Nrf9160 reboots with weak signal and then failed connection forever

[feng niao]

Hi, 

I have a nrf9160 device up running for a month and everything looked good. But suddenly it started rebooting periodically, until there is no connection completely. There is watchdog and other scheduled timer to reboot the device in case it gets stuck somewhere or the link is lost.

The RSRP is between 25 and 29 in the area when such reboot happens.

when it reboots, it is able to connect to the nework, send udp packet and receive ack back. However, after sending 5 packets, it reboots again. This scenario repeats 17 times and then there is no reboot and no connection afterwards forever.  And even reboot the device manually, it won´t get connected to the network.

And it can not connect to the network even after taking the device to area with good signal quality around 80 rsrp.

I have following questions

1. After a connection is established and the signal is really weak, when sending the udp packet during PSM mode, if there is issue to connect to the basestation after waking up during RRC setup, will modem reboots by itself? If not, will it asserts and halt the cpu?
2. Do you know what kind of failure can prevent the modem from connecting to the basestation forever? When it fails to connect, I did notice the current went up high just for one second, back to no constant current and then repeat this pattern every 30 seconds. Usually the current changes quite frequently if tries to connect to the network.

NCS 1.2.0 and modem 1.2 is used. Seems there is issue to debug with Ozone, and I can not see how the code is executed with elf file.(Opened the other ticket about debugging issue)

Thanks for reading the bug report and looking forward to your reply. 

[feng niao]

seems it is up running fine again after switching to a new SIM card. Maybe the previous one is broken. 

Can you still give some input on the first question? Thanks.

[Heidi]

Hi!

I'm glad you got the device running fine. 

Yes, I will look into what the modem does when there is a connection issue after waking up during RRC setup. I'll let you know when I find something. 

Best regards,

Heidi

[Heidi]

Hi, I got an answer to your first question.

No, the modem will not reboot by itself if it has trouble establishing an RRC connection due to a weak signal. It shouldn't assert or halt the CPU either. Something else has caused this behavior.

Was the new SIM card from a different operator? If it was, stronger signal could explain why it works as it may connect to a different network. But this leaves the question of why it stopped working with the first SIM card.

If the card was from the same operator as the first SIM card, then I suspect there was something wrong with the first card. A prepaid card that needs more money? If there is a problem with the SIM card, the modem should report some reject cause received from the network. AT+CNEC=24 can be used for getting the error codes. If modem reports error codes they can tell a lot.

If there is no clear reason (no error codes, no need to reload a prepaid card, etc.) and the issue can be reproduced, we could take a modem trace to confirm the behavior.

Best regards,

Heidi

[feng niao]

Hi

Thanks for the information. 

The SIM card is from the same operator. and it is not a prepaid card. 

When I tried to establish the NBIOT link, it replied "CREG: 90", stands for "Non Registered due to UICC Failure". With "AT+CNEC=24", I didn´t get any notification.

Do you know how to initialize the UICC from AT command, so that it can be fixed? I didn´t find any command that I can use. 

[Heidi]

Hi, UICC failure could be due to multiple causes but initializing the UICC won't help. 

Can you provide any information on where you are testing? Any specific network/country? What do you get If you run at_client and AT+CFUN=41? And what does AT%XSIM return?

In this DevZone case for instance, the SIM they were using did not support the correct voltage class.