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前言
要让手机能够控制手表，第一步当然要让手机能够“看见”手表，人类作为上帝视角，我们是能够通过眼睛直接看见手机和手表的，但要让手机“看见”手表，就需要一端把自己的信息通过电磁波的形式发往空中，另一端接收到空中的电磁波信号识别到需要的信息，从而感知到对端并与对端握手和后续的交互。完成上述的过程这里需要引入两个概念广播和连接。本章主要讲解如何让两个设备“见面”。
ble广播类型
| 广播类型 | 意义 |
|---|---|
| 通用广播 | 既可以被主动扫描到，也可以被连接的广播方式，是最常用的广播方式 |
| 定向广播 | 报文里含有广播者地址和发起者地址，发起者设备收到发给自己的定向广播报文后，可以立即发送连接请求给对方 |
| 不可连接广播 | 只能广播数据，不能响应主动扫描或者连接 |
| 可发现广播 | 不能被连接，但可以广播数据或者响应主动扫描 |
这里就我们常用的广播报文–通用广播抓包分析下
广播报文格式
报头格式
广播报文类型
| 广播报文类型 | 含义 |
|---|---|
| ADV_IND | 通用广播指示 |
| ADV_DIRECT_IND | 定向连接指示 |
| ADV_NONCONN_IND | 不可连接指示 |
| ADV_SCAN_IND | 可扫描指示 |
| SCAN_REQ | 主动扫描请求 |
| SCAN_RSP | 主动扫描响应 |
| CONNECT_REQ | 连接请求 |
发送地址类型
长度
对于广播报文，长度域包含6个比特，有效值的范围是6-37个字节。广播报文除了最多31个字节的数据外，还要包含6个字节的广播设备地址，6个字节加31个字节导致报文长度最多为37个字节，因此需要6比特的长度域
数据
广播包中的数据域使用LTV的格式进行定义，即 length + type + value
length表示(type + value)的总长度;
type为1byte数据类型，蓝牙协议规范定义类型如下：
/// The type of advertising data(not adv_type)
typedef enum {ESP_BLE_AD_TYPE_FLAG = 0x01, /* relate to BTM_BLE_AD_TYPE_FLAG in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_16SRV_PART = 0x02, /* relate to BTM_BLE_AD_TYPE_16SRV_PART in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_16SRV_CMPL = 0x03, /* relate to BTM_BLE_AD_TYPE_16SRV_CMPL in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_32SRV_PART = 0x04, /* relate to BTM_BLE_AD_TYPE_32SRV_PART in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_32SRV_CMPL = 0x05, /* relate to BTM_BLE_AD_TYPE_32SRV_CMPL in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_128SRV_PART = 0x06, /* relate to BTM_BLE_AD_TYPE_128SRV_PART in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_128SRV_CMPL = 0x07, /* relate to BTM_BLE_AD_TYPE_128SRV_CMPL in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_NAME_SHORT = 0x08, /* relate to BTM_BLE_AD_TYPE_NAME_SHORT in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_NAME_CMPL = 0x09, /* relate to BTM_BLE_AD_TYPE_NAME_CMPL in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_TX_PWR = 0x0A, /* relate to BTM_BLE_AD_TYPE_TX_PWR in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_DEV_CLASS = 0x0D, /* relate to BTM_BLE_AD_TYPE_DEV_CLASS in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_SM_TK = 0x10, /* relate to BTM_BLE_AD_TYPE_SM_TK in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_SM_OOB_FLAG = 0x11, /* relate to BTM_BLE_AD_TYPE_SM_OOB_FLAG in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_INT_RANGE = 0x12, /* relate to BTM_BLE_AD_TYPE_INT_RANGE in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_SOL_SRV_UUID = 0x14, /* relate to BTM_BLE_AD_TYPE_SOL_SRV_UUID in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_128SOL_SRV_UUID = 0x15, /* relate to BTM_BLE_AD_TYPE_128SOL_SRV_UUID in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_SERVICE_DATA = 0x16, /* relate to BTM_BLE_AD_TYPE_SERVICE_DATA in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_PUBLIC_TARGET = 0x17, /* relate to BTM_BLE_AD_TYPE_PUBLIC_TARGET in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_RANDOM_TARGET = 0x18, /* relate to BTM_BLE_AD_TYPE_RANDOM_TARGET in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_APPEARANCE = 0x19, /* relate to BTM_BLE_AD_TYPE_APPEARANCE in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_ADV_INT = 0x1A, /* relate to BTM_BLE_AD_TYPE_ADV_INT in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_LE_DEV_ADDR = 0x1b, /* relate to BTM_BLE_AD_TYPE_LE_DEV_ADDR in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_LE_ROLE = 0x1c, /* relate to BTM_BLE_AD_TYPE_LE_ROLE in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_SPAIR_C256 = 0x1d, /* relate to BTM_BLE_AD_TYPE_SPAIR_C256 in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_SPAIR_R256 = 0x1e, /* relate to BTM_BLE_AD_TYPE_SPAIR_R256 in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_32SOL_SRV_UUID = 0x1f, /* relate to BTM_BLE_AD_TYPE_32SOL_SRV_UUID in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_32SERVICE_DATA = 0x20, /* relate to BTM_BLE_AD_TYPE_32SERVICE_DATA in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_128SERVICE_DATA = 0x21, /* relate to BTM_BLE_AD_TYPE_128SERVICE_DATA in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_LE_SECURE_CONFIRM = 0x22, /* relate to BTM_BLE_AD_TYPE_LE_SECURE_CONFIRM in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_LE_SECURE_RANDOM = 0x23, /* relate to BTM_BLE_AD_TYPE_LE_SECURE_RANDOM in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_URI = 0x24, /* relate to BTM_BLE_AD_TYPE_URI in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_INDOOR_POSITION = 0x25, /* relate to BTM_BLE_AD_TYPE_INDOOR_POSITION in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_TRANS_DISC_DATA = 0x26, /* relate to BTM_BLE_AD_TYPE_TRANS_DISC_DATA in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_LE_SUPPORT_FEATURE= 0x27, /* relate to BTM_BLE_AD_TYPE_LE_SUPPORT_FEATURE in stack/btm_ble_api.h */ESP_BLE_AD_TYPE_CHAN_MAP_UPDATE = 0x28, /* relate to BTM_BLE_AD_TYPE_CHAN_MAP_UPDATE in stack/btm_ble_api.h */ESP_BLE_AD_MANUFACTURER_SPECIFIC_TYPE = 0xFF, /* relate to BTM_BLE_AD_MANUFACTURER_SPECIFIC_TYPE in stack/btm_ble_api.h */
} esp_ble_adv_data_type;部分常见类型定义解析如下：
抓包分析
结尾
到这里广播篇基本就告一段落了，当然实际中还需要结合具体的场景做分析，主要关注以上几个关键点即可以完成广播相关的操作，下章将介绍如何进行连接，未完待续！