nrf51822---主从通信（1）
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1.目的
学习nrf51822主机和从机通信
2.分析
2个设备，一个做主机一个做从机，相互通信
3.平台：
协议栈版本：SDK10.0.0
编译软件：keil 5.12
硬件平台：nrf51822最小系统
例子：SDK 10.0.0\examples\ble_peripheral\ble_app_uart\pca10028\s110\arm4 从机例子
SDK10.0\examples\ble_central_and_peripheral\experimental\ble_app_hrs_rscs_relay\pca10028\s130\arm4 做主机
4.步骤
1.先把从机的程序下载到一个板子里面
注意:a.32.769khz晶体的选型。b.SDK 以及softwaredevice的版本号
2.来分析下主机的程序
协议栈初始化,串口服务初始化，开始扫描参数初始化以及开始扫描
int main(void){ uint32_t err_code; APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_OP_QUEUE_SIZE, NULL); uart_init(); buttons_leds_init(); ble_stack_init(); err_code = ble_db_discovery_init(); APP_ERROR_CHECK(err_code); nus_c_init(); // Start scanning for peripherals and initiate connection // with devices that advertise NUS UUID. scan_start(); APPL_LOG("Scan started\r\n"); for (;;) { power_manage(); }}这里初始化回调函数，一个串口服务初始化
/**@brief Function for initializing the NUS Client. */static void nus_c_init(void){ uint32_t err_code; ble_nus_c_init_t nus_c_init_t; nus_c_init_t.evt_handler = ble_nus_c_evt_handler; err_code = ble_nus_c_init(&m_ble_nus_c, &nus_c_init_t); APP_ERROR_CHECK(err_code);}这里是最终注册函数，看如下函数
sd_ble_uuid_vs_add(&nus_base_uuid, &p_ble_nus_c->uuid_type); 获得uuid的类型
uuid的类型有
/** @defgroup BLE_UUID_TYPES Types of UUID * @{ */#define BLE_UUID_TYPE_UNKNOWN 0x00 /**< Invalid UUID type. */#define BLE_UUID_TYPE_BLE 0x01 /**< Bluetooth SIG UUID (16-bit). */#define BLE_UUID_TYPE_VENDOR_BEGIN 0x02 /**< Vendor UUID types start at this index (128-bit). *//** @} */uart_uuid.type = p_ble_nus_c->uuid_type; //串口服务的类型
uart_uuid.uuid = BLE_UUID_NUS_SERVICE; //串口主服务的UUID
uint32_t ble_nus_c_init(ble_nus_c_t * p_ble_nus_c, ble_nus_c_init_t * p_ble_nus_c_init){ uint32_t err_code; ble_uuid_t uart_uuid; ble_uuid128_t nus_base_uuid = NUS_BASE_UUID; if ((p_ble_nus_c == NULL) || (p_ble_nus_c_init == NULL)) { return NRF_ERROR_NULL; } err_code = sd_ble_uuid_vs_add(&nus_base_uuid, &p_ble_nus_c->uuid_type); if (err_code != NRF_SUCCESS) { return err_code; } uart_uuid.type = p_ble_nus_c->uuid_type; uart_uuid.uuid = BLE_UUID_NUS_SERVICE; // save the pointer to the ble_uart_c_t struct locally mp_ble_nus_c = p_ble_nus_c; p_ble_nus_c->conn_handle = BLE_CONN_HANDLE_INVALID; p_ble_nus_c->evt_handler = p_ble_nus_c_init->evt_handler; p_ble_nus_c->nus_rx_handle = BLE_GATT_HANDLE_INVALID; p_ble_nus_c->nus_tx_handle = BLE_GATT_HANDLE_INVALID; return ble_db_discovery_evt_register(&uart_uuid, db_discover_evt_handler);}串口服务回调函数可以看到对应的事件类型的处理，因为串口服务只有2个特征值，一个notify（通知） 和一个write and write no response（写并无返回）的属性
这里在描述对应事件的时候就会产生对应的事件，比如扫描的时候发现了write and write no response（BLE_NUS_C_EVT_FOUND_NUS_TX_CHARACTERISTIC）的特征值就是跳到BLE_NUS_C_EVT_FOUND_NUS_TX_CHARACTERISTIC事件，
扫描到notify（BLE_NUS_C_EVT_FOUND_NUS_RX_CHARACTERISTIC）的事件，主机要使能从机，这样才能接到从机主动发来的信息，
BLE_NUS_C_EVT_NUS_RX_EVT 事件是，当使能了从机，从机发送过来信息的时候产生的事件，
BLE_NUS_C_EVT_DISCONNECTED ,蓝牙断开事件，断开从新开始扫描
