AIROC™ BTSTACK: Bluetooth® A2DP source for Linux host

The code example demonstrates an A2DP source using AIROC™ Wi-Fi & Bluetooth® combo chip on Linux platform.

The application acts as an audio streaming source device and can be connected to A2DP Sink devices such as headset, earphones, or speaker. When a remote A2DP sink and local A2DP device is set in pairable mode and devices are successfully bonded, the application saves the peer's Bluetooth® device address to its bonded device list. Once the connection is made, the audio stream starts on the A2DP source and the application streams the audio from the local audio file selected for the remote A2DP sink (headset or speaker) that is already connected. The application supports Bluetooth® Standard SBC encoder and sampling frequencies of 44.1 kHz and 48 kHz. The application supports reading and encoding of 44.1 kHz and 48 kHz .wav format files. The CE supports a maximum of 1 paired device.

View this README on GitHub.

Provide feedback on this code example.

Requirements

• Programming language: C
• Embedded Linux platforms (Arm® Cortex®-A Class processors) for host communications. Supported Embedded Linux host platforms:
  1. RPI CM4-lite IFX custom HW board from Infineon
  2. IMX8 nano uCOM board from Embedded Artists
• AIROC™ BTSTACK library and Linux porting layer source code
• AIROC™ Wi-Fi & Bluetooth® combo chip Bluetooth® Firmware file (.hcd).
• Linux Host PC with Ubuntu 20.04

Supported toolchains (make variable 'TOOLCHAIN')

• GNU Arm® GCC AArch64 v9.3.0 (GCC_ARM)

Supported AIROC™ Wi-Fi & Bluetooth® Combo Chip

• AIROC™ CYW5557x Wi-Fi & Bluetooth® Combo Chip

Hardware setup

Set up the hardware according to the following diagram:

Figure 1. Block diagram: Hardware setup

Software setup

Set up a cross compiler according to the target platform along with CMake on the Linux host PC based on Ubuntu 20.04.

1. Open a terminal on the Ubuntu host PC.

2. Use the following command to install the cross compiler, build tools, and dependencies:

   sudo apt-get install git cmake gcc-aarch64-linux-gnu build-essential -y

Using the code example

Do the following on the Host Linux PC to compile the code example:

1. Create a directory under $HOME on the Linux host PC and switch to the created directory. Use the following commands, for example:

   mkdir $HOME/Linux_CE
   cd $HOME/Linux_CE

   Note: Replace Linux_CE with a directory of your choice.

2. Fetch the code example source code using the following command:

   git clone https://github.com/Infineon/linux-example-btstack-a2dp-source

3. Clone or prepare the code example dependencies (BTSTACK library, Linux porting layer, audio profiles source code, and Linux audio library) using the following commands and hints:

   git clone https://github.com/Infineon/btstack --branch release-v3.6.0
   git clone https://github.com/Infineon/bluetooth-linux.git --branch release-v2.0.0
   git clone https://github.com/Infineon/bt-audio-profiles.git --branch release-v1.0.0

   Four different directories are created after cloning the code example and its dependencies; see the following image:

   Figure 2. Code example directory structure

   

4. Clone the Bluetooth® firmware using following command:

   git clone https://github.com/Infineon/combo-bluetooth-firmware.git

   User can choose appropriate Bluetooth® firmware for particular AIROC™ Wi-Fi & Bluetooth® combo chip from cloned "combo-bluetooth-firmware" directory.

5. Create the build folder under the code example source folder and build the code example using the following commands:

   cd $HOME/Linux_CE/linux-example-btstack-a2dp-source
   mkdir build && cd build
   cmake -DCMAKE_C_COMPILER:PATH=<GCC_CROSS_COMPILER> ../ && make

   Where,

   • GCC_CROSS_COMPILER is the target cross compiler for GCC (generally /usr/bin/aarch64-linux-gnu-gcc for ARM64-based targets)

   The code example executable is generated under the build folder with the same name.

   For example, in this project, the "linux-example-btstack-a2dp-source" executable is generated at /home/$USER/Linux_CE/linux-example-btstack-a2dp-source/build.

Features demonstrated

• A2DP connection to sink
• A2DP audio stream configuration
• Start Streaming
• Stop Streaming
• A2DP Disconnection

Operation

The code example acts as an A2DP source. The remote device will be the A2DP sink like Bluetooth® speaker, Bluetooth® headset, and so on.

Devices used

• Device Under Test (DUT): Embedded Linux host platforms with AIROC™ Wi-Fi & Bluetooth® Combo Chip (target platform) that runs the A2DP source code example.

