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nRF9160 LFCK setup needed to be done by the app or handled inside bsd-lib?

lobaro-theo

Hello,

the nRF9160 product specification 1.0 states in 5.1.4.2:

"Note: The LTE modem requires using LFXO as the LFCLK source."

I checked the clock register and noticed that bsd lib seems not configure it on init. But the LTE-modem and bsd lib seems to work fine even without setting up the LFXO as the source. So my question:

Is it in the responsibility of the application to setup the LFCLK clock accordingly or does the BSD lib do it internally if needed?
For what tasks the bsd lib and / or LTE modem does use the LFCLK? 

Iam using the bsd lib in our own enviroment (freeRTOS based) without zypher.

Thanks in advance for an explanation what the bsd lib does internally regarding LFCLK configuation.

Greetings
Theo

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  • +1

    Hi Theo,

     

    Is it in the responsibility of the application to setup the LFCLK clock accordingly or does the BSD lib do it internally if needed?
    For what tasks the bsd lib and / or LTE modem does use the LFCLK? 

     There is a lot of timing related operations in the M1 and NB1 protocol, and since they might also be scheduled ahead of time, let's say that you wake up every 120 seconds on eDRX, its crucial to use the LFXO (+/- 20 ppm tolerance) to obtain both low power and best tolerance timing. This is not obtainable if you are using a clock source that has a tolerance in the percent area.

     

    If you are using the modem, you should set LFXO as your 32k clock source.

     

    Kind regards,

    Håko

Reply
  • +1

    Hi Theo,

     

    Is it in the responsibility of the application to setup the LFCLK clock accordingly or does the BSD lib do it internally if needed?
    For what tasks the bsd lib and / or LTE modem does use the LFCLK? 

     There is a lot of timing related operations in the M1 and NB1 protocol, and since they might also be scheduled ahead of time, let's say that you wake up every 120 seconds on eDRX, its crucial to use the LFXO (+/- 20 ppm tolerance) to obtain both low power and best tolerance timing. This is not obtainable if you are using a clock source that has a tolerance in the percent area.

     

    If you are using the modem, you should set LFXO as your 32k clock source.

     

    Kind regards,

    Håko

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