NRF52832学习笔记（16）——GAP主机端扫描

一、背景

1.1 蓝牙协议栈

**链路层（LL）**控制设备的射频状态，有五个设备状态：待机、广播、扫描、初始化和连接。

广播 为广播数据包，而 扫描 则是监听广播。

GAP通信中角色，中心设备（Central - 主机） 用来扫描和连接 外围设备（Peripheral - 从机）。

大部分情况下外围设备通过广播自己来让中心设备发现自己，并建立 GATT 连接，从而进行更多的数据交换。

也有些情况是不需要连接的，只要外设广播自己的数据即可，用这种方式主要目的是让外围设备，把自己的信息发送给多个中心设备。

1.2 扫描概念

扫描是一个在一定范围内用来寻址其他低功耗蓝牙设备广播的过程。扫描者设备在扫描过程中会使用广播信道。与广播过程不同的是，扫描过程没有严格的时间定义和信道规则。扫描过程应该按照由 Host 层所设定扫描定时参数还运行。

1.2.1 被动扫描

被动扫描：在被动扫描中，扫描设备应该仅仅去监听广播包，而不向广播设备发送任何数据。

一旦扫描参数设置完成，主机就可以在协议栈中发送命令启动扫描。扫描过程中，如果控制器接收到符合过滤策略或其他规则的广播数据包，则发送一个广播报告事件给主机。报告事件除了有广播者的设备地址外，还包括广播数据包中的数据，以及接收广播数据包时的信号接收强度。我们可以利用该信号强度以及位于广播包中的发射功率，共同确定信号的路径损失，从而给出大致的范围，这个应用就是防丢器和蓝牙定位。

1.2.2 主动扫描

主动扫描：不仅可以捕获到从端设备的广播数据包，还可以捕获扫描响应包，并区分它们。

控制器收到扫描数据后将向主机发送一个广播报告事件（adv_report），该事件包括了链路层数据包的广播类型。因此，主机能够判断从端设备是否可以连接或扫描，并且区分出广播数据包和扫描响应包。

二、配置扫描参数

2.1 扫描参数变量

在 main.c 中

static ble_gap_scan_params_t m_scan_param =											/**< Scan parameters requested for scanning and connection. */
{
    .active        = 0x01,															// 主动扫描
    .interval      = NRF_BLE_SCAN_SCAN_INTERVAL,									// 扫描间隔
    .window        = NRF_BLE_SCAN_SCAN_WINDOW,										// 扫描窗口
    .filter_policy = BLE_GAP_SCAN_FP_ACCEPT_ALL,
    .timeout       = NRF_BLE_SCAN_SCAN_DURATION,									// 扫描超时
    .scan_phys     = BLE_GAP_PHY_1MBPS,
    .extended      = true,
};

• active：是否主动扫描，配置为1则是主动扫描，0则是被动扫描
• interval：扫描间隔，控制器间隔多长时间扫描一次，也就是两个连续的扫描窗口开始时间的时间间隔。在 NRF 上设置为 0x0004 and 0x4000 in 0.625ms units（2.5ms 到 10.24s）
• window：扫描窗口，每次扫描所持续的时间，在持续时间内，扫描设备一直在广播信道上运行。在 NRF 上设置为 0x0004 and 0x4000 in 0.625ms units（2.5ms 到 10.24s）
• filter_policy：扫描筛选策略，也就死说接受任何广播数据或者仅仅接受白名单设备的广播数据包。实际上就死决定是否使用白名单过滤广播数据包。这里注意一点，如果定向广播数据包中的目的地址并非是自己的，那么该数据必须抛弃，即使广播数据包的发送者在自己的白名单中。
• timeout：扫描超时，超过指定的时间后，没有扫描到设备将停止扫描。在 NRF 上设置为 0x0001 and 0xFFFF in seconds，设置为 0 则认为没有 timeout
• scan_phys：扫描的物理层速度