<pre name="code" class="cpp">/**@snippet [Handling events from the ble_nus_c module] */ static void ble_nus_c_evt_handler(ble_nus_c_t * p_ble_nus_c, const ble_nus_c_evt_t * p_ble_nus_evt){ uint32_t err_code; switch (p_ble_nus_evt->evt_type) { case BLE_NUS_C_EVT_FOUND_NUS_TX_CHARACTERISTIC: APPL_LOG("The device has the device TX characteristic\r\n"); break; case BLE_NUS_C_EVT_FOUND_NUS_RX_CHARACTERISTIC: err_code = ble_nus_c_rx_notif_enable(p_ble_nus_c); APP_ERROR_CHECK(err_code); APPL_LOG("The device has the device RX characteristic\r\n"); break; case BLE_NUS_C_EVT_NUS_RX_EVT: for (uint32_t i = 0; i < p_ble_nus_evt->data_len; i++) { while(app_uart_put( p_ble_nus_evt->p_data[i]) != NRF_SUCCESS); } break; case BLE_NUS_C_EVT_DISCONNECTED: APPL_LOG("NUS device disconnected\r\n"); scan_start(); break; }}开始扫描主要是扫描参数的设置。
<pre name="code" class="cpp">#define SCAN_INTERVAL 0x00A0 /**< Determines scan interval in units of 0.625 millisecond. */#define SCAN_WINDOW 0x0050 /**< Determines scan window in units of 0.625 millisecond. */#define SCAN_ACTIVE 1 /**< If 1, performe active scanning (scan requests). */#define SCAN_SELECTIVE 0 /**< If 1, ignore unknown devices (non whitelisted). */#define SCAN_TIMEOUT 0x0000
/** * @brief Parameters used when scanning. */static const ble_gap_scan_params_t m_scan_params = { .active = SCAN_ACTIVE, .selective = SCAN_SELECTIVE, .p_whitelist = NULL, .interval = SCAN_INTERVAL, .window = SCAN_WINDOW, .timeout = SCAN_TIMEOUT };/**@brief Function to start scanning. */static void scan_start(void){ uint32_t err_code; err_code = sd_ble_gap_scan_start(&m_scan_params); APP_ERROR_CHECK(err_code); err_code = bsp_indication_set(BSP_INDICATE_SCANNING); APP_ERROR_CHECK(err_code);}开始扫描后如果发现了广播数据，就会产生广播报告事件。即BLE_GAP_EVT_ADV_REPORT事件，然后在通过is_uuid_present() 函数来找对应的是UUID以及类型，通过这2个特征来识别是不是要连接的从机，然后通过sd_ble_gap_connect来连接从机，连接是通过mac地址来连接的如下
err_code = sd_ble_gap_connect(&p_adv_report->peer_addr,
&m_scan_params,
&m_connection_param);
当连接上了蓝牙产生，BLE_GAP_EVT_CONNECTED事件，在这里，
开始发现服务和特征值：ble_db_discovery_start(&m_ble_db_discovery, p_ble_evt->evt.gap_evt.conn_handle);具体代码如下:
/**@brief Function for dispatching a BLE stack event to all modules with a BLE stack event handler. * * @details This function is called from the scheduler in the main loop after a BLE stack event has * been received. * * @param[in] p_ble_evt Bluetooth stack event. */static void ble_evt_dispatch(ble_evt_t * p_ble_evt){ on_ble_evt(p_ble_evt); bsp_btn_ble_on_ble_evt(p_ble_evt); ble_db_discovery_on_ble_evt(&m_ble_db_discovery, p_ble_evt); ble_nus_c_on_ble_evt(&m_ble_nus_c,p_ble_evt);}/**@brief Function for handling the Application's BLE Stack events. * * @param[in] p_ble_evt Bluetooth stack event. */static void on_ble_evt(ble_evt_t * p_ble_evt){ uint32_t err_code; const ble_gap_evt_t * p_gap_evt = &p_ble_evt->evt.gap_evt; switch (p_ble_evt->header.evt_id) { case BLE_GAP_EVT_ADV_REPORT: { const ble_gap_evt_adv_report_t *p_adv_report = &p_gap_evt->params.adv_report; if (is_uuid_present(&m_nus_uuid, p_adv_report)) { err_code = sd_ble_gap_connect(&p_adv_report->peer_addr, &m_scan_params, &m_connection_param); if (err_code == NRF_SUCCESS) { // scan is automatically stopped by the connect err_code = bsp_indication_set(BSP_INDICATE_IDLE); APP_ERROR_CHECK(err_code); APPL_LOG("Connecting to target %02x%02x%02x%02x%02x%02x\r\n", p_adv_report->peer_addr.addr[0], p_adv_report->peer_addr.addr[1], p_adv_report->peer_addr.addr[2], p_adv_report->peer_addr.addr[3], p_adv_report->peer_addr.addr[4], p_adv_report->peer_addr.addr[5] ); } } break; } case BLE_GAP_EVT_CONNECTED: APPL_LOG("Connected to target\r\n"); err_code = bsp_indication_set(BSP_INDICATE_CONNECTED); APP_ERROR_CHECK(err_code); m_ble_nus_c.conn_handle = p_ble_evt->evt.gap_evt.conn_handle; // start discovery of services. The NUS Client waits for a discovery result err_code = ble_db_discovery_start(&m_ble_db_discovery, p_ble_evt->evt.gap_evt.conn_handle); APP_ERROR_CHECK(err_code); break; case BLE_GAP_EVT_TIMEOUT: if (p_gap_evt->params.timeout.src == BLE_GAP_TIMEOUT_SRC_SCAN) { APPL_LOG("[APPL]: Scan timed out.