Bluetooth A2DP Source Example

Overview

This project turns a BK7258 board into a Bluetooth Classic A2DP Source. It reads an MP3 file from an SD card, decodes it to PCM, encodes it as SBC, and sends it to a Bluetooth speaker or headset (A2DP Sink).

The a2dp_player serial CLI supports discovery, connection management, playback control, and AVRCP absolute-volume control.

> This is a Bluetooth Classic (BR/EDR) example, not a BLE example. The board initiates the connection to the speaker/headset.

Features

Discover, connect to, and disconnect from Bluetooth speakers/headsets
Play an MP3 file from an SD card (1:/ FATFS drive)
Playback control: play, pause, resume, stop, previous, and next
AVRCP playback-status reporting and peer absolute-volume control
A2DP performance test command

Hardware and test environment

BK7258 reference board
Bluetooth speaker or headset supporting A2DP Sink; AVRCP is required for remote-control and absolute-volume tests
SD card formatted for FATFS and containing MP3 files
Serial terminal for boot logs and CLI commands

Directory structure

central/
├── ap/
│   ├── ap_main.c                         # AP entry; initializes SDK/media service and registers CLI
│   ├── a2dp_source/
│   │   ├── a2dp_source_demo.c            # A2DP Source connection and MP3 playback logic
│   │   ├── a2dp_source_demo_avrcp.c      # AVRCP control/status reporting
│   │   └── a2dp_source_demo_cli.c        # ``a2dp_player`` CLI
│   ├── storage/                          # Bluetooth storage helpers
│   └── config/bk7258_ap/config           # AP configuration
├── cp/
│   ├── cp_main.c                         # CP entry; starts the AP system
│   └── config/bk7258/config              # CP configuration
└── partitions/bk7258/                    # BK7258 partition and RAM-region definitions

The AP side owns the media and profile demo logic. The CP side starts the AP and provides the Bluetooth controller configuration.

Build and flash

Run the command from the SDK root:

CCACHE_DISABLE=1 make bk7258 PROJECT=bluetooth/central -j$(nproc)

Flash the generated firmware with the normal BK7258 flashing procedure, then insert the SD card.

Quick start

Open a serial terminal after boot.
Discover nearby Bluetooth devices:
```
a2dp_player discover
```
Connect to the speaker/headset found in the log:
```
a2dp_player connect XX:XX:XX:XX:XX:XX
```
Play an MP3 file from the SD card:
```
a2dp_player play 1:/music.mp3
```

Stop playback and disconnect when finished:

a2dp_player stop
a2dp_player disconnect XX:XX:XX:XX:XX:XX

CLI commands

The following are AP CLI commands. When entering them through the default CP serial console, prepend ap_cmd; for example, enter ap_cmd a2dp_player discover. When using an AP CLI directly, enter the commands exactly as listed below. Use a2dp_player -h to print command help.

Command | Description |
— | — |
a2dp_player discover [sec] [count] | Scan for nearby Bluetooth devices; default duration is 10 seconds and count=0 means no report limit. |
a2dp_player discover_cancel | Stop an ongoing discovery. |
a2dp_player connect <MAC> | Connect to an A2DP Sink device. |
a2dp_player disconnect <MAC> | Disconnect a remote device. |
a2dp_player play 1:/music.mp3 | Decode and stream an MP3 file from the SD card. |
a2dp_player pause / resume / stop | Control the current playback. |
a2dp_player prev / next | Request previous/next playback; this demo does not provide a playlist manager. |
a2dp_player abs_vol <0-127> | Set the peer AVRCP absolute volume. |
a2dp_player test_performance [cpu_mhz] [bytes] [loops] [cpu_id] | Run the A2DP Source performance test. |

<MAC> must be written as XX:XX:XX:XX:XX:XX.

Verification

CMDRSP:OK means only that the CLI accepted the command. Confirm successful operation from the Bluetooth profile and media logs:

after connect, A2DP/AVRCP connection events should be reported;
after play, the remote speaker/headset should play audio and MP3 decode/SBC send logs should appear;
after abs_vol, the remote volume should change if it supports AVRCP absolute volume.

Notes

The MP3 path must use the SD-card FATFS drive, for example 1:/music.mp3.
The A2DP Source sources are included whenever CONFIG_BT is enabled. ap_main.c registers a2dp_player; the A2DP Source service is initialized on the first connect command, not at boot. The project Kconfig still labels its menu as “Headset Example Configuration” and contains the unrelated A2DP_SINK_DEMO symbol; that symbol does not start this Source demo.
prev and next exercise playback-control handling only; they do not select files from a playlist.