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Interact with nRF9151 using external third party MCU

bojan

Hello, guys Wave

We want to evaluate nRF9151 SiP the following way:

  • To set it to operate in serial mode in which it is ready to receive AT commands (it comes pre-flashed in that mode on nRF9151-DK, to the best of my understanding)
  • To send AT commands and other necessary GPIO control using some external MCU (not nRF5340 MCU which is populated on nRF9151-DK board but some third party, external MCU)

Few questions related to our goal:

  1. Is it possible to achieve what we want?
  2. Which UART interface should we use for sending AT commands - UART1 or UART2?
  3. In addition to UART Rx/Tx, do we need some other GPIO to control the modem (e.g. Reset, some other GPIO that plays a role in modem control...)?
  4. We would like to test NB-IoT modem by default and switch to LTE-M if needed. How to achieve this, is there any special AT command for switching between available modes (NB-IoT/LTE-M)?

Thanks in advance for your time and efforts. Looking forward to hearing from you.

Sincerely,
Bojan.

  • 0 in reply to Michal

    ... and if we don't want CMUX and PPP features to be implemented in SLM but to have SLM sample behaving as a simple modem that expects AT commands over UART, we would need to re-compile the SLM sample and exclude overlay-cmux.conf and overlay-ppp.conf files from compilation.

    Correct?

  • 0 in reply to bojan

    Those files have to be manually chosen to be used, so you shouldn't need to exclude them specifically.

  • 0 in reply to Michal

    I see the overlay-ppp-without-mux.conf/overlay files in SLM sample app, and I'm wondering what's the difference between PPP with and without CMUX. 

    Anyway, I was able to connect my external third party MCU to the customized SLM sample app and make it communicate with test-endpoint.com server. What I notice is that it's kind of a difficult/impossible for my external MCU to wake up the nRF9151 SiP running SLM app. That's why I used

    CONFIG_SLM_START_SLEEP=n

    flag to have the modem awake on start-up. What is actually needed on CONFIG_SLM_POWER_PIN in order to properly wake up the SLM modem? Toggling, pulse, something more...How do we need to configure the MCU's GPIO that will be used for waking up the SLM?

  • 0 in reply to bojan

     , I found what's wrong with the GPIO of my external MCU that's connected to CONFIG_SLM_POWER_PIN. After fixing it, I was able to detect a proper 100ms wake up pulse on that GPIO. 

    Now, when I flash the version of SLM app with 

    CONFIG_SLM_START_SLEEP=y

    (modem sleeping on start up), cellular_modem sample running on my external MCU can't properly sync-up with SLM app. As you can see from below debug traces, here is what happens in infinite loop:

    1. Wake-up pulse is applied
    2. cellular_modem sample sends AT command
    3. SLM responds with `Ready`. cellular_modem sample treat this as unknown command
    4. cellular_modem goes to step 1 and sends Wake-up pulse again:

    Any help here?

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