\r\n"); scan_start(); } else if (p_gap_evt->params.timeout.src == BLE_GAP_TIMEOUT_SRC_CONN) { APPL_LOG("[APPL]: Connection Request timed out.\r\n"); } break; case BLE_GAP_EVT_SEC_PARAMS_REQUEST: // Pairing not supported err_code = sd_ble_gap_sec_params_reply(p_ble_evt->evt.gap_evt.conn_handle, BLE_GAP_SEC_STATUS_PAIRING_NOT_SUPP, NULL, NULL); APP_ERROR_CHECK(err_code); break; case BLE_GAP_EVT_CONN_PARAM_UPDATE_REQUEST: // Accepting parameters requested by peer. err_code = sd_ble_gap_conn_param_update(p_gap_evt->conn_handle, &p_gap_evt->params.conn_param_update_request.conn_params); APP_ERROR_CHECK(err_code); break; default: break; }}开始发现服务，也会产生对应的事件，代码如下：第一次扫描发现的是主服务：产生的是BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP事件。表示找到了主服务
void ble_db_discovery_on_ble_evt(ble_db_discovery_t * const p_db_discovery, const ble_evt_t * const p_ble_evt){ if ((p_db_discovery == NULL) || (p_ble_evt == NULL)) { // Null pointer provided. Return. return; } if (!m_initialized) { return; } switch (p_ble_evt->header.evt_id) { case BLE_GAP_EVT_CONNECTED:SEGGER_RTT_printf(0,"BLE_GAP_EVT_CONNECTED\r\n"); p_db_discovery->conn_handle = p_ble_evt->evt.gap_evt.conn_handle; break; case BLE_GAP_EVT_DISCONNECTED: memset(p_db_discovery, 0, sizeof(ble_db_discovery_t)); p_db_discovery->conn_handle = BLE_CONN_HANDLE_INVALID; break; case BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP: <strong>//找到了主服务</strong>SEGGER_RTT_printf(0,"BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP\r\n"); on_primary_srv_discovery_rsp(p_db_discovery, &(p_ble_evt->evt.gattc_evt)); break; case BLE_GATTC_EVT_CHAR_DISC_RSP: SEGGER_RTT_printf(0,"BLE_GATTC_EVT_CHAR_DISC_RSP\r\n"); on_characteristic_discovery_rsp(p_db_discovery, &(p_ble_evt->evt.gattc_evt)); break; case BLE_GATTC_EVT_DESC_DISC_RSP:SEGGER_RTT_printf(0,"BLE_GATTC_EVT_DESC_DISC_RSP\r\n"); //SEGGER_RTT_printf(0,"\r\np_ble_evt->header.evt_id=%d\r\n,p_ble_evt->header.evt_id"); on_descriptor_discovery_rsp(p_db_discovery, &(p_ble_evt->evt.gattc_evt)); break; default: break; }}这里是发现主服务之后的处理，找特征值：characteristics_discover(p_db_discovery);
static void on_primary_srv_discovery_rsp(ble_db_discovery_t * const p_db_discovery, const ble_gattc_evt_t * const p_ble_gattc_evt){ if (p_ble_gattc_evt->gatt_status == BLE_GATT_STATUS_SUCCESS) { uint32_t err_code; const ble_gattc_evt_prim_srvc_disc_rsp_t * p_prim_srvc_disc_rsp_evt; ble_gatt_db_srv_t * p_srv_being_discovered; p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]); p_prim_srvc_disc_rsp_evt = &(p_ble_gattc_evt->params.prim_srvc_disc_rsp); p_srv_being_discovered->srv_uuid = p_prim_srvc_disc_rsp_evt->services[0].uuid; p_srv_being_discovered->handle_range = p_prim_srvc_disc_rsp_evt->services[0].handle_range; err_code = characteristics_discover(p_db_discovery); if (err_code != NRF_SUCCESS) { p_db_discovery->discovery_in_progress = false; // Error with discovering the service. // Indicate the error to the registered user application. discovery_error_evt_trigger(p_db_discovery, err_code); } } else { // Trigger Service Not Found event to the application. discovery_complete_evt_trigger(p_db_discovery, false); on_srv_disc_completion(p_db_discovery); }} if (
