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  • Case ID: 306549
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The AT+CFUN=0 take long time sometimes

Tim Chao

Hi,

I am developing a low-power device to periodically publish data.

I need to turn off the modem after the publishing task is completed.

And I found that sometimes the AT+CFUN=0 takes a long time to get response.

Below is the code piece for turn-off the modem.

And here are some logs I got.


You can see that sometimes it takes more than 30 seconds to finish.

Is this normal behavior?

PS. I am using NCS 2.3.0 with Modem FW 1.3.3

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  • 0

    Hi,

    Are you using LTE-M or NB-IoT, and how are the signal conditions?

    Detaching from the network involves some communication with the network, so it could be that there are some problems communicating with the network.

    Also, how often do you attach and detach to the network? Most network don't like devices doing that too often, so it could be that the frequency of the tests themselves are causing a problem.

    But, as  said, a modem trace would be very helpful in finding the cause of the delay.

    Best regards,

    Didrik

  • 0 in reply to Didrik Rokhaug

    Hi Didrik,

    Modem trace attached.

    Tested with NRF9160DK with modem_shell, the latest modem power off take >32s.

    trace-2023-04-26T02-13-34.608Z.bin

  • 0 in reply to Tim Chao

    Thanks.

    In the case where the detach takes a long time, it seems like the modem is using that time to search for a cell. However, I don't know why it does that, so I've asked the modem team to have a look at it.

    I'll let you know when they have reached a conclusion.

  • +1 in reply to Didrik Rokhaug

    According to the modem team, "SI reception from first found cell fails and due to that cell selection takes time."

    Before the modem can turn off, it has to send a detach message to the network. In NB-IoT, this process has a max timeout of 85 seconds (i.e. the modem will at most stay active for 85 seconds).

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  • +1 in reply to Didrik Rokhaug

    According to the modem team, "SI reception from first found cell fails and due to that cell selection takes time."

    Before the modem can turn off, it has to send a detach message to the network. In NB-IoT, this process has a max timeout of 85 seconds (i.e. the modem will at most stay active for 85 seconds).

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