Bluetooth

The MB-E30P development board integrates the RTL8723DU wireless communication module. This module not only provides WIFI functionality but also integrates Bluetooth functionality. The Bluetooth module supports both Classic Bluetooth and Bluetooth Low Energy (BLE) protocols, providing the development board with rich short-range wireless communication capabilities.

1 Bluetooth Module Overview

1.1 RTL8723DU Bluetooth Specifications

ParameterSpecification
Chip ModelRealtek RTL8723DU
Bluetooth VersionBluetooth 4.2
Protocol SupportClassic Bluetooth + BLE (Bluetooth Low Energy)
Operating Frequency Band2.4GHz ISM band (2.402~2.480GHz)
ModulationFHSS (Frequency Hopping Spread Spectrum)
Transmit PowerClass 2 (maximum 4dBm)
Receive Sensitivity-90dBm @ 0.1% BER
Transmission Range10 meters (Class 2)
Data RateMaximum 3Mbps (EDR)

1.2 Driver and Software Support

Linux Bluetooth Protocol Stack

  • BlueZ: Standard Linux Bluetooth protocol stack
  • Kernel Support: Native kernel driver support
  • Userspace Tools: bluetoothctl, hciconfig, hcitool, etc.
  • D-Bus Interface: Standard D-Bus API interface

Supported Application Scenarios

  • Audio Devices: Bluetooth headsets, speaker connections
  • Input Devices: Bluetooth keyboard, mouse
  • File Transfer: File exchange with phones, computers
  • Serial Communication: Bluetooth serial data transmission
  • IoT Applications: BLE sensor data collection

2 Bluetooth Connection Configuration

The development board has adapted the RTL8723DU module; the Bluetooth driver and protocol stack have been configured.

2.1 Connection Test

The test requires a smartphone (an Android phone was used for this section's testing). Turn on the phone's Bluetooth function, and also turn on the development board's Bluetooth function, then connect, as shown in the figure below:

BT

Development board side:

BT_3

Phone side:

BT_4

2.2 Data Send/Receive Test

First, create a new bluetooth_test.txt file in the home/linaro folder, with the content: bluetooth_test.

BT_2

1) File Sending

The development board sends bluetooth_test.txt to the phone via Bluetooth, and the phone receives it.

Development board side:

BT_5

Phone side:

BT_6

Check whether the file contents are consistent:

BT_7

2) File Receiving

The phone sends bluetooth_test.txt to the development board via Bluetooth, and the development board receives it.

Phone side:

BT_8
BT_9

Development board side:

BT_10
BT_11

2.3 Command-Line Bluetooth Configuration

hciconfig and hcitool

# 查看蓝牙适配器信息
hciconfig -a

# 启用蓝牙适配器
sudo hciconfig hci0 up

# 设置可发现模式
sudo hciconfig hci0 piscan

# 扫描附近设备
hcitool scan

# 查看设备信息
hcitool info XX:XX:XX:XX:XX:XX

# 检查连接状态
hcitool con

Pairing and Authentication

# 使用 simple-agent 配对
sudo simple-agent hci0 XX:XX:XX:XX:XX:XX

# 或使用 bluez-simple-agent
bluez-simple-agent hci0 XX:XX:XX:XX:XX:XX

3 Bluetooth Audio Applications

3.1 Connecting Bluetooth Audio Devices

Installing Audio Support Packages

# 安装 PulseAudio 蓝牙模块
sudo apt-get install pulseaudio-module-bluetooth

# 重启 PulseAudio
pulseaudio -k
pulseaudio --start

Configuring Audio Devices

# 查看音频设备
pactl list short sinks

# 设置默认音频输出
pactl set-default-sink bluez_sink.XX_XX_XX_XX_XX_XX.a2dp_sink

# 播放测试音频
speaker-test -t wav -c 2

# 使用 aplay 播放音频文件
aplay /usr/share/sounds/alsa/Front_Left.wav

3.2 A2DP Audio Streaming

# 连接 A2DP 设备后，检查音频配置
bluetoothctl
[bluetooth]# info XX:XX:XX:XX:XX:XX

# 在 PulseAudio 中查看蓝牙音频设备
pactl list sinks | grep -A 10 bluez

# 播放音频到蓝牙设备
mpg123 -a bluez_sink.XX_XX_XX_XX_XX_XX.a2dp_sink music.mp3

4 BLE (Bluetooth Low Energy) Applications

BLE Device Scanning and Connection

Using gatttool

# 扫描 BLE 设备
sudo hcitool lescan

# 连接 BLE 设备
gatttool -b XX:XX:XX:XX:XX:XX -I

# 在 gatttool 交互模式中：
[XX:XX:XX:XX:XX:XX][LE]> connect
[XX:XX:XX:XX:XX:XX][LE]> primary        # 列出主要服务
[XX:XX:XX:XX:XX:XX][LE]> characteristics # 列出特征值
[XX:XX:XX:XX:XX:XX][LE]> char-read-hnd 0x0010  # 读取特征值
[XX:XX:XX:XX:XX:XX][LE]> char-write-req 0x0010 0100  # 写入特征值

Using bluetoothctl for BLE Operations

bluetoothctl
[bluetooth]# scan on
[bluetooth]# connect XX:XX:XX:XX:XX:XX
[bluetooth]# gatt list-attributes
[bluetooth]# gatt select-attribute /org/bluez/hci0/dev_XX_XX_XX_XX_XX_XX/service0010/char0011
[bluetooth]# gatt read
[bluetooth]# gatt write "0x01 0x02"

5 Troubleshooting

5.1 Bluetooth Module Cannot Be Recognized

Inspection Steps:

# 检查 USB 设备
lsusb | grep Realtek

# 检查蓝牙适配器
hciconfig -a

# 检查内核模块
lsmod | grep bluetooth

# 手动加载蓝牙模块
sudo modprobe bluetooth
sudo modprobe btusb

# 检查蓝牙服务状态
sudo systemctl status bluetooth

5.2 Device Pairing Failure

Possible Causes and Solutions:

# 重置蓝牙适配器
sudo hciconfig hci0 reset

# 清除配对缓存
sudo rm -rf /var/lib/bluetooth/*/cache

# 重启蓝牙服务
sudo systemctl restart bluetooth

# 检查认证代理
ps aux | grep agent

5.3 Audio Connection Issues

Resolution Steps:

# 检查 PulseAudio 模块
pactl list modules | grep bluetooth

# 重新加载蓝牙模块
pactl unload-module module-bluetooth-discover
pactl load-module module-bluetooth-discover

# 检查音频配置文件
bluetoothctl
[bluetooth]# info XX:XX:XX:XX:XX:XX

5.4 Unstable Connection

Optimization Suggestions:

# 检查信号强度
hcitool rssi XX:XX:XX:XX:XX:XX

# 调整功率管理
echo 'SUBSYSTEM=="usb", ATTRS{idVendor}=="0bda", ATTRS{idProduct}=="d723", ATTR{power/autosuspend}="-1"' | sudo tee /etc/udev/rules.d/50-usb-bluetooth.rules

# 重启 udev 服务
sudo udevadm control --reload-rules

5.5 File Transfer Failure

Inspection and Repair:

# 检查 OBEX 服务
sudo systemctl status obex

# 安装 OBEX 工具
sudo apt-get install obexftp obex-data-server

# 启动 OBEX 服务
obex-data-server --auto-accept