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  • Case ID: 349117
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Modem network notifications delayed

kuchx

Hello,

I am working on nRF9160 custom board. Since I am reprogramming a lot, this issue is kind of getting on my nerves. Here is the issue:

Usually modem takes couple of seconds after initialization to turn on the RRC module and create a connection to network. But sometimes after some failed connections to server or just reset, the modem takes multiple minutes to receive the RRC notification and its getting frustrating. Once it was like 14 minutes, I tried reprogramming FW, downgrading and upgrading modem FW, but nothing really helped. And then after couple of times waiting for the connection to establish, on the next reset it started to work fine again. In past 2 weeks this already happened twice - once it took 4 minutes to connect and since yesterday it takes 12 minutes to receive the RRC notification and establish connection with network. I have not changed my location so the Cell is the same every time. The Cell ID notification is received within seconds since startup but the RRC for some reason takes super long time. 

I tried searching through already existing tickets but I can't really relate to those issues, some of them mention operator change or cell change, but that for me is stationary. So for obvious reasons I think the modem for some reason went rogue and I still haven't found a way to properly recover it. Since our FW currently waits around 30 seconds to get network connection, means that when modem in this state will never connect to network and device is pretty much useless. 30 seconds because its a battery powered device and usually that is enough for the modem to connect to network.

So my questions are:

1) Is this something you are aware of?

2) Why the modem re-flashing does not help?

3) Since re-flashing does not work, is it because the modem HW is somehow damaged but then again why does it bounce back to normal operation?

4) How I can properly recover modem in this situation?

5) Is the same issue observed on nRF9151 SiP?

I am currently using 1.3.7 modem version and if it makes any difference working on 2.6.0 SDK. Operating in LTE-M

Regards,

Andris

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  • 0 in reply to Benjamin

    Hi Benjamin,

    While I was trying to add the modem trace to our current code and testing it on device the modem started to function normally again. Here is a trace but I believe you won't see anything out of the ordinary in it! 


    Can we leave this ticket open and I will get back to you with a trace when the modem delay appears again? Since now I have a already working code for tracing I believe next time it happens I will be able to record it.

    Also I'll be on a vacation next two weeks, so I'll get back to developing device code in 18.08 in case you start to wonder where I disappeared.

    Regards,

    Andris

  • 0 in reply to kuchx

    No problem at all, just come back when you're ready. Enjoy your vacation!

  • 0 in reply to Benjamin

    Hello Benjamin,

    The issue reappeared and I managed to get a modem trace. It took about 24 minutes before MCU received the RRC connected notification from modem, but as before it took a couple of seconds since startup to receive Cell ID notification. 

    Regards,

    Andris

  • +1 in reply to kuchx

    Hi Andris,
    The issue is caused by the reset loop restriction, which can occur if the device is flashed frequently.

    To prevent this, put the modem into offline mode before flashing or powering off the device. You can also reset the reset loop counter using the AT%XFACTORYRESET command.

    Best regards,
    Benjamin

  • 0 in reply to Benjamin

    Hi Benjamin,

    I was aware of this reset loop protection but I am not really convinced that this is actually the case. If it actually would be reset loop protection, then I would expect that after successfully creating connection in the given trace, at the next reset device would immediately attach to network for the next at least 6 reset times, since the timer was expired. But that was not the case.

    I noticed this also before when the RRC connected notification took about 7 minutes to be received - I waited for the attach, device worked for a while, restarted it and again I would have to wait the same timeout. 

    Another question - if I remove power from the device, the reset loop counter froze's (at least that's what I expect)? In some cases the issue appeared at the end of the work day and I shut it down, came back the next morning and issues still persisted.

    Anyhow I still don't believe that the issue here is reset loop counter regarding the very first paragraph of this answer. Hope this gives you some more insights about the issue. Or maybe I don't fully understand the working concept of the reset loop counter? Let me know what are your thoughts on this

    Best regards,

    Andris

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