This application is a Zephyr-based Bluetooth LE Audio Broadcast Source application supporting multiple subgroups.

The application is a slightly modified version of the BAP Broadcast Source sample.

If you haven't done it yet, first go to The Zephyr getting started guide and install all dependencies (I'd recommend following the path with the virtual python environment).

For developers of the application, first do a fork of the repo. Then do the following:

Make a local workspace folder (to hold the repo, zephyr and west modules):

mkdir my-workspace
cd my-workspace

Clone the repo:

git clone [email protected]:<your handle>/multisubgroup-source.git

Initialize west and update dependencies:

west init -l multisubgroup-source
west update

This repo contains a stand alone Zephyr application that can be fetched and initialized like this:

west init -m https://github.com/astraeuslabs/multisubgroup-source --mr main my-workspace

Then use west to fetch dependencies:

cd my-workspace
west update

To prepare and add stream files to the project, follow these steps:

1. Prepare the Audio Files: Obtain or create audio files in .wav format (with a sample rate of 16, 24, or 48 kHz, in either Mono or Stereo channels).
2. Encode with LC3: Use the LC3 encoder tool (available at https://github.com/google/liblc3/), to encode the .wav files into LC3 format.
3. Add Encoded Files to the Project: Copy the encoded .lc3 files into the app/src/lc3/ directory of the project.
4. Modify lc3_audio.h: Edit the lc3_audio.h file, to include the names of the stream files and update the streams metadata accordingly. Also, adjust the NUM_STREAM_FILES value, add or remove the stream_data definitions, and update the corresponding array sizes and data in the lc3_audio.h file.

To modify the number of subgroups, streams per subgroup, sample rate, or audio channel mode:

• Adjustments in prj.conf

  • Subgroup and stream configuration

    • Set CONFIG_BT_BAP_BROADCAST_SRC_SUBGROUP_COUNT to the desired number of subgroups.
    • Set CONFIG_BT_BAP_BROADCAST_SRC_STREAM_COUNT to the total number of streams (subgroups × streams per subgroup).

  • ISO channel and buffer configuration (if total streams > 6)

    • Set CONFIG_BT_ISO_MAX_CHAN to at least the total number of streams.
    • Set CONFIG_BT_ISO_TX_BUF_COUNT to at least three times the total number of streams.

  • Audio sample rate (if not using the default 16 kHz)

    • Uncomment CONFIG_BT_BAP_AUDIO_SR_24K=y for a 24 kHz sample rate.
    • Uncomment CONFIG_BT_BAP_AUDIO_SR_48K=y for a 48 kHz sample rate.

  • Audio channel mode (if not using the default Mono)

    • Uncomment CONFIG_BT_BAP_AUDIO_CH_STEREO=y for "Stereo".
    • Uncomment CONFIG_BT_BAP_AUDIO_CH_LCR=y for "LCR" (Left-Center-Right).

    NOTE: For Mono, Stereo, and LCR audio channel modes, the number of streams per subgroup is 1, 2, and 3, respectively.

• Adjustments to controller configuration in overlay-bt_ll_sw_split.conf (if needed)

  • Stream configuration for controller (if total streams > 6)
    • Set CONFIG_BT_CTLR_ADV_ISO_STREAM_MAX to at least the total number of streams.
    • Set CONFIG_BT_CTLR_ISOAL_SOURCES to at least the total number of streams.

Navigate to the repository folder:

cd multisubgroup-source

To build the application for the nRF52840 dongle, run the following command (ensure you are in the virtual environment):

west build -b nrf52840dongle -d build/nrf52840dongle/app app --pristine -- "-DEXTRA_CONF_FILE=overlay-bt_ll_sw_split.conf"

After building, create the firmware package with::

nrfutil pkg generate --hw-version 52 --sd-req=0x00 --application build/nrf52840dongle/app/zephyr/zephyr.hex --application-version 1 build/build_dongle.zip

To flash the created package to the dongle:

• Enter DFU Mode: Press the small side button on the dongle using a nail or similar tool. The dongle's red LED should begin fading in and out, indicating it is in DFU mode.
• Flash the Package: Run the following command, replacing /dev/ttyACMx with the appropriate device (e.g., /dev/ttyACM0, /dev/ttyACM1, etc.):

nrfutil dfu serial -pkg build/build_dongle.zip -p /dev/ttyACMx

NOTE: To identify the correct device, you can list active serial devices before and after connecting the dongle:

ls /dev/ttyACM*

As an alternative to manual configuration, you can use the provided script to automatically generate the configuration, build the firmware, and flash it to the nRF52840 dongle. Run the following commands in sequence: Alternatively, you can use the provided scripts to modify project config, build and flash the nRF52840 dongle. Execute them in the following order:

./config_build_flash.sh -g -sg <number of desired subgroups> -sr <16k/24k/48k> -ch <mono/stereo/lcr>
./config_build_flash.sh -b
./config_build_flash.sh -p
./config_build_flash.sh -f -dd /dev/ttyACMx

• Replace /dev/ttyACMx with the correct device identifier.
• Ensure the dongle is in DFU mode as described above.

NOTE: You can also combine multiple steps into a single command. For full usage instructions, run:

./config_build_flash.sh -h