.. _faq_bp_clock_frequency:

How to set BP Clock Frequency
#############################

The default backplane clock frequency is 16 MHz for ATM33xx and 32 MHz for ATM34xx. Look for the definition of 'system-clock' dts entry in ``openair/dts/arm/atmosic/{ATM33.dtsi, ATM34.dtsi}`` files.

An application may choose to configure different clock frequency overriding the default values by passing build time flags as follows:

.. code-block:: bash

   -DDTS_EXTRA_CPPFLAGS="-DINIT_BP_FREQ=<FREQ>"

For example, to build an application with modified BP clock frequency of 48 MHz, use this command below, with extra arguments:

.. code-block:: bash

   west build -p always -b <BOARD> openair/samples/bluetooth/beacon --sysbuild -T samples.bluetooth.beacon.atm -- -DDTS_EXTRA_CPPFLAGS="-DINIT_BP_FREQ=48000000"

Alternately, application's sysbuild sample.yaml may be modified as follows:

.. code-block:: diff

   git diff sample.yaml
   diff --git a/samples/bluetooth/beacon/sample.yaml b/samples/bluetooth/beacon/sample.yaml
   index be401c45..902c12e2 100644
   --- a/samples/bluetooth/beacon/sample.yaml
   +++ b/samples/bluetooth/beacon/sample.yaml
   @@ -8,6 +8,10 @@ tests:
      samples.bluetooth.beacon.atm:
        sysbuild: true
        harness: console
   +    extra_args:
   +      - SB_ATM_DTS_EXTRA_CPPFLAGS="-DINIT_BP_FREQ=48000000"
        harness_config:
          type: one_line
          regex:

Valid values are 32 MHz, 48 MHz and 64 MHz.