Android 上面的蓝牙inquiry 是在设置界面，打开蓝牙就会自动搜索周边的蓝牙设备，其最终调用到协议栈的start_discovery接口，此篇文章分析该接口的调用流程以及与controller交互过程。

static int start_discovery(void)
{/*sanity check*/if (interface_ready() ==FALSE)returnBT_STATUS_NOT_READY;return btif_dm_start_discovery();
}

bt_status_t btif_dm_start_discovery(void)
{tBTA_DM_INQ inq_params;tBTA_SERVICE_MASK services= 0;tBTA_DM_BLE_PF_FILT_PARAMS adv_filt_param;#if (defined(BLE_INCLUDED) && (BLE_INCLUDED == TRUE))memset(&adv_filt_param, 0, sizeof(tBTA_DM_BLE_PF_FILT_PARAMS));/*Cleanup anything remaining on index 0*/BTA_DmBleScanFilterSetup(BTA_DM_BLE_SCAN_COND_DELETE,0, &adv_filt_param, NULL,bte_scan_filt_param_cfg_evt,0);/*Add an allow-all filter on index 0*/adv_filt_param.dely_mode=IMMEDIATE_DELY_MODE;adv_filt_param.feat_seln=ALLOW_ALL_FILTER;adv_filt_param.filt_logic_type=BTA_DM_BLE_PF_FILT_LOGIC_OR;adv_filt_param.list_logic_type=BTA_DM_BLE_PF_LIST_LOGIC_OR;adv_filt_param.rssi_low_thres=LOWEST_RSSI_VALUE;adv_filt_param.rssi_high_thres=LOWEST_RSSI_VALUE;BTA_DmBleScanFilterSetup(BTA_DM_BLE_SCAN_COND_ADD,0, &adv_filt_param, NULL,bte_scan_filt_param_cfg_evt,0);/*TODO: Do we need to handle multiple inquiries at the same time?*//*Set inquiry params and call API*/inq_params.mode= BTA_DM_GENERAL_INQUIRY|BTA_BLE_GENERAL_INQUIRY;//设置inquiry模式，ble和bredr
#elseinq_params.mode=BTA_DM_GENERAL_INQUIRY;#endifinq_params.duration= BTIF_DM_DEFAULT_INQ_MAX_DURATION;//设置超时时间
inq_params.max_resps= BTIF_DM_DEFAULT_INQ_MAX_RESULTS;//设置接收的最大的response数量inq_params.report_dup =TRUE;inq_params.filter_type= BTA_DM_INQ_CLR;//0/*TODO: Filter device by BDA needs to be implemented here*//*Will be enabled to TRUE once inquiry busy level has been received*/btif_dm_inquiry_in_progress=FALSE;/*find nearby devices*/BTA_DmSearch(&inq_params, services, bte_search_devices_evt);//执行搜索returnBT_STATUS_SUCCESS;
}

上面代码的主要做的事情是，设置相关的搜索的参数，然后调用BTA_DmSearch(&inq_params, services, bte_search_devices_evt); 进行搜索。

我们这里再次整理一下 传入BTA_DmSearch的参数：

    inq_params.mode = BTA_DM_GENERAL_INQUIRY|BTA_BLE_GENERAL_INQUIRY;inq_params.duration=BTIF_DM_DEFAULT_INQ_MAX_DURATION;inq_params.max_resps=BTIF_DM_DEFAULT_INQ_MAX_RESULTS;inq_params.report_dup=TRUE;inq_params.filter_type= BTA_DM_INQ_CLR;//0
tBTA_SERVICE_MASK services= 0;bte_search_devices_evt 是一个回调函数，实现也是在btif_dm.c，最终会被赋值给bta_dm_search_cb.p_search_cback= bte_search_devices_evt

我们看看BTA_DmSearch具体的实现，

/*******************************************************************************
**
** Function         BTA_DmSearch
**
** Description      This function searches for peer Bluetooth devices. It performs
**                  an inquiry and gets the remote name for devices. Service
**                  discovery is done if services is non zero
**
**
** Returns          void
**
*******************************************************************************/
void BTA_DmSearch(tBTA_DM_INQ *p_dm_inq, tBTA_SERVICE_MASK services, tBTA_DM_SEARCH_CBACK *p_cback)
{tBTA_DM_API_SEARCH*p_msg;if ((p_msg = (tBTA_DM_API_SEARCH *) GKI_getbuf(sizeof(tBTA_DM_API_SEARCH))) !=NULL){memset(p_msg,0, sizeof(tBTA_DM_API_SEARCH));p_msg->hdr.event =BTA_DM_API_SEARCH_EVT;memcpy(&p_msg->inq_params, p_dm_inq, sizeof(tBTA_DM_INQ));p_msg->services =services;p_msg->p_cback =p_cback;p_msg->rs_res  =BTA_DM_RS_NONE;bta_sys_sendmsg(p_msg);}}