**注意：扫描窗口和扫描间隔两个参数非常重要。扫描窗口的设置要小于或等于扫描间隔，并且都要是 0.625ms 的整倍数。这两个参数决定了主机控制器的扫描占空比。**比如，如果设置扫描间隔为 100 ms，扫描窗口为 10ms ，那么主机控制器的扫描占空比就死 10%。特别注意可以捕获的定向数据包的最低占空比为 0.4%，即每一秒中扫描时间为 3.75ms，这些时间设置在任何蓝牙 4.x 处理器中都是一致的，不仅仅限于 NRF 处理器。

如果把时间间隔设置为相同的大小，那么控制器会进行连续扫描，每个间隔会改变扫描频率，也就死切换扫描信道。

2.2 扫描过滤相关宏

/**@defgroup BLE_GAP_SCAN_FILTER_POLICIES GAP Scanner filter policies
 * @{ */
#define BLE_GAP_SCAN_FP_ACCEPT_ALL                      0x00  /**< Accept all advertising packets except directed advertising packets
                                                                   not addressed to this device. */
#define BLE_GAP_SCAN_FP_WHITELIST                       0x01  /**< Accept advertising packets from devices in the whitelist except directed
                                                                   packets not addressed to this device. */
#define BLE_GAP_SCAN_FP_ALL_NOT_RESOLVED_DIRECTED       0x02  /**< Accept all advertising packets specified in @ref BLE_GAP_SCAN_FP_ACCEPT_ALL.
                                                                   In addition, accept directed advertising packets, where the advertiser's
                                                                   address is a resolvable private address that cannot be resolved. */
#define BLE_GAP_SCAN_FP_WHITELIST_NOT_RESOLVED_DIRECTED 0x03  /**< Accept all advertising packets specified in @ref BLE_GAP_SCAN_FP_WHITELIST.
                                                                   In addition, accept directed advertising packets, where the advertiser's
                                                                   address is a resolvable private address that cannot be resolved. */
/**@} */

• BLE_GAP_SCAN_FP_ACCEPT_ALL：接收所有的广播包，除去广播地址不是指向该设备的定向广播。
• BLE_GAP_SCAN_FP_WHITELIST：接收在白名单里所有的广播，除去广播地址不是指向该设备的定向广播。
• BLE_GAP_SCAN_FP_ALL_NOT_RESOLVED_DIRECTED：接收所有的广播包，包含定向广播包。这里如果广播MAC地址是私密地址，这里是无法被解析的。
• BLE_GAP_SCAN_FP_WHITELIST_NOT_RESOLVED_DIRECTED：接收白名单里所有的广播包，包含定向广播包。这里如果广播MAC地址是私密地址，这里是无法被解析的。

2.3 定义扫描模块

NRF_BLE_SCAN_DEF(m_scan);                                           				/**< Scanning module instance. */

2.4 初始化扫描参数

/**@brief Function for initialization the scanning and setting the filters.
 */
static void scan_init(void)
{
    ret_code_t          err_code;
    nrf_ble_scan_init_t init_scan;

    memset(&init_scan, 0, sizeof(init_scan));

    init_scan.p_scan_param = &m_scan_param;

    err_code = nrf_ble_scan_init(&m_scan, &init_scan, scan_evt_handler);
    APP_ERROR_CHECK(err_code);

    if(strlen(m_target_periph_name) != 0)
    {
        err_code = nrf_ble_scan_filter_set(&m_scan, 
                                           SCAN_NAME_FILTER, 
                                           m_target_periph_name);
        APP_ERROR_CHECK(err_code);
    }

    err_code = nrf_ble_scan_filter_set(&m_scan, 
                                       SCAN_UUID_FILTER, 
                                       &m_adv_uuids[HART_RATE_SERVICE_UUID_IDX]);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_ble_scan_filter_set(&m_scan, 
                                       SCAN_UUID_FILTER, 
                                       &m_adv_uuids[RSCS_SERVICE_UUID_IDX]);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_ble_scan_filters_enable(&m_scan, 
                                           NRF_BLE_SCAN_ALL_FILTER, 
                                           false);
    APP_ERROR_CHECK(err_code);
}

