蓝牙小记

蓝牙小记，Web Bluetooth Test。

GATT

The Generic Attributes (GATT) define a hierarchical data structure that is exposed to connected Bluetooth Low Energy (LE) devices.

GATT profiles enable extensive innovation while still maintaining full interoperability with other Bluetooth® devices. The profile describes a use case, roles and general behaviors based on the GATT functionality. Services are collections of characteristics and relationships to other services that encapsulate the behavior of part of a device. This also includes hierarchy of services, characteristics and attributes used in the attribute server.

GATT is built on top of the Attribute Protocol (ATT) (see Bluetooth Core System Architecture for block diagram and explanations), which uses GATT data to define the way that two Bluetooth Low Energy devices send and receive standard messages. Note that GATT is not used in Bluetooth BR/EDR implementations, which use only adopted profiles. ¹

GATT 定义了一个由 BLE (Bluetooth Low Energy) 提供的分层数据结构。

GATT 协议使得设备有更好扩展的同时，也能维护一整套和其他蓝牙设备的交互。

分层图大致如下：

gatt profile hierarchy

从图中也能看出，读取蓝牙设备信息的大致步骤

连接蓝牙，也就是连接 GATT Server
获取对应 service，一个蓝牙设备可能有多个 service，比如：电量，血压、心跳频率等等
获取 service 下的 characterristic，比如：电量水平，血压单位（毫米汞柱，千帕），血压数值等
读取数据，解析即可

Demo

jun-30-2018 18-46-19

请使用最新的 Chrome 打开此页面。

Demo Code

      navigator.bluetooth.requestDevice({
        acceptAllDevices: true,
        optionalServices: [
          0x180F, // battery_service https://www.bluetooth.com/specifications/gatt/services
        ]
      }).then(device => {
        // 连接蓝牙
        return device.gatt.connect();
      }).then(server => {
        // battery_service https://www.bluetooth.com/specifications/gatt/services
        // 获取蓝牙指定服务
        return server.getPrimaryService(0x180F);
      }).then(service => {
        // battery_level https://www.bluetooth.com/specifications/gatt/characteristics
        // 获取服务指定 characteristic
        return service.getCharacteristic(0x2A19);
      }).then(characteristic => {
        // 读取数值
        return characteristic.readValue();
      }).then(dataView => {
        console.log(dataView.getInt8(0));
      }).catch(err => {
        console.log(err);
      });

iPhone 蓝牙服务简析

0000180a-0000-1000-8000-00805f9b34fb 0x180A Device Information
- 00002a24-0000-1000-8000-00805f9b34fb 0x2A24 model number: iPhone9,2
- 00002a29-0000-1000-8000-00805f9b34fb 0x2A29 manufacturer name string: Apple Inc.
00001805-0000-1000-8000-00805f9b34fb 0x1815 Automation IO
- 00002a0f-0000-1000-8000-00805f9b34fb Local Time Information: 0x2000
  
  根据官网描述，前8bit 为 TimeZone，并以 15 分钟为单位
  
  0x20 * 15 / 60 = 8, 也就是东 8 区，正确
- 00002a2b-0000-1000-8000-00805f9b34fb Current Time: 0xe207061e151e1006ef02
  
  0xe207：这个值不确定了，2018的16 进制为 0x07e2，不知道是不是前后8位要互调一下
  
  0x06：6月
  
  0x1e：30号
  
  0x15：9点
  
  0x1e：30分
0000180f-0000-1000-8000-00805f9b34fb 0x180F Battery Service
- 00002a19-0000-1000-8000-00805f9b34fb Battery Level: 52
9fa480e0-4967-4542-9390-d343dc5d04ae custom service
- af0badb1-5b99-43cd-917a-a77bc549e3cc
d0611e78-bbb4-4591-a5f8-487910ae4366 custom service
- 8667556c-9a37-4c91-84ed-54ee27d90049

调试小技巧

Chrome 打开 chrome://bluetooth-internals

要是一直连不上，说明之前的连接被刷新了，但在后台还连着，重启 chrome 即可