte: got: %CESQ: 67,3,21,3
[01:08:34.016,601] <inf> lte: got: %CESQ: 67,3,26,3
[01:09:55.720,245] <inf> lte: got: %CESQ: 61,3,20,2
[01:09:55.720,336] <inf> lte: got: +CGEV: RESTR 2,2
[01:09:55.720,428] <inf> lte: got: +CEREG: 2,"6D82","01AAD614",9
[01:10:21.711,975] <inf> lte: got: %CESQ: 61,3,15,2
[01:10:21.712,158] <inf> lte: got: +CEREG: 2,"6A81","019E9B0A",9
[01:10:21.712,219] <inf> lte: got: +CGEV: RESTR 2,2
[01:10:50.872,955] <inf> lte: got: %CESQ: 61,3,20,2
[01:12:55.727,416] <inf> modem: send: AT+CFUN=4
[01:12:55.746,429] <inf> lte: got: %CESQ: 255,0,255,0
[01:12:56.035,461] <inf> modem: got: OK
[02:09:55.727,539] <inf> modem: send: AT%XSYSTEMMODE=0,1,0,0
[02:09:55.729,583] <inf> modem: got: OK
[02:09:55.729,614] <inf> modem: send: AT+CFUN=1
[02:09:55.759,643] <inf> modem: got: OK
[02:09:55.759,643] <inf> lte: set modem mode OFFLINE -> NORMAL
[02:12:06.933,532] <inf> lte: got: %CESQ: 39,1,21,3
[02:12:06.933,685] <inf> lte: got: +CEREG: 2,"EE0B","00C526D3",9
[02:12:07.499,328] <inf> lte: got: %CESQ: 255,0,255,0
[02:12:07.499,511] <inf> lte: got: +CEREG: 2,"FFFE","FFFFFFFF",9
[02:12:08.683,776] <inf> lte: got: %CESQ: 58,2,16,2
[02:12:08.683,929] <inf> lte: got: +CEREG: 2,"6A81","019E9B0A",9
[02:12:09.498,413] <inf> lte: got: %CESQ: 255,0,255,0
[02:12:09.498,565] <inf> lte: got: +CEREG: 2,"FFFE","FFFFFFFF",9
[02:12:34.283,752] <inf> lte: got: %CESQ: 59,2,17,2
[02:12:34.283,843] <inf> lte: got: +CGEV: RESTR 2,2
[02:12:34.283,935] <inf> lte: got: +CEREG: 2,"6D82","01AAD614",9
[02:12:55.726,928] <inf> modem: send: AT+CFUN=4
[02:12:55.739,990] <inf> lte: got: %CESQ: 255,0,255,0
[02:12:56.028,503] <inf> modem: got: OK

hours later, and manually I get:

AT+CFUN?
+CFUN: 4
OK
AT+CEREG?
+CEREG: 0,2,"6D82","01AAD614",9
OK

[Martin Lesund]

Try to run the AT%XEPCO=0 before turning on the modem when selecting NB-IoT (AT%XSYSTEMMODE).

[miked531]

Tried and got the same results. Also tried AT%XEPCO=1 and no difference

[Martin Lesund]

Awaiting modem trace for further analysis. 

[miked531]

1104.traces.zip

includes logs+traces for successful catm1 connection and failed nbiot connection

[miked531]

Martin Lesund is there any update?

[Martin Lesund]

Using the T-Mobile SIM when you try to connect on the LTE-M network, you are Roaming on the AT&T network.
Using the T-Mobile SIM when you try to connect to the NB-IoT network you are not finding the T-Mobile network.

Please check with T-Mobile if you have NB-IoT coverage in your area.

[miked531]

I am aware that I cannot connect to NB-IoT in my area. I'm OK with that. In fact, I am happy that I am not able to connect as I need to ensure my application functions in all cases. My concern is that things get wonky after the connection fails... AT+CEREG reports that it is still in searching mode (status 2). Additionally, all subsequent LTE-M connections take an inordinate amount of time (~80 seconds), and if I did NOT attempt NB-IoT connection, the LTE-M connection would succeed in <5 seconds.

The current solution in my application is to reset the device after a NB-IoT connection fails. I can deal with that but it's not a good solution.

I appreciate the support you have been providing, but after a month, I don't feel we are any closer to identifying what's happening. I don't know what is going on, but something doesn't seem right. I would appreciate a willingness from Nordic to accept that there something is maybe a little off. I'm even fine with guidance that tells me that I am doing something wrong, or that I should expect the results that I am seeing. Telling me repeatedly that NB-IoT is not connecting is not helping. I know that. Please help me so I can make a solid product.