在 main 函数中，执行 scan_init() 进行初始化扫描参数

/**@brief Function for initializing the application main entry.
 */
int main(void)
{
    bool erase_bonds;

	/*-------------------------- 外设驱初始化 ---------------------------*/
    // Initialize.
    log_init();									// 日志驱动初始化

	/*-------------------------- 蓝牙协议栈初始化 ---------------------------*/
    power_management_init();					// 能量初始化
    ble_stack_init();							// 协议栈初始化
	scan_init();								// 扫描初始化
    gap_params_init();
    gatt_init();
	conn_params_init();							// 连接参数初始化
    db_discovery_init();
    peer_manager_init();
	services_init();							// 服务初始化
	advertising_init();							// 广播初始化
	
	/*-------------------------- 开启应用 ---------------------------*/
    // Start execution.
    NRF_LOG_INFO("Relay example started.");

    if(erase_bonds == true)
    {
		NRF_LOG_INFO("delete_bonds");
        // Scanning and advertising is done upon PM_EVT_PEERS_DELETE_SUCCEEDED event.
        delete_bonds();
    }
    else
    {
		NRF_LOG_INFO("adv_scan_start");	
        adv_scan_start();
    }

    // Enter main loop.
    for(;;)
    {
        idle_state_handle();
    }
}

三、开启扫描

包含头文件

#include "nrf_ble_scan.h"

开启扫描函数

/**@brief Function for initializing the scanning.
 */
void scan_start(void)
{
    ret_code_t err_code;

    err_code = nrf_ble_scan_start(&m_scan);
    APP_ERROR_CHECK(err_code);
}

四、关闭扫描

包含头文件

#include "nrf_ble_scan.h"

关闭扫描函数

nrf_ble_scan_stop();

五、广播报告

控制器收到广播数据包后向主机发送一个广播报告事件。

5.1 扫描事件处理

在 main.c 中

/**@brief   Function for handling BLE events from the central application.
 *
 * @details This function parses scanning reports and initiates a connection to peripherals when a
 *          target UUID is found. It updates the status of LEDs used to report the central application
 *          activity.
 *
 * @param[in]   p_ble_evt   Bluetooth stack event.
 */
static void on_ble_central_evt(ble_evt_t const *p_ble_evt)
{
    ret_code_t           err_code;
    ble_gap_evt_t const *p_gap_evt = &p_ble_evt->evt.gap_evt;

    switch(p_ble_evt->header.evt_id)
    {
        ···
        case BLE_GAP_EVT_ADV_REPORT:
            GetAdvReport(p_gap_evt->params.adv_report);
            break;
        ···

5.2 获取广播报告

/**
 @brief 获取广播数据
 @param advReport - 广播报告结构体
 @return 无
*/
void GetAdvReport(ble_gap_evt_adv_report_t advReport)
{
    // 在这里加入对广播报告的处理	
}