!is_char_discovery_reqd(p_db_discovery, p_last_known_char) ||
(p_srv_being_discovered->char_count == BLE_GATT_DB_MAX_CHARS)
)
{
perform_desc_discov = true;
}
判断是否找全了特征值，或者是否超出了设置的特征值的数量，BLE_GATT_DB_MAX_CHARS是预定义的一个特征值的个数，意思就是，假如一个服务里面有超过BLE_GATT_DB_MAX_CHARS特征值，则认为是全部找到了。可以在项目中适当的改变这个值的大小。
当全部找到了特征值，则descriptors_discover(p_db_discovery, &raise_discov_complete); 找描述符
static void on_characteristic_discovery_rsp(ble_db_discovery_t * const p_db_discovery, const ble_gattc_evt_t * const p_ble_gattc_evt){ uint32_t err_code; ble_gatt_db_srv_t * p_srv_being_discovered; bool perform_desc_discov = false; p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]); if (p_ble_gattc_evt->gatt_status == BLE_GATT_STATUS_SUCCESS) { const ble_gattc_evt_char_disc_rsp_t * p_char_disc_rsp_evt; p_char_disc_rsp_evt = &(p_ble_gattc_evt->params.char_disc_rsp); // Find out the number of characteristics that were previously discovered (in earlier // characteristic discovery responses, if any). uint8_t num_chars_prev_disc = p_srv_being_discovered->char_count; // Find out the number of characteristics that are currently discovered (in the // characteristic discovery response being handled). uint8_t num_chars_curr_disc = p_char_disc_rsp_evt->count; // Check if the total number of discovered characteristics are supported by this module. if ((num_chars_prev_disc + num_chars_curr_disc) <= BLE_GATT_DB_MAX_CHARS) { // Update the characteristics count. p_srv_being_discovered->char_count += num_chars_curr_disc; } else { // The number of characteristics discovered at the peer is more than the supported // maximum. This module will store only the characteristics found up to this point. p_srv_being_discovered->char_count = BLE_GATT_DB_MAX_CHARS; } uint32_t i; uint32_t j; for (i = num_chars_prev_disc, j = 0; i < p_srv_being_discovered->char_count; i++, j++) { p_srv_being_discovered->charateristics[i].characteristic = p_char_disc_rsp_evt->chars[j]; p_srv_being_discovered->charateristics[i].cccd_handle = BLE_GATT_HANDLE_INVALID; } ble_gattc_char_t * p_last_known_char; p_last_known_char = &(p_srv_being_discovered->charateristics[i - 1].characteristic); // If no more characteristic discovery is required, or if the maximum number of supported // characteristic per service has been reached, descriptor discovery will be performed. if ( !is_char_discovery_reqd(p_db_discovery, p_last_known_char) || (p_srv_being_discovered->char_count == BLE_GATT_DB_MAX_CHARS) ) { perform_desc_discov = true; } else { // Update the current characteristic index. p_db_discovery->curr_char_ind = p_srv_being_discovered->char_count; // Perform another round of characteristic discovery. err_code = characteristics_discover(p_db_discovery); <strong> //找特征值</strong> if (err_code != NRF_SUCCESS) { p_db_discovery->discovery_in_progress = false; discovery_error_evt_trigger(p_db_discovery, err_code); return; } } } else { // The previous characteristic discovery resulted in no characteristics. // descriptor discovery should be performed. perform_desc_discov = true; } if (perform_desc_discov) { bool raise_discov_complete; p_db_discovery->curr_char_ind = 0; err_code = descriptors_discover(p_db_discovery, &raise_discov_complete); <strong>//找描述符</strong> if (err_code != NRF_SUCCESS) { p_db_discovery->discovery_in_progress = false; discovery_error_evt_trigger(p_db_discovery, err_code); return; } if (raise_discov_complete) { // No more characteristics and descriptors need to be discovered. Discovery is complete. // Send a discovery complete event to the user application. DB_LOG("[DB]: Discovery of service with UUID 0x%x completed with success for Connection" " handle %d\r\n", p_srv_being_discovered->srv_uuid.uuid, p_db_discovery->conn_handle); discovery_complete_evt_trigger(p_db_discovery, true); on_srv_disc_completion(p_db_discovery); } }}找到了描述符则会产生BLE_GATTC_EVT_DESC_DISC_RSP事件，如果没有找全 则descriptors_discover(p_db_discovery, &raise_discov_complete);，再次发现描述符，并再次产生BLE_GATTC_EVT_DESC_DISC_RSP事件，如果全部找到了则 discovery_complete_evt_trigger(p_db_discovery, true);
/**@brief Function for handling descriptor discovery response. * * @param[in] p_db_discovery Pointer to the DB Discovery structure. * @param[in] p_ble_gattc_evt Pointer to the GATT Client event. */static void on_descriptor_discovery_rsp(ble_db_discovery_t * const p_db_discovery, const ble_gattc_evt_t * const p_ble_gattc_evt){ const ble_gattc_evt_desc_disc_rsp_t * p_desc_disc_rsp_evt; ble_gatt_db_srv_t * p_srv_being_discovered; p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]); p_desc_disc_rsp_evt = &(p_ble_gattc_evt->params.desc_disc_rsp); ble_gatt_db_char_t * p_char_being_discovered = &(p_srv_being_discovered->charateristics[p_db_discovery->curr_char_ind]); if (p_ble_gattc_evt->gatt_status == BLE_GATT_STATUS_SUCCESS) { // The descriptor was found at the peer. // If the descriptor was a CCCD, then the cccd_handle needs to be populated. uint32_t i; // Loop through all the descriptors to find the CCCD. for (i = 0; i < p_desc_disc_rsp_evt->count; i++) { if ( p_desc_disc_rsp_evt->descs[i].uuid.uuid == BLE_UUID_DESCRIPTOR_CLIENT_CHAR_CONFIG ) { p_char_being_discovered->cccd_handle = p_desc_disc_rsp_evt->descs[i].handle; break; } } } bool raise_discov_complete = false; if ((p_db_discovery->curr_char_ind + 1) == p_srv_being_discovered->char_count) { // No more characteristics and descriptors need to be discovered. Discovery is complete. // Send a discovery complete event to the user application. raise_discov_complete = true; } else { // Begin discovery of descriptors for the next characteristic. uint32_t err_code; p_db_discovery->curr_char_ind++; err_code = descriptors_discover(p_db_discovery, &raise_discov_complete); if (err_code != NRF_SUCCESS) { p_db_discovery->discovery_in_progress = false; // Error with discovering the service. // Indicate the error to the registered user application. discovery_error_evt_trigger(p_db_discovery, err_code); return; } } if (raise_discov_complete) { DB_LOG("[DB]: Discovery of service with UUID 0x%x completed with success for Connection" "handle %d\r\n", p_srv_being_discovered->srv_uuid.uuid, p_db_discovery->conn_handle); SEGGER_RTT_printf(0,"Discovery\r\n"); discovery_complete_evt_trigger(p_db_discovery, true); on_srv_disc_completion(p_db_discovery); }}现在来具体分析下这个函数：
