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[docs][bluetooth] Add BlueZ D-Bus architecture documentation
Co-authored-by: supperthomas <[email protected]>
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‎documentation/bluetooth/README.md‎

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# RT-Thread Bluetooth Documentation / RT-Thread 蓝牙文档
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This directory contains documentation about Bluetooth implementation in RT-Thread and comparisons with other Bluetooth stacks.
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本目录包含 RT-Thread 蓝牙实现的相关文档以及与其他蓝牙协议栈的对比。
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## Documents / 文档
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### English
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- [BlueZ vs RT-Thread Bluetooth Implementation](bluez_vs_rtthread_en.md) - Explains the differences between Linux BlueZ (using D-Bus) and RT-Thread's direct Bluetooth implementation
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### 中文
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- [BlueZ 与 RT-Thread 蓝牙实现对比](bluez_vs_rtthread_zh.md) - 解释 Linux BlueZ（使用 D-Bus）与 RT-Thread 直接蓝牙实现的区别
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## Quick Answer / 快速答案
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**Q: What bus does BlueZ use in Linux?**
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**A: BlueZ uses D-Bus (Desktop Bus) as its inter-process communication (IPC) mechanism.**
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**问：Linux 中 BlueZ 使用什么总线？**
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**答：BlueZ 使用 D-Bus（桌面总线）作为其进程间通信（IPC）机制。**
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## Key Takeaways / 要点
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- **Linux BlueZ**: Uses D-Bus for IPC, suitable for desktop/server environments with multiple processes
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- **RT-Thread**: Uses direct function calls, optimized for embedded real-time systems with limited resources
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- **Linux BlueZ**：使用 D-Bus 进行 IPC，适用于具有多个进程的桌面/服务器环境
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- **RT-Thread**：使用直接函数调用，针对资源有限的嵌入式实时系统进行了优化