5.2.1 ble_gap_evt_adv_report_t

/**@brief Event structure for @ref BLE_GAP_EVT_ADV_REPORT.
 *
 * @note If @ref ble_gap_adv_report_type_t::status is set to @ref BLE_GAP_ADV_DATA_STATUS_INCOMPLETE_MORE_DATA,
 *       not all fields in the advertising report may be available.
 *
 * @note When ble_gap_adv_report_type_t::status is not set to @ref BLE_GAP_ADV_DATA_STATUS_INCOMPLETE_MORE_DATA,
 *       scanning will be paused. To continue scanning, call @ref sd_ble_gap_scan_start.
 */
typedef struct
{
  ble_gap_adv_report_type_t type;                  /**< Advertising report type. See @ref ble_gap_adv_report_type_t. */
  ble_gap_addr_t            peer_addr;             /**< Bluetooth address of the peer device. If the peer_addr is resolved:
                                                        @ref ble_gap_addr_t::addr_id_peer is set to 1 and the address is the
                                                        peer's identity address. */
  ble_gap_addr_t            direct_addr;           /**< Contains the target address of the advertising event if
                                                        @ref ble_gap_adv_report_type_t::directed is set to 1. If the
                                                        SoftDevice was able to resolve the address,
                                                        @ref ble_gap_addr_t::addr_id_peer is set to 1 and the direct_addr
                                                        contains the local identity address. If the target address of the
                                                        advertising event is @ref BLE_GAP_ADDR_TYPE_RANDOM_PRIVATE_RESOLVABLE,
                                                        and the SoftDevice was unable to resolve it, the application may try
                                                        to resolve this address to find out if the advertising event was
                                                        directed to us. */
  uint8_t                   primary_phy;           /**< Indicates the PHY on which the primary advertising packet was received.
                                                        See @ref BLE_GAP_PHYS. */
  uint8_t                   secondary_phy;         /**< Indicates the PHY on which the secondary advertising packet was received.
                                                        See @ref BLE_GAP_PHYS. This field is set to @ref BLE_GAP_PHY_NOT_SET if no packets
                                                        were received on a secondary advertising channel. */
  int8_t                    tx_power;              /**< TX Power reported by the advertiser in the last packet header received.
                                                        This field is set to @ref BLE_GAP_POWER_LEVEL_INVALID if the
                                                        last received packet did not contain the Tx Power field.
                                                        @note TX Power is only included in extended advertising packets. */
  int8_t                    rssi;                  /**< Received Signal Strength Indication in dBm of the last packet received. */
  uint8_t                   ch_index;              /**< Channel Index on which the last advertising packet is received (0-39). */
  uint8_t                   set_id;                /**< Set ID of the received advertising data. Set ID is not present
                                                        if set to @ref BLE_GAP_ADV_REPORT_SET_ID_NOT_AVAILABLE. */
  uint16_t                  data_id:12;            /**< The advertising data ID of the received advertising data. Data ID
                                                        is not present if @ref ble_gap_evt_adv_report_t::set_id is set to
                                                        @ref BLE_GAP_ADV_REPORT_SET_ID_NOT_AVAILABLE. */
  ble_data_t                data;                  /**< Received advertising or scan response data. If
                                                        @ref ble_gap_adv_report_type_t::status is not set to
                                                        @ref BLE_GAP_ADV_DATA_STATUS_INCOMPLETE_MORE_DATA, the data buffer provided
                                                        in @ref sd_ble_gap_scan_start is now released. */
  ble_gap_aux_pointer_t     aux_pointer;           /**< The offset and PHY of the next advertising packet in this extended advertising
                                                        event. @note This field is only set if @ref ble_gap_adv_report_type_t::status
                                                        is set to @ref BLE_GAP_ADV_DATA_STATUS_INCOMPLETE_MORE_DATA. */
} ble_gap_evt_adv_report_t;