首先找到对应的回调函数p_evt_handler = registered_handler_get(&(p_srv_being_discovered->srv_uuid));
nus_c_init(); ---> ble_nus_c_init(&m_ble_nus_c, &nus_c_init_t);-->ble_db_discovery_evt_register(&uart_uuid, db_discover_evt_handler);--->registered_handler_set(p_uuid, evt_handler);
static uint32_t registered_handler_set(const ble_uuid_t * const p_srv_uuid,
ble_db_discovery_evt_handler_t p_evt_handler)
{
if (m_num_of_handlers_reg < DB_DISCOVERY_MAX_USERS)
{
m_registered_handlers[m_num_of_handlers_reg].srv_uuid = *p_srv_uuid;
m_registered_handlers[m_num_of_handlers_reg].evt_handler = p_evt_handler;
m_num_of_handlers_reg++;
return NRF_SUCCESS;
}
else
{
return NRF_ERROR_NO_MEM;
}
}
通过一层一层，把串口的服务的类型 和回调函数复制给了m_registered_handlers结构体保存期来了，如果还有其他的服务也可以按照同样步骤添加。
最后把static void db_discover_evt_handler(ble_db_discovery_evt_t * p_evt)函数地址保存在m_registered_handlers里面了
再看
static ble_db_discovery_evt_handler_t registered_handler_get(ble_uuid_t * p_srv_uuid)
{
uint32_t i;
for (i = 0; i < m_num_of_handlers_reg; i++)
{
if (BLE_UUID_EQ(&(m_registered_handlers[i].srv_uuid), p_srv_uuid))
{
return (m_registered_handlers[i].evt_handler);
}
}
return NULL;
}
这里就是把输入的UUID的类型和m_registered_handlers保存的UUID的类型对比，如果一样则返回它对应的回调函数。
然后在m_pending_user_evts结构体赋值。因为is_srv_found == true
if (is_srv_found)
{
m_pending_user_evts[m_pending_usr_evt_index].evt.evt_type =
BLE_DB_DISCOVERY_COMPLETE;
m_pending_user_evts[m_pending_usr_evt_index].evt.params.discovered_db =
*p_srv_being_discovered;
}
最后执行, pending_user_evts_send();
/**@brief Function for sending all pending discovery events to the corresponding user modules.
*/
static void pending_user_evts_send(void)
{
uint32_t i;
for (i = 0; i < m_num_of_handlers_reg; i++)
{
// Pass the event to the corresponding event handler.
m_pending_user_evts[i].evt_handler(&(m_pending_user_evts[i].evt));
}
m_pending_usr_evt_index = 0;
}
在discovery_complete_evt_trigger里面
p_evt_handler = registered_handler_get(&(p_srv_being_discovered->srv_uuid)); ------> m_pending_user_evts[m_pending_usr_evt_index].evt_handler = p_evt_handler; // 把回调函数赋值给m_pending_user_evts对应的地址。
m_pending_user_evts[m_pending_usr_evt_index].evt.evt_type = BLE_DB_DISCOVERY_COMPLETE;
这样就执行了db_discover_evt_handler(ble_db_discovery_evt_t * p_evt)函数
static void discovery_complete_evt_trigger(ble_db_discovery_t * const p_db_discovery, bool is_srv_found){ ble_db_discovery_evt_handler_t p_evt_handler; ble_gatt_db_srv_t * p_srv_being_discovered; p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]); p_evt_handler = registered_handler_get(&(p_srv_being_discovered->srv_uuid)); if (p_evt_handler != NULL) { if (m_pending_usr_evt_index < DB_DISCOVERY_MAX_USERS) { // Insert an event into the pending event list. m_pending_user_evts[m_pending_usr_evt_index].evt.conn_handle = p_db_discovery->conn_handle; if (is_srv_found) { m_pending_user_evts[m_pending_usr_evt_index].evt.evt_type = BLE_DB_DISCOVERY_COMPLETE; m_pending_user_evts[m_pending_usr_evt_index].evt.params.discovered_db = *p_srv_being_discovered; } else { m_pending_user_evts[m_pending_usr_evt_index].evt.evt_type = BLE_DB_DISCOVERY_SRV_NOT_FOUND; } m_pending_user_evts[m_pending_usr_evt_index].evt_handler = p_evt_handler; m_pending_usr_evt_index++; if (m_pending_usr_evt_index == m_num_of_handlers_reg) { // All registered modules have pending events. Send all pending events to the user // modules. pending_user_evts_send(); } else { // Too many events pending. Do nothing. (Ideally this should not happen.) } } }}这里会把发现的特征值全部过一遍，然后执行对应的处理。执行对应的回调