‎documentation/bluetooth/bluez_vs_rtthread_en.md‎

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# BlueZ Architecture vs RT-Thread Bluetooth Implementation
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## What Bus Does BlueZ Use in Linux?
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### D-Bus Communication Mechanism
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In Linux systems, **BlueZ uses D-Bus (Desktop Bus) as its Inter-Process Communication (IPC) bus**.
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D-Bus is a message bus system that provides a simple way for applications to communicate with each other. BlueZ exposes its API through D-Bus, allowing applications to interact with the Bluetooth daemon (bluetoothd).
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### BlueZ D-Bus Architecture
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```
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┌─────────────────┐
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│ User Applications│
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│ (bluetoothctl, │
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│ apps, etc.) │
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└────────┬────────┘
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│
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│ D-Bus API Calls
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↓
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┌────────────────────┐
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│ D-Bus System Bus │
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│ (Message Broker) │
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└────────┬───────────┘
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│
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│ D-Bus Interface
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↓
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┌────────────────────┐
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│ bluetoothd │
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│ (BlueZ Daemon) │
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└────────┬───────────┘
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│
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│ HCI Protocol
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↓
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┌────────────────────┐
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│ Linux Kernel │
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│ (HCI Driver Layer)│
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└────────┬───────────┘
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│
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↓
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┌────────────────────┐
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│ Bluetooth Hardware │
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│ Controller │
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└────────────────────┘
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```
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### BlueZ D-Bus Interface Examples
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BlueZ provides the following main interfaces on D-Bus:
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1. **org.bluez.Adapter1** - Bluetooth adapter management
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2. **org.bluez.Device1** - Bluetooth device management
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3. **org.bluez.AgentManager1** - Pairing agent management
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4. **org.bluez.ProfileManager1** - Bluetooth profile management
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5. **org.bluez.GattManager1** - GATT service management
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### D-Bus Usage Examples
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```bash
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# Using dbus-send to interact with BlueZ
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dbus-send --system --print-reply \
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--dest=org.bluez \
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/org/bluez/hci0 \
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org.bluez.Adapter1.StartDiscovery
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# Using gdbus to get adapter information
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gdbus call --system \
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--dest org.bluez \
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--object-path /org/bluez/hci0 \
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--method org.freedesktop.DBus.Properties.GetAll \
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org.bluez.Adapter1
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```
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## RT-Thread Bluetooth Architecture
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RT-Thread, as an embedded real-time operating system, adopts a completely different architecture:
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### RT-Thread Bluetooth Communication Architecture
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```
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┌─────────────────┐
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│ RT-Thread Apps │
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│ (Direct API) │
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└────────┬────────┘
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│
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│ Function Calls
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↓
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┌────────────────────┐
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│ RT-Thread Driver │
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│ (drv_bluetooth.c) │
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└────────┬───────────┘
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│
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│ HCI Protocol
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↓
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┌────────────────────┐
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│ UART/USB Interface│
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└────────┬───────────┘
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│
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↓
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┌────────────────────┐
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│ Bluetooth Hardware │
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│ Module │
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└────────────────────┘
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```
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### Key Differences
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| Feature | Linux BlueZ | RT-Thread |
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|---------|-------------|-----------|
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| **IPC Mechanism** | D-Bus | No IPC needed, direct function calls |
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| **Architecture** | User-space daemon + kernel driver | Single address space, integrated driver |
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| **Resource Usage** | Higher (requires D-Bus daemon) | Lower (no additional process overhead) |
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| **Real-time Performance** | Moderate | Excellent (RTOS characteristics) |
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| **API Calls** | Asynchronous D-Bus messages | Synchronous/asynchronous function calls |
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| **Use Cases** | Desktop, server systems | Embedded, IoT devices |
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### RT-Thread Bluetooth API Example
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Bluetooth communication in RT-Thread is implemented through direct function calls:
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```c
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// RT-Thread Bluetooth initialization example
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int rt_hw_bluetooth_init(void)
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{
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bt_uart_protocol_init();
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// Direct function calls, no D-Bus needed
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if (bt_reset() == RT_EOK) {
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rt_kprintf("bluetooth reset ok!\n");
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}
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if (bt_loadfirmware() == RT_EOK) {
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rt_kprintf("loadfirmware ok!\n");
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}
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return RT_EOK;
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}
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```
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## Why Doesn't RT-Thread Use D-Bus?
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1. **Resource Constraints**: Embedded systems have limited memory and processing power; D-Bus overhead is significant
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2. **Real-time Requirements**: RTOS requires deterministic response times; D-Bus message passing adds latency
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3. **Simplified Design**: Direct function calls in a single address space are more efficient
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4. **No Process Isolation Needed**: Embedded systems typically don't require complex inter-process isolation
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## Summary
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- **Linux BlueZ**: Uses D-Bus as an IPC mechanism, suitable for multi-process, multi-user desktop/server environments
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- **RT-Thread**: Uses direct function call approach, suitable for resource-constrained embedded real-time systems
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## References
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- [BlueZ Official Documentation](http://www.bluez.org/)
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- [D-Bus Specification](https://dbus.freedesktop.org/doc/dbus-specification.html)
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- [RT-Thread Programming Guide](https://www.rt-thread.org/document/site/)
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- BlueZ D-Bus API: `/usr/share/doc/bluez/api/` (on Linux systems)