• type：广播报告类型
• peer_addr：扫描设备的MAC地址。如果peer_addr被解析，那么参数ble_gap_addr_t::addr_id_peer被设置为1，同时该地址是对等方的身份地址
• direct_addr：扫描定向广播的MAC地址。当参数ble_gap_adv_report_type_t::directed被设置为1，包含目的地址的广播事件。如果协议栈能够解析地址，参数ble_gap_addr_t::addr_id_peer被设置为1，direct_addr包含本地的认证地址。如果广播事件的目的地址是BLE_GAP_ADDR_TYPE_RANDOM_PRIVATE_RESOLVABLE类型，协议栈是服务解析的，应用程序可以尝试解析这个地址，以查明广播是否指向我们
• primary_phy：主广播包的物理层速度
• secondry_phy：第二扩展广播包的物理层速度。看参数BLE_GAP_PHYS。如果在二级广播频道上没有收到信息包，则此字段为0
• tx_power：TX功率报告由广播客户端在最后收到的包头。如果最后收到的数据包不包含TX字段，则这个字段被设置为BLE_GAP_POWER_LEVEL_INVALID
• rssi：接收的信号强度
• ch_index：接收到最后一个广播包的频道（0-39）
• set_id：设置接收广播数据的ID
• data_id：接收的广播数据的广播数据ID
• data：接收的广播数据包或者扫描响应包。如果参数ble_gap_adv_report_type_t::status没有被设置为参数BLE_GAP_ADV_DATA_STATUS_INCOMPLETE_MORE_DATA，参数sd_ble_gap_scan_start中提供的数据缓存立即释放
• aux_pointer：在此扩展广播事件中，下一个广播包的偏移量。注意：只有当ble_gap_adv_report_type_t::status被设置为BLE_GAP_ADV_DATA_STATUS_INCOMPLETE_MORE_DATA时，该字段才会被设置

5.2.2 ble_gap_adv_report_type_t

/**@brief Advertising report type. */
typedef struct
{
  uint16_t connectable   : 1; /**< Connectable advertising event type. */
  uint16_t scannable     : 1; /**< Scannable advertising event type. */
  uint16_t directed      : 1; /**< Directed advertising event type. */
  uint16_t scan_response : 1; /**< Received a scan response. */
  uint16_t extended_pdu  : 1; /**< Received an extended advertising set. */
  uint16_t status        : 2; /**< Data status. See @ref BLE_GAP_ADV_DATA_STATUS. */
  uint16_t reserved      : 9; /**< Reserved for future use. */
} ble_gap_adv_report_type_t;

• connectable：可连接广播事件类型
• scannable：可扫描广播事件类型
• directed：定向广播事件类型
• scan_response：收到扫描响应
• extended_pdu：收到加长广播
• status：数据状态，参考参数BLE_GAP_ADV_DATA_STATUS

/**@defgroup BLE_GAP_ADV_DATA_STATUS GAP Advertising data status
 * @{ */
// 广播包的所有数据已收到
#define BLE_GAP_ADV_DATA_STATUS_COMPLETE             0x00 /**< All data in the advertising event have been received. */
// 需要接收更多的数据
#define BLE_GAP_ADV_DATA_STATUS_INCOMPLETE_MORE_DATA 0x01 /**< More data to be received.
                                                               @note This value will only be used if
                                                               @ref ble_gap_scan_params_t::report_incomplete_evts and
                                                               @ref ble_gap_adv_report_type_t::extended_pdu are set to true. */
// 不完整的数据，缓冲区大小不足以接收更多
#define BLE_GAP_ADV_DATA_STATUS_INCOMPLETE_TRUNCATED 0x02 /**< Incomplete data. Buffer size insufficient to receive more.
                                                               @note This value will only be used if
                                                               @ref ble_gap_adv_report_type_t::extended_pdu is set to true. */
// 未能接收剩余的数据
#define BLE_GAP_ADV_DATA_STATUS_INCOMPLETE_MISSED    0x03 /**< Failed to receive the remaining data.
                                                               @note This value will only be used if
                                                               @ref ble_gap_adv_report_type_t::extended_pdu is set to true. */
/**@} */

• reserved：保留部分

5.2.3 ble_data_t

/**@brief Data structure. */
typedef struct
{
  uint8_t     *p_data;  /**< Pointer to the data buffer provided to/from the application. */
  uint16_t     len;     /**< Length of the data buffer, in bytes. */
} ble_data_t;

• p_data：广播或扫描响应的数据
• len：广播或扫描响应的数据长度

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• 由 Leung 写于 2020 年 3 月 14 日

• 参考：青风电子社区