这里发现就是组装了一个msg，然后发送给btu 线程处理，这里整理一下发送给btu 线程的参数：

p_msg->hdr.event = BTA_DM_API_SEARCH_EVT;
memcpy(&p_msg->inq_params, p_dm_inq, sizeof(tBTA_DM_INQ)); 上面赋值的参数
p_msg->services = services;//service = 0
p_msg->p_cback = p_cback;//bte_search_devices_evt

p_msg->rs_res = BTA_DM_RS_NONE;

我们查找一下， BTA_DM_API_SEARCH_EVT 执行的函数：bta_dm_search_start

/*******************************************************************************
**
** Function         bta_dm_search_start
**
** Description      Starts an inquiry
**
**
** Returns          void
**
*******************************************************************************/
void bta_dm_search_start (tBTA_DM_MSG *p_data)
{tBTM_INQUIRY_CMPL result;#if (BLE_INCLUDED == TRUE && BTA_GATT_INCLUDED == TRUE)UINT16 len= (UINT16)(sizeof(tBT_UUID) * p_data->search.num_uuid);bta_dm_gattc_register();#endifif (p_bta_dm_cfg->avoid_scatter &&(p_data->search.rs_res == BTA_DM_RS_NONE) &&bta_dm_check_av(BTA_DM_API_SEARCH_EVT)){memcpy(&bta_dm_cb.search_msg, &p_data->search, sizeof(tBTA_DM_API_SEARCH));return;}BTM_ClearInqDb(NULL);/*save search params*/bta_dm_search_cb.p_search_cback= p_data->search.p_cback;bta_dm_search_cb.services= p_data->search.services;#if (BLE_INCLUDED == TRUE && BTA_GATT_INCLUDED == TRUE)utl_freebuf((void **)&bta_dm_search_cb.p_srvc_uuid);if ((bta_dm_search_cb.num_uuid = p_data->search.num_uuid) != 0 &&p_data->search.p_uuid != NULL)//如果在搜索的时候设置了uuid，那么也会将这个值copy给bta_dm_search_cb.p_srvc_uuid
{bta_dm_search_cb.p_srvc_uuid= (tBT_UUID *)GKI_getbuf(len)memcpy(bta_dm_search_cb.p_srvc_uuid, p_data->search.p_uuid, len);}#endifresult.status= BTM_StartInquiry(   (tBTM_INQ_PARMS*)&p_data->search.inq_params,bta_dm_inq_results_cb,//扫描到设备调用此函数(tBTM_CMPL_CB*) bta_dm_inq_cmpl_cb);//扫描完成会调用到此函数if (result.status !=BTM_CMD_STARTED){result.num_resp= 0;bta_dm_inq_cmpl_cb ((void *)&result);//如果开始失败，直接调用回调函数汇报
}
}

上面的代码执行完，我们看看bta_dm_search_cb的各个结构的值：

bta_dm_search_cb.p_search_cback = bte_search_devices_evt

bta_dm_search_cb.services = 0；

bta_dm_search_cb.num_uuid  =0；

bta_dm_search_cb.p_srvc_uuid = NULL;