  Role: "A2DP Source"

• Testing device: Bluetooth® speaker or headset

  Role: "A2DP Sink"

1. Copy the code example executable, AIROC™ BTSTACK library, audio profiles source code, Linux audio library, and Bluetooth® Firmware file from the Linux host PC to the target platform using SCP. For example, use the following commands.

   cd $HOME/Linux_CE/linux-example-btstack-a2dp-source/build
   scp linux-example-btstack-a2dp-source <TARGET_USER>@<TARGET_IP>:<TARGET_PATH>/.
   cd $HOME/Linux_CE/btstack/stack/COMPONENT_WICED_DUALMODE/COMPONENT_ARMv8_LINUX/COMPONENT_GCC
   scp libbtstack.so <TARGET_USER>@<TARGET_IP>:<TARGET_PATH>/.
   cd $HOME/Linux_CE/bt-audio-profiles/sbc/COMPONENT_ARMv8_LINUX/COMPONENT_GCC
   scp libsbc.so <TARGET_USER>@<TARGET_IP>:<TARGET_PATH>/.
   cd $HOME/Linux_CE/combo-bluetooth-firmware/<COMBO_CHIP>/<PACKAGE>/.
   scp <FW_FILE.hcd> <TARGET_USER>@<TARGET_IP>:<TARGET_PATH>/.

   Where,

   • TARGET_USER is the user name of the target platform.
   • TARGET_IP is the IP address of the target platform.
   • TARGET_PATH is the path of the target platform.
   • COMBO_CHIP is AIROC™ Wi-Fi & Bluetooth® combo chip name
   • PACKAGE is AIROC™ Wi-Fi & Bluetooth® combo chip package
   • FW_FILE.hcd file is Bluetooth® Firmware file cloned in step-4 of Using the code example section.

2. Copy the required sample audio files that are streamed to the remote sink:

   cd $HOME/Linux_CE/linux-example-btstack-a2dp-source/audio_test_files
   scp 44K.wav <TARGET_USER>@<TARGET_IP>:<TARGET_PATH>/.
   scp 48K.wav <TARGET_USER>@<TARGET_IP>:<TARGET_PATH>/.

   "44K.wav" is for 44.1-kHz sampling frequency and "48K.wav" is for 48-kHz sampling frequency.

3. Take SSH console of target platform.

   ssh <TARGET_DEVICE_USER_NAME>@<TARGET_DEVICE_IP_ADDRESS>

4. Add the udev rule in the target board for HCI UART and GPIO to bypass root access. Use the following steps to create and set up a udev rule.

   Note: If you have root access, the following udev rules are not required; you can execute the code example with sudo permissions or by switching to the root user.

   1. Create a new .rules (for example, combo-chip-uart-port.rules) file under /etc/udev/rules.d/ directory for HCI UART. Use the following commands:

      IMX8Nano:

      echo "KERNEL==\"ttymxc0\"d,SYMLINK+=\"combo_chip_uart\",MODE=\"0666\"" | sudo tee /etc/udev/rules.d/combo-chip-uart-port.rules

      RPICM4:

      echo "KERNEL==\"ttyAMA0\",SYMLINK+=\"combo_chip_uart\",MODE=\"0666\"" | sudo tee /etc/udev/rules.d/combo-chip-uart-port.rules

   2. Create new .rules (for example, combo-chip-gpio-port.rules) for BT_REG_ON GPIO under /etc/udev/rules.d/. Use the following commands:

      IMX8Nano and RPICM4:

      1. Create a rule file using the following command.

         sudo vim /etc/udev/rules.d/combo-chip-gpio-port.rules.rules

      2. Add the following rules in created files:

         SUBSYSTEM=="gpio*", PROGRAM="/bin/sh -c 'chown -R $user:$group /sys/class/gpio/export /sys/class/gpio/unexport;'"
         SUBSYSTEM=="gpio*", PROGRAM="/bin/sh -c 'chown -R $user:$group /sys%p/direction /sys%p/value; chmod 660 /sys%p/direction /sys%p/value;'"

   3. Reboot the target device:

      sudo reboot

      Where,

      • ttymxc0 and ttyAMA0 are HCI UART ports for IMX8Nano and RPICM4 respectively
      • combo_chip_uart is a friendly name for the HCI UART port
      • 0666 is the permission mask to bypass the root access for HCI UART

5. Execute the application with setting the paths of the AIROC™ BTSTACK library using the following command on the target platform:

   cd <TARGET_PATH>
   chmod +x <APP_NAME>
   LD_LIBRARY_PATH=$LD_LIBRARY_PATH:<BTSTACK_LIB_PATH>
   ./<APP_NAME> -c <COM_PORT> -b 3000000 -f 921600 -r <GPIOCHIPx> <REGONPIN> -n -p <FW_FILE_NAME>.hcd -d 112233221137

   Where,

   • APP_NAME is the code example application executable

   • TARGET_PATH is the path of the target platform where the code example application copied to

   • BTSTACK_LIB_PATH is the path of the AIROC™ BTSTACK library. Skip this if the AIROC™ BTSTACK library and code example application executable are in the same folder

   • /dev/ttymxc0 is the COM_PORT for IMX8Nano

   • /dev/ttyAMA0 is the COM_PORT for RPICM4

   • 3000000 is the HCI baud rate

   • 112233221137 is a device BD address

   • -r <GPIOCHIPx> <REGONPIN> -n is setting the GPIO control to enable autobaud for AIROC™ Wi-Fi & Bluetooth® combo chip

     • -r gpiochip5 0 -n For IMX8Nano
     • -r gpiochip0 3 -n For RPICM4

   • 921600 is the firmware download baud rate

   • .hcd is the firmware file to download (make sure to validate this firmware file file path)

     Note-1: Currently, random BD addresses are used for testing.
     Note-2: The CE supports a maximum of one paired device. If the user is connecting to a new device, then the nvramxxx.bin should be deleted on the DUT.

