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Modem open after ended transmission

thireo

Dear Devzone

I have an NB-IoT application running on a Thingy:91, that wakes up every two minutes and sends a small package over TCP to a remote server.  
I'm using a Keithley DMM6500 to measure the current consumption, and from that it is clearly visible that the modem doesn't not power down after sending the data. The current consumption is high (~30+mA) for at least 20 seconds after transmission has been completed. This of course ruins the average current consumption.
I have tried using different Power Saving Modes (PSM) with an active time as low as possible (a couple of seconds). The PSM mode is accepted by the network, but does not change the described behaviour. I have also tried different network vendors but without success.

I see similar behaviour when using the Asset Tracker example project.

Is this intended behaviour?

Modem firmware: 1.1.0

Best Regards, Andreas (Thireo)

  • 0 in reply to Håkon Alseth

    Hi Håkon

    I finally got the DMM6500 to do what's supposed to. Please see the attached figure for a complete cycle.

    And yes, I'm still seeing unwanted behaviour.

    Best regards,
    Andreas

  • 0 in reply to thireo

    Hi Andreas,

     

    Thanks for the detailed scope.

    It looks like your current active time is approx. 30 seconds.

    Does this correlate with the return from CEREG?

    I see now that I have flipped the former return values from CEREG.

    +CEREG: 1,"76C1","014A0305",7,,,"00100001","00000110"

    00100001 is the active time, 001 = minute, 1 * 1 minute is your active time from the former scenario.

    00000110 is the TAU (sleep period), 000 = 10 minutes, 10 min * 6 = 1 hour, is the sleep period from the former example.

     

    Kind regards,

    Håkon

  • 0 in reply to Håkon Alseth

    Hi Håkon

    I have just double checked the results from my CEREG requests. It responds with:
    +CEREG: 5,1,"61B4","02781248",9,,,"00000001","00000110"

    Which from my interpretation should equal to 2 seconds active time and 3600 seconds sleep period.

    Enabling LTE control debugging seems to confirm this:
    "[00:04:11.449,127] <dbg> lte_lc.lte_lc_psm_get: TAU: 3600 sec, active time: 2 sec"

    Best regards,
    Andreas

  • 0 in reply to thireo

    Hi Andreas,

     

    Are you enabling the GPS? That will also draw 30 to 40 mA (depending on what the CPU is up to)

    Could you try the same setup with at_client and see if this also behaves similar?

    There are delays in terms of when asset_tracker sends data, especially when GPS is enabled, as the GPS only runs when in PSM or eDRX mode.

     

    Kind regards,

    Håkon

  • 0 in reply to Håkon Alseth

    Hi Håkon

    No GPS is not enabled. At least not that I'm aware of. In prj.conf systemmode is set to "CONFIG_LTE_NETWORK_MODE_NBIOT". 
    The build generated .config file for zephyr seems to confirm my assumption:
    "# CONFIG_LTE_NETWORK_MODE_LTE_M is not set
    # CONFIG_LTE_NETWORK_MODE_LTE_M_GPS is not set
    CONFIG_LTE_NETWORK_MODE_NBIOT=y
    # CONFIG_LTE_NETWORK_MODE_NBIOT_GPS is not set"

    Could you give me some pointers as to how I'm supposed to send data via AT commands. I have yet to find any information regarding this, in the datasheets for NRF9160.

    Best regards,
    Andreas

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