下面继续看看BTM_StartInquiry 的实现，这里可以简单分析一下，传入的三个参数：

第一个参数是，上面组装的inquiry相关的设置。

第二个参数是 扫描到设备调用

第三个参数是 扫描完成 （inquiry complete）的时候调用

/*******************************************************************************
**
** Function         BTM_StartInquiry
**
** Description      This function is called to start an inquiry.
**
** Parameters:      p_inqparms - pointer to the inquiry information
**                      mode - GENERAL or LIMITED inquiry, BR/LE bit mask seperately
**                      duration - length in 1.28 sec intervals (If '0', the inquiry is CANCELLED)
**                      max_resps - maximum amount of devices to search for before ending the inquiry
**                      filter_cond_type - BTM_CLR_INQUIRY_FILTER, BTM_FILTER_COND_DEVICE_CLASS, or
**                                         BTM_FILTER_COND_BD_ADDR
**                      filter_cond - value for the filter (based on filter_cond_type)
**
**                  p_results_cb   - Pointer to the callback routine which gets called
**                                upon receipt of an inquiry result. If this field is
**                                NULL, the application is not notified.
**
**                  p_cmpl_cb   - Pointer to the callback routine which gets called
**                                upon completion.  If this field is NULL, the
**                                application is not notified when completed.
** Returns          tBTM_STATUS
**                  BTM_CMD_STARTED if successfully initiated
**                  BTM_BUSY if already in progress
**                  BTM_ILLEGAL_VALUE if parameter(s) are out of range
**                  BTM_NO_RESOURCES if could not allocate resources to start the command
**                  BTM_WRONG_MODE if the device is not up.
**
*******************************************************************************/tBTM_STATUS BTM_StartInquiry (tBTM_INQ_PARMS*p_inqparms, tBTM_INQ_RESULTS_CB *p_results_cb,tBTM_CMPL_CB*p_cmpl_cb)
{tBTM_STATUS  status=BTM_CMD_STARTED;tBTM_INQUIRY_VAR_ST*p_inq = &btm_cb.btm_inq_vars;p_inq->scan_type =INQ_GENERAL;
.../*Save the inquiry parameters to be used upon the completion of setting/clearing the inquiry filter*/p_inq->inqparms = *p_inqparms;//保存inquiry的参数/*Initialize the inquiry variables*/p_inq->state = BTM_INQ_ACTIVE_STATE;//activep_inq->p_inq_cmpl_cb =p_cmpl_cb;p_inq->p_inq_results_cb =p_results_cb;p_inq->inq_cmpl_info.num_resp = 0;         /*Clear the results counter*/p_inq->inq_active = p_inqparms->mode;//0x11/*start LE inquiry here if requested*/if ((p_inqparms->mode &BTM_BLE_INQUIRY_MASK)){if ((status = btm_ble_start_inquiry((UINT8)(p_inqparms->mode &BTM_BLE_INQUIRY_MASK),p_inqparms->duration)) !=BTM_CMD_STARTED){BTM_TRACE_ERROR("Err Starting LE Inquiry.");p_inq->inqparms.mode &= ~BTM_BLE_INQUIRY_MASK;}#if (!defined(BTA_HOST_INTERLEAVE_SEARCH) || BTA_HOST_INTERLEAVE_SEARCH == FALSE)p_inqparms->mode &= ~BTM_BLE_INQUIRY_MASK;//开始inquiry之后，mode参数置0
#endif}/*BR/EDR inquiry portion*/.../*Before beginning the inquiry the current filter must be cleared, so initiate the command*/if ((status = btm_set_inq_event_filter (p_inqparms->filter_cond_type,&p_inqparms->filter_cond)) != BTM_CMD_STARTED)//这里没有看到BRRDR的扫描，而只有这个清楚过滤的函数，那我可以想象，肯定是这个函数做完之后会自动开始bredr设备的inquiryp_inq->state =BTM_INQ_INACTIVE_STATE;return(status);
}

上面的代码主要做了三件事：

1. 将一些参数保存在tBTM_INQUIRY_VAR_ST *p_inq = &btm_cb.btm_inq_vars  这个结构。
   1. p_inq->scan_type = INQ_GENERAL;
   2. p_inq->inqparms = *p_inqparms;
   3. p_inq->state = BTM_INQ_ACTIVE_STATE;
   4. p_inq->p_inq_cmpl_cb = p_cmpl_cb;
   5. p_inq->p_inq_results_cb = p_results_cb;

   6. p_inq->inq_cmpl_info.num_resp = 0; /* Clear the results counter */

   7. p_inq->inq_active = p_inqparms->mode = 0x11（BLE|BREDR）
2. 做BLE 的inquiry ：btm_ble_start_inquiry((UINT8)(p_inqparms->mode & BTM_BLE_INQUIRY_MASK),p_inqparms->duration)
3. 做BREDR的inquiry：btm_set_inq_event_filter (p_inqparms->filter_cond_type,&p_inqparms->filter_cond)

