关于低功耗蓝牙的连接参数更新

首先要明确：连接参数是由主机端确定的，从机端可以发起更新连接参数的请求。主机端可以直接下发连接参数，而从机端则只能是发起更新请求并附带想要的连接参数范围。

在初始化中将想要的连接参数设置进osal( 在和iOS设备连接时需要注意一些规则，在前面有提到 ):

GAPRole_SetParameter( GAPROLE_PARAM_UPDATE_ENABLE, sizeof( uint8 ), &enable_update_request );
    GAPRole_SetParameter( GAPROLE_MIN_CONN_INTERVAL, sizeof( uint16 ), &desired_min_interval );
    GAPRole_SetParameter( GAPROLE_MAX_CONN_INTERVAL, sizeof( uint16 ), &desired_max_interval );
    GAPRole_SetParameter( GAPROLE_SLAVE_LATENCY, sizeof( uint16 ), &desired_slave_latency );
    GAPRole_SetParameter( GAPROLE_TIMEOUT_MULTIPLIER, sizeof( uint16 ), &desired_conn_timeout );
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追踪下GAPRole_SetParameter函数中这些参数的运作：

case GAPROLE_MIN_CONN_INTERVAL:
      {
        uint16 newInterval = *((uint16*)pValue);
        if (   len == sizeof ( uint16 )           &&
             ( newInterval >= MIN_CONN_INTERVAL ) &&
             ( newInterval <= MAX_CONN_INTERVAL ) )
        {
          gapRole_MinConnInterval = newInterval;
        }
        else
        {
          ret = bleInvalidRange;
        }
      }
      break;
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都是存储在全局变量中，那么这些参数是何时发出去的呢？
且看：
在建立连接后会产生一个MSG然后在gapRole_ProcessGAPMsg函数中的GAP_LINK_PARAM_UPDATE_EVENT事件
gap.h中有对这一事件的介绍

case GAP_LINK_ESTABLISHED_EVENT:
      {
        gapEstLinkReqEvent_t *pPkt = (gapEstLinkReqEvent_t *)pMsg;

        if ( pPkt->hdr.status == SUCCESS )
        {
          VOID osal_memcpy( gapRole_ConnectedDevAddr, pPkt->devAddr, B_ADDR_LEN );
          gapRole_ConnectionHandle = pPkt->connectionHandle;
          gapRole_state = GAPROLE_CONNECTED;

          if ( gapRole_RSSIReadRate )
          {
            // Start the RSSI Reads
            VOID osal_start_timerEx( gapRole_TaskID, RSSI_READ_EVT, gapRole_RSSIReadRate );
          }

          // Store connection information
          gapRole_ConnInterval = pPkt->connInterval;
          gapRole_ConnSlaveLatency = pPkt->connLatency;
          gapRole_ConnTimeout = pPkt->connTimeout;

          // Check whether update parameter request is enabled
          if ( gapRole_ParamUpdateEnable == TRUE )
          {
            // Get the minimum time upon connection establishment before the 
            // peripheral can start a connection update procedure.
            uint16 timeout = GAP_GetParamValue( TGAP_CONN_PAUSE_PERIPHERAL );

            osal_start_timerEx( gapRole_TaskID, START_CONN_UPDATE_EVT, timeout*1000 );
          }

          // Notify the Bond Manager to the connection
          VOID GAPBondMgr_LinkEst( pPkt->devAddrType, pPkt->devAddr, pPkt->connectionHandle, GAP_PROFILE_PERIPHERAL );

          // Set enabler to FALSE; device will become discoverable again when
          // this value gets set to TRUE
          gapRole_AdvEnabled = FALSE;          
        }
        else if ( pPkt->hdr.status == bleGAPConnNotAcceptable )
        {
          // Set enabler to FALSE; device will become discoverable again when
          // this value gets set to TRUE
          gapRole_AdvEnabled = FALSE;

          // Go to WAITING state, and then start advertising
          gapRole_state = GAPROLE_WAITING;
        }
        else
        {
          gapRole_state = GAPROLE_ERROR;
        }
        notify = TRUE;
      }
      break;
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osal_start_timerEx( gapRole_TaskID, START_CONN_UPDATE_EVT, timeout*1000 );
这个事件便是发起连接参数更新，这个timeout是为了让连接更稳定，在建立连接之后得经过一段稳定的时间在更新参数

有网友的做法是在peripheralStateNotificationCB函数中的GAPROLE_CONNECTED里面添加更新参数的函数手动发起更新请求，不知这种做法是否有风险。

GAPRole_SendUpdateParam( uint16 minConnInterval, uint16 maxConnInterval,
                                   uint16 latency, uint16 connTimeout, uint8 handleFailure );
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也可以用下面这个中方式，两者本质都是用gapRole_startConnUpdate( GAPROLE_NO_ACTION );

GAPRole_SetParameter( GAPROLE_PARAM_UPDATE_REQ, sizeof ( uint8 ), TRUE );
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怎么获取实时连接参数？
好办！
如下函数，注册一个回调函数，然后就可以得到connInterval，connSlaveLatency，connTimeout这三项参数，当参数更新成功是进入回调；因此可以在回调函数里面用LCD，打印，发给APP等等各种方式来展示

GAPRole_RegisterAppCBs( gapRolesParamUpdateCB_t *pParamUpdateCB );
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顺便贴一下回调函数的调用：

 case GAP_LINK_PARAM_UPDATE_EVENT:
      {
        gapLinkUpdateEvent_t *pPkt = (gapLinkUpdateEvent_t *)pMsg;

        // Cancel connection param update timeout timer (if active)
        VOID osal_stop_timerEx( gapRole_TaskID, CONN_PARAM_TIMEOUT_EVT );

        if ( pPkt->hdr.status == SUCCESS )
        {
          // Store new connection parameters
          gapRole_ConnInterval = pPkt->connInterval;
          gapRole_ConnSlaveLatency = pPkt->connLatency;
          gapRole_ConnTimeout = pPkt->connTimeout;

          // Make sure there's no pending connection update procedure
          if ( osal_get_timeoutEx( gapRole_TaskID, START_CONN_UPDATE_EVT ) == 0 )
          {
            // Notify the application with the new connection parameters
            if ( pGapRoles_ParamUpdateCB != NULL )
            {
              (*pGapRoles_ParamUpdateCB)( gapRole_ConnInterval, 
                                          gapRole_ConnSlaveLatency, 
                                          gapRole_ConnTimeout );
            }
          }
        }
      }
      break;