经过 nus_c_init（）---> ble_nus_c_init(); 执行 ，把 ble_nus_c_evt_handler函数地址赋值给了mp_ble_nus_c.evt_handler
所以mp_ble_nus_c->evt_handler 就是 ble_nus_c_evt_handler。
p_evt就发现一个服务的全部信息的结构体，比如主服务的UUID，特征值的UUID一个权限，handle，发现特征值的个数（p_evt->params.discovered_db.char_count）等等，因为串口有2个特征值，write和notify 对应BLE_UUID_NUS_TX_CHARACTERISTIC和BLE_UUID_NUS_RX_CHARACTERISTIC 2个UUID，所以只要在找到对应的uuid，并保存下handle就好了。（假如提前并不知道对方的属性呢？）
注意：为什么这里要保存handle，因为当主机发送要发数据给从机的时候，比如有好几个特征值，要往某个特定的UUID发送数据，就必须知道地址，而handle就是类是地址，每个特征值对应的地址，当主机连上从机后，知道了handle就可以往特定的权限的UUID通信了。
static void db_discover_evt_handler(ble_db_discovery_evt_t * p_evt){ // Check if the NUS was discovered. if (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE && p_evt->params.discovered_db.srv_uuid.uuid == BLE_UUID_NUS_SERVICE && p_evt->params.discovered_db.srv_uuid.type == mp_ble_nus_c->uuid_type) { uint32_t i; for (i = 0; i < p_evt->params.discovered_db.char_count; i++) { if (p_evt->params.discovered_db.charateristics[i].characteristic.uuid.uuid == BLE_UUID_NUS_TX_CHARACTERISTIC) { mp_ble_nus_c->nus_tx_handle = p_evt->params.discovered_db.charateristics[i].characteristic.handle_value; if (mp_ble_nus_c->evt_handler != NULL) { ble_nus_c_evt_t nus_c_evt; nus_c_evt.evt_type = BLE_NUS_C_EVT_FOUND_NUS_TX_CHARACTERISTIC; mp_ble_nus_c->evt_handler(mp_ble_nus_c, &nus_c_evt); } } else if (p_evt->params.discovered_db.charateristics[i].characteristic.uuid.uuid == BLE_UUID_NUS_RX_CHARACTERISTIC) { mp_ble_nus_c->nus_rx_handle = p_evt->params.discovered_db.charateristics[i].characteristic.handle_value; mp_ble_nus_c->nus_rx_cccd_handle = p_evt->params.discovered_db.charateristics[i].cccd_handle; if (mp_ble_nus_c->evt_handler != NULL) { ble_nus_c_evt_t nus_c_evt; nus_c_evt.evt_type = BLE_NUS_C_EVT_FOUND_NUS_RX_CHARACTERISTIC; mp_ble_nus_c->evt_handler(mp_ble_nus_c, &nus_c_evt); } } } }}接下看对应的事件会对应对的case 事件。这里看 BLE_NUS_C_EVT_FOUND_NUS_RX_CHARACTERISTIC 事件。这事件表示特征值的属性为notify 所以要使能监听才能收到数据，使能操作ble_nus_c_rx_notif_enable(p_ble_nus_c);
BLE_NUS_C_EVT_NUS_RX_EVT为接收从机发送数据事件。
/**@snippet [Handling events from the ble_nus_c module] */ static void ble_nus_c_evt_handler(ble_nus_c_t * p_ble_nus_c, const ble_nus_c_evt_t * p_ble_nus_evt){ uint32_t err_code; switch (p_ble_nus_evt->evt_type) { case BLE_NUS_C_EVT_FOUND_NUS_TX_CHARACTERISTIC: APPL_LOG("The device has the device TX characteristic\r\n"); break; case BLE_NUS_C_EVT_FOUND_NUS_RX_CHARACTERISTIC: err_code = ble_nus_c_rx_notif_enable(p_ble_nus_c); APP_ERROR_CHECK(err_code); APPL_LOG("The device has the device RX characteristic\r\n"); break; case BLE_NUS_C_EVT_NUS_RX_EVT: for (uint32_t i = 0; i < p_ble_nus_evt->data_len; i++) { while(app_uart_put( p_ble_nus_evt->p_data[i]) != NRF_SUCCESS); } break; case BLE_NUS_C_EVT_DISCONNECTED: APPL_LOG("NUS device disconnected\r\n"); scan_start(); break; }}好了 到现在大概分析完了程序执行的流程。。。。。。上一张图对应ble_db_discovery_on_ble_evt（）函数，执行流程
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