‎documentation/bluetooth/bluez_vs_rtthread_zh.md‎

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# BlueZ 架构与 RT-Thread 蓝牙实现对比
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## Linux 中 BlueZ 使用的总线
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### D-Bus 通信机制
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在 Linux 系统中，**BlueZ 使用 D-Bus（Desktop Bus）作为进程间通信（IPC）总线**。
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D-Bus 是一个消息总线系统，它提供了一种简单的方式让应用程序之间相互通信。BlueZ 通过 D-Bus 暴露其 API，允许应用程序与蓝牙守护进程（bluetoothd）进行交互。
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### BlueZ 的 D-Bus 架构
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```
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┌─────────────────┐
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│ 用户应用程序 │
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│ (bluetoothctl, │
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│ 应用程序等) │
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└────────┬────────┘
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│
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│ D-Bus API 调用
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↓
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┌────────────────────┐
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│ D-Bus 系统总线 │
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│ (消息代理) │
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└────────┬───────────┘
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│
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│ D-Bus 接口
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↓
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┌────────────────────┐
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│ bluetoothd │
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│ (BlueZ 守护进程) │
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└────────┬───────────┘
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│
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│ HCI 协议
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↓
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┌────────────────────┐
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│ Linux 内核 │
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│ (HCI 驱动层) │
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└────────┬───────────┘
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│
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↓
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┌────────────────────┐
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│ 蓝牙硬件控制器 │
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└────────────────────┘
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```
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### BlueZ D-Bus 接口示例
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BlueZ 在 D-Bus 上提供以下主要接口：
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1. **org.bluez.Adapter1** - 蓝牙适配器管理
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2. **org.bluez.Device1** - 蓝牙设备管理
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3. **org.bluez.AgentManager1** - 配对代理管理
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4. **org.bluez.ProfileManager1** - 蓝牙配置文件管理
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5. **org.bluez.GattManager1** - GATT 服务管理
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### D-Bus 使用示例
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```bash
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# 使用 dbus-send 与 BlueZ 交互
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dbus-send --system --print-reply \
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--dest=org.bluez \
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/org/bluez/hci0 \
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org.bluez.Adapter1.StartDiscovery
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# 使用 gdbus 获取适配器信息
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gdbus call --system \
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--dest org.bluez \
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--object-path /org/bluez/hci0 \
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--method org.freedesktop.DBus.Properties.GetAll \
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org.bluez.Adapter1
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```
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## RT-Thread 蓝牙架构
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RT-Thread 作为嵌入式实时操作系统，采用完全不同的架构：
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### RT-Thread 蓝牙通信架构
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```
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┌─────────────────┐
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│ RT-Thread 应用 │
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│ (直接 API) │
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└────────┬────────┘
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│
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│ 函数调用
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↓
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┌────────────────────┐
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│ RT-Thread 驱动 │
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│ (drv_bluetooth.c) │
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└────────┬───────────┘
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│
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│ HCI 协议
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↓
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┌────────────────────┐
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│ UART/USB 接口 │
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└────────┬───────────┘
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│
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↓
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┌────────────────────┐
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│ 蓝牙硬件模块 │
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└────────────────────┘
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```
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### 主要区别
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| 特性 | Linux BlueZ | RT-Thread |
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|------|-------------|-----------|
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| **IPC 机制** | D-Bus | 无需 IPC，直接函数调用 |
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| **架构** | 用户空间守护进程 + 内核驱动 | 单一地址空间，驱动直接集成 |
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| **资源占用** | 较大（需要 D-Bus 守护进程） | 较小（无额外进程开销） |
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| **实时性** | 一般 | 优秀（RTOS 特性） |
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| **API 调用** | 异步 D-Bus 消息 | 同步/异步函数调用 |
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| **适用场景** | 桌面、服务器系统 | 嵌入式、IoT 设备 |
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### RT-Thread 蓝牙 API 示例
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RT-Thread 中的蓝牙通信直接通过函数调用实现：
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```c
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// RT-Thread 蓝牙初始化示例
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int rt_hw_bluetooth_init(void)
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{
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bt_uart_protocol_init();
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// 直接函数调用，无需 D-Bus
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if (bt_reset() == RT_EOK) {
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rt_kprintf("bluetooth reset ok!\n");
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}
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if (bt_loadfirmware() == RT_EOK) {
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rt_kprintf("loadfirmware ok!\n");
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}
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return RT_EOK;
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}
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```
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## 为什么 RT-Thread 不使用 D-Bus？
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1. **资源限制**：嵌入式系统内存和处理能力有限，D-Bus 开销较大
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2. **实时性要求**：RTOS 需要确定性的响应时间，D-Bus 消息传递增加延迟
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3. **简化设计**：单一地址空间下直接函数调用更高效
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4. **无进程隔离需求**：嵌入式系统通常无需复杂的进程间隔离
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## 总结
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- **Linux BlueZ**：使用 D-Bus 作为 IPC 机制，适用于多进程、多用户的桌面/服务器环境
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- **RT-Thread**：采用直接函数调用方式，适用于资源受限的嵌入式实时系统
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## 参考资料
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- [BlueZ 官方文档](http://www.bluez.org/)
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- [D-Bus 规范](https://dbus.freedesktop.org/doc/dbus-specification.html)
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- [RT-Thread 编程指南](https://www.rt-thread.org/document/site/)
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- BlueZ D-Bus API: `/usr/share/doc/bluez/api/`（Linux 系统上）

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