btm_ble_start_inquiry

tBTM_STATUS btm_ble_start_inquiry (UINT8 mode, UINT8   duration)
{tBTM_STATUS status=BTM_CMD_STARTED;tBTM_BLE_CB*p_ble_cb = &btm_cb.ble_ctr_cb;tBTM_INQUIRY_VAR_ST*p_inq = &btm_cb.btm_inq_vars;
...if (!BTM_BLE_IS_SCAN_ACTIVE(p_ble_cb->scan_activity))//如果没有scan 正在进行，开始scan
{btsnd_hcic_ble_set_scan_params(BTM_BLE_SCAN_MODE_ACTI,//active scan
BTM_BLE_LOW_LATENCY_SCAN_INT,BTM_BLE_LOW_LATENCY_SCAN_WIN,btm_cb.ble_ctr_cb.addr_mgnt_cb.own_addr_type,SP_ADV_ALL);#if (defined BLE_PRIVACY_SPT && BLE_PRIVACY_SPT == TRUE)/*enable IRK list*/btm_ble_enable_resolving_list_for_platform(BTM_BLE_RL_SCAN);#endifp_ble_cb->inq_var.scan_duplicate_filter  =BTM_BLE_DUPLICATE_DISABLE;status= btm_ble_start_scan();//开始scan
}else if ((p_ble_cb->inq_var.scan_interval != BTM_BLE_LOW_LATENCY_SCAN_INT) ||(p_ble_cb->inq_var.scan_window != BTM_BLE_LOW_LATENCY_SCAN_WIN)) {//如果已经有正在scan的行为，先停掉当前的scan，启动新的scan
btsnd_hcic_ble_set_scan_enable(BTM_BLE_SCAN_DISABLE, BTM_BLE_DUPLICATE_ENABLE);btsnd_hcic_ble_set_scan_params(BTM_BLE_SCAN_MODE_ACTI,BTM_BLE_LOW_LATENCY_SCAN_INT,BTM_BLE_LOW_LATENCY_SCAN_WIN,btm_cb.ble_ctr_cb.addr_mgnt_cb.own_addr_type,SP_ADV_ALL);btsnd_hcic_ble_set_scan_enable(BTM_BLE_SCAN_ENABLE, BTM_BLE_DUPLICATE_DISABLE);}if (status ==BTM_CMD_STARTED){p_inq->inq_active |= mode;//置位p_ble_cb->scan_activity |=mode;if (duration != 0){/*start inquiry timer*/btu_start_timer (&p_inq->inq_timer_ent, BTU_TTYPE_BLE_INQUIRY, duration);//开始定时器，当定时器时间到的时候会 disable scan
}}returnstatus;
}

上面的代码的逻辑非常的简单，需要留意一下就是 p_inq->inq_active |= mode 和 p_ble_cb->scan_activity |= mode;

现在Ble 的扫描就开始了，持续时间10s = 10*1000ms，定时器超时时间到了之后会取消scan。

从上面我们还可以看出从inquiry 下发的ble scan的优先级还是很高，它会停掉当前的scan的行为。如果此时后台有observe 行为，也会被停掉。

btm_set_inq_event_filter

statictBTM_STATUS btm_set_inq_event_filter (UINT8 filter_cond_type,tBTM_INQ_FILT_COND*p_filt_cond)
{
...btm_cb.btm_inq_vars.inqfilt_active=TRUE;设置了标志位/*Filter the inquiry results for the specified condition type and value*/if(btsnd_hcic_set_event_filter(HCI_FILTER_INQUIRY_RESULT, filter_cond_type,p_cond, condition_length))return(BTM_CMD_STARTED);elsereturn(BTM_NO_RESOURCES);
}

上面主要是发送了HCI_FILTER_INQUIRY_RESULT ，以及设置了状态位：btm_cb.btm_inq_vars.inqfilt_active = TRUE

搜索的行为肯定是在这个函数的完成事件中进行的。

static void btu_hcif_hdl_command_complete (UINT16 opcode, UINT8 *p, UINT16 evt_len,void *p_cplt_cback)
{switch(opcode){caseHCI_INQUIRY_CANCEL:/*Tell inquiry processing that we are done*/btm_process_cancel_complete(HCI_SUCCESS, BTM_BR_INQUIRY_MASK);break;caseHCI_SET_EVENT_FILTER:btm_event_filter_complete (p);//执行此函数break;

