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蓝牙笔记

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  1. 分类

通常由两种形式

  1. 传统蓝牙BR(Basic Rate),如蓝牙耳机和音响等

  2. 低功耗蓝牙(Bluetooth Low Energy),如蓝牙手环等Iot设备

  3. 数据传输模型

L2CAP Layer Logical Layer Physical Layer L2CAP Channels Logical Links Logical Transports Physical Links Physical Channel

分为三层,数据发送时由高层逐层向下流动,接收时相反

  1. L2CAP

  2. Logical

Logical层主要完成BLE通信过程中的各种逻辑控制,在一次BLE通信过程中,存在master和slave两方,master主动扫描并发起连接,slave则不断广播等待连接,下图为一次通信过程中master和slave的状态,scanner和davertiser分别表示amster和slave的扫描状态和广播状态,建立连接之后,开始调频通信

Stand By Scanner Initiator Master CAN RS ONNECr RE Frequency H Stand By ADV_IND DIRECT IND Advertiser ADV SCAN IND ADV NONCONN IND Slave

  1. Physical

Physical层定义了3个广播信道和37个数据通信信道,在两个蓝牙设备进行连接的过程中,先随机挑选一个广播信道进行广播,待建立连接之后,会在37个通信信道上进行跳频通信

Android BLE接口

在TCP的socket通信中,服务端程序运行于某一IP地址上,并持续监听某个port,客户端程序选择服务端的IP和port发起socket连接,经过三次TCP握手之后完成socket连接的建立并使用该socket进行通信.

蓝牙也是如此,需要先扫描走位蓝牙设备,并选择某个BLE设备,此时需用到以下API

接口名称 所属类 接口描述
startScan bluetoothLeScanner 开始扫描周围BLE设备
stopScan bluetoothLeScanner 结束扫描

扫描并完成选择后就需要与之通信,会用到以下API

接口名称 所属类 接口描述
writeCharacteristic BluetoothGatt 读写指定Characteristic
readCharacteristic BluetoothGatt 读写指定Characteristic

在每一个BLE设备中都会有一个对应的profile用于对这个设备进行描述,一个peofile中包含多个service,为该设备提供各种服务,在一个service中又会有多个characteristic,设备提供的service就是靠这些characteristic来完成

33A83S IN * 13 umOuMu 冖 」 一 一 ㄇ 凵

9:40 Devices BONDED CONNECTED NOT BONDED Generic Access UI-JD: PRIMARY SERVICE Device Name UI-JD: Ox2AOO 4.3K/s.* Z O ADVERTISER CLIENT DISCONNECT 0000 SERVER Properties: READ, WRITE Value: Appearance UI-JD: Ox2A01 Properties: READ [0] Unknown Value: Peripheral Privacy Flag UI-JD: Ox2A02 Properties: READ, WRITE Value: Privacy is disabled in this device Peripheral Preferred Connection Parameters I-JUD: Ox2A04 Properties: READ Value: Connection Interval: 125.00ms - 250.00ms, Slave Latency: 0, Supervision Timeout Multiplier: 2000 Reconnection Address UI-JD: Ox2A03 Properties: READ, WRITE, WRITE NO RESPONSE Value: Generic Attribute UI-JD: PRIMARY SERVICE Service Changed I-JUD: Ox2A05 Properties: INDICATE, READ Descriptors: Client Characteristic Configuration I-JUD: Value: Indications enabled Device Information UI-JD: Ox180A PRIMARY SERVICE Serial Number String I-JUD: Ox2A25 Properties: READ Value: Oc8080b345 Software Revision String UI-JD: Ox2A28 Properties: READ Value: vo.2.2 System ID UI-JD: Ox2A23 Properties: READ (Ox) 88-0F-10-FF-FE-80-B3-45 Value: PnP ID UI-JD: Ox2A50 Properties: READ Value: Bluetooth SIG Company: Anhui Huami Information Technology Co., Ltd. <0x0157> Product Id: 36897 Product Version: 36 Weight Scale UI-JD: Ox181D PRIMARY SERVICE Current Time UI-JD: Ox2A2B Properties: READ, WRITE Value: 1 Jan 2226, 00:10:54, Day of week: Unknown Fractions: 0 / 256 s Weight Scale Feature UI-JD: Ox2A9E Properties: READ Weight Measurement I-JUD: Ox2A9D Properties: INDICATE Value: Weight: 4.300 kg Time: 1 Jan 2226, Descriptors: Client Characteristic Configuration I-JUD: Value: Indications enabled Unknown Characteristic UI-JD: 00002a2f-OOOO-3512-2118-0009af100700 Properties: NOTIFY, WRITE Descriptors: Client Characteristic Configuration UI-JD: Value: Notifications enabled Unknown Service UI-JD: 00001530-0000-3512-2118-0009af100700 PRIMARY SERVICE Unknown Characteristic UI-JD: 00001531-0000-3512-2118-0009af100700 Properties: NOTIFY, WRITE Descriptors: Client Characteristic Configuration UI-JD: Value: Notifications enabled Unknown Characteristic UI-JD: 00001532-0000-3512-2118-0009af100700 Properties: WRITE NO RESPONSE Peripheral Preferred Connection Par... UI-JD: Ox2A04 Properties: NOTIFY, READ, WRITE Descriptors: Client Characteristic Configuration UI-JD: Value: Notifications enabled Unknown Characteristic I-JUD: 00001542-0000-3512-2118-0009af100700 Properties: NOTIFY, WRITE Descriptors: Client Characteristic Configuration I-JUD: Value: Notifications enabled