6. The following menu is presented on the console for the user to choose from:

         =================================
               A2DP source menu
         ---------------------------------
            0.  Exit
            1.  Read Local BD address
            2.  Set Pairing Mode
            3.  Inquiry
            4.  Connect A2DP Sink
            5.  Disconnect A2DP Sink
            6.  Stream Configure
            7.  Stream Start
            8.  Stream Stop
         =================================
         Choose option (0-8):

7. Use the following sequence to validate A2DP Source functionality:

   1. Set pairing mode, select option #2 and then #1 to allow pairing.
   2. Discover the Bluetooth® devices that are in the range. Select option #3 and then #1 to start inquiry. Bluetooth® address, Class of Device and RSSI values of remote devices are displayed as a result of inquiry.
   3. Note down Bluetooth® address of A2DP Sink device and cancel the ongoing inquiry. Select Option #3 and then #0.
   4. Connect to A2DP Sink device. Select option #4 and enter Bluetooth® address of A2DP sink device in XX XX XX XX XX XX format.
   5. Configure the stream for required sampling frequency: (1- 48 kHz, 2- 44.1kHz). Select option #6 and then select require sampling frequency using option #1 or #2.
   6. Once configured, the user can start streaming. This option streams to the already connected device. The audio file name for 44.1-kHz frequency is embedded in the code as "44K.wav" and for 48-kHz frequency, it is "48K.wav". Select option #7 to start stream.

8. User can choose to terminate stream and connection. This can be done after using the streaming feature.

   1. Terminate currently streaming A2DP music. Select option #8.
   2. Disconnect the already connected Sink. Select option #5.
   3. Close A2DP source application. select option #0.

   Audio files should be present in the current directory of the application binary. (For reference, check 'audio_test_files' folder in this source directory). Developer can change the files in the source or rename new files to these names in order to test.
   CAUTION: This code example loads the entire file into a buffer; therefore, if developers are using a larger file, it may result in memory faults. They can choose to modify the logic to read partial file contents as required.

Debugging

You can debug the example using a generic Linux debugging mechanism such as the following:

• Debugging by logging: You can add prints in the application and check it during the execution.

• Debugging using GDB: See GDB man page for more details.

Design and implementation

This code example does the following:

1. Parses the command-line arguments

2. Initializes the AIROC™ BTSTACK library for the AIROC™ Wi-Fi & Bluetooth® Combo Chip

3. Registers the A2DP source service with the Stack.

Figure 3. A2DP source process flowchart

4. Waits until there is connection with an A2DP source device.

5. Initializes the Platform audio driver and the SBC decoder.

6. Waits for the audio stream start.

7. On receiving the audio data from source, the application calls the SBC decoder to decode audio packets and streams the PCM data to the audio driver.

8. It continues step 7 until it receives the Pause, Disconnect, or Exit application.

Note: Run the application without any arguments to get details of the command-line arguments.

Source files

Files	Description of files
app/main.c	Implements the main function which takes the user command-line inputs. Calls the a2dp_source.c functions for all the A2DP Source profile functionalities.
app/a2dp_source.c	Implements all functionalities related to A2DP Source.
app_bt_config/wiced_bt_cfg.c	This file is pre-generated using “Bluetooth® configurator” on Windows. This file contains configurations related to BT settings, GAP and A2DP source.
app_bt_utils/app_bt_utils.c	Contains all the utility functions. For example, it contains functions to print error codes, status, etc. in a user-understandable format.
app_bt_utils/app_bt_utils.h	Header file corresponding to app_bt_utils.c
include/a2dp_source.h	Header file corresponding to a2dp_source.c.

Resources and settings

Table 1. Application resources

Resource	Alias/object	Purpose
UART	HCI	UART is used for HCI communication with host system

Related resources

Resources	Links
Device documentation	CYW5557x
AIROC™ BTSTACK library	AIROC™ BTSTACK library
Linux porting layer source code	Linux porting layer source code

Other resources

Infineon provides a wealth of data at www.infineon.com to help you select the right device, and quickly and effectively integrate it into your design.

Document history

Document title: CE236896 – AIROC™ BTSTACK: Bluetooth® A2DP source for Linux host

Version	Description of change
1.0.0	New code example

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