void btm_event_filter_complete (UINT8 *p)
{UINT8            hci_status;tBTM_STATUS      status;tBTM_INQUIRY_VAR_ST*p_inq = &btm_cb.btm_inq_vars;tBTM_CMPL_CB*p_cb = p_inq->p_inqfilter_cmpl_cb;
.../*Only process the inquiry filter; Ignore the connection filter until itis used by the upper layers*/if (p_inq->inqfilt_active == TRUE ) //在命令下发的时候已经设置
{/*Extract the returned status from the buffer*/STREAM_TO_UINT8 (hci_status, p);if (hci_status !=HCI_SUCCESS){/*If standalone operation, return the error status; if embedded in the inquiry, continue the inquiry*/BTM_TRACE_WARNING ("BTM Warning: Set Event Filter Failed (HCI returned 0x%x)", hci_status);status=BTM_ERR_PROCESSING;}elsestatus=BTM_SUCCESS;/*If the set filter was initiated externally (via BTM_SetInqEventFilter), call thecallback function to notify the initiator that it has completed*/if (p_inq->state == BTM_INQ_INACTIVE_STATE)//此时是active状态
{p_inq->inqfilt_active =FALSE;if(p_cb)(*p_cb) (&status);}else    /*An inquiry is active (the set filter command was internally generated),process the next state of the process (Set a new filter or start the inquiry).*/{if(status !=BTM_SUCCESS){/*Process the inquiry complete (Error Status)*/btm_process_inq_complete (BTM_ERR_PROCESSING, (UINT8)(p_inq->inqparms.mode &BTM_BR_INQUIRY_MASK));/*btm_process_inq_complete() does not restore the following settings on periodic inquiry*/p_inq->inqfilt_active =FALSE;p_inq->inq_active =BTM_INQUIRY_INACTIVE;p_inq->state =BTM_INQ_INACTIVE_STATE;return;}/*Check to see if a new filter needs to be set up*/if (p_inq->state ==BTM_INQ_CLR_FILT_STATE){if ((status = btm_set_inq_event_filter (p_inq->inqparms.filter_cond_type, &p_inq->inqparms.filter_cond)) ==BTM_CMD_STARTED){p_inq->state =BTM_INQ_SET_FILT_STATE;}else    /*Error setting the filter: Call the initiator's callback function to indicate a failure*/{p_inq->inqfilt_active =FALSE;/*Process the inquiry complete (Error Status)*/btm_process_inq_complete (BTM_ERR_PROCESSING, (UINT8)(p_inq->inqparms.mode &BTM_BR_INQUIRY_MASK));}}else    /*Initiate the Inquiry or Periodic Inquiry*/{p_inq->state = BTM_INQ_ACTIVE_STATE;//处于该状态p_inq->inqfilt_active = FALSE;//设置falsebtm_initiate_inquiry (p_inq);//开始扫描
}}}
}

上面代码的做的主要的事情:

p_inq->state = BTM_INQ_ACTIVE_STATE;
p_inq->inqfilt_active = FALSE;
btm_initiate_inquiry (p_inq);

继续看btm_initiate_inquiry的实现：

static void btm_initiate_inquiry (tBTM_INQUIRY_VAR_ST *p_inq)
{const LAP       *lap;tBTM_INQ_PARMS*p_inqparms = &p_inq->inqparms;btm_acl_update_busy_level (BTM_BLI_INQ_EVT);
...lap= (p_inq->inq_active & BTM_LIMITED_INQUIRY_ACTIVE) ? &limited_inq_lap : &general_inq_lap;//设置LAP
{btm_clr_inq_result_flt();//清数据库/*Allocate memory to hold bd_addrs responding*/if ((p_inq->p_bd_db = (tINQ_BDADDR *)GKI_getbuf(GKI_MAX_BUF_SIZE)) !=NULL){p_inq->max_bd_entries = (UINT16)(GKI_MAX_BUF_SIZE / sizeof(tINQ_BDADDR));memset(p_inq->p_bd_db, 0, GKI_MAX_BUF_SIZE);/*BTM_TRACE_DEBUG("btm_initiate_inquiry: memory allocated for %d bdaddrs",p_inq->max_bd_entries);*/}if (!btsnd_hcic_inquiry(*lap, p_inqparms->duration, 0))//发送inquiry 命令btm_process_inq_complete (BTM_NO_RESOURCES, (UINT8)(p_inqparms->mode &BTM_BR_INQUIRY_MASK));}
}

上面代码中，重点就是btsnd_hcic_inquiry(*lap, p_inqparms->duration, 0)

其实现就是向controller 发送inquiry 的命令。这里注意其duration参数是10，对应的实际的值是10*1.28s,在12.8秒之后会有inquiry complete 事件传上来。

对于inquiry 的命令发送流程就分析到这里。