BLE 自动断开连接

用BLE协议栈里两个程序，simpleBLECentral，SimpleBLEPeripheral。Central进行扫描后再成功连接了一个设备。为什么过了一段时间后又自动断开了，大概是20秒，中间也无法发送数据，获取HAND值，求解答，谢谢。

调试能进入这段函数：case GAP_LINK_ESTABLISHED_EVENT:
      {
        if ( pEvent->gap.hdr.status == SUCCESS )
        {          
          simpleBLEState = BLE_STATE_CONNECTED;
          simpleBLEConnHandle = pEvent->linkCmpl.connectionHandle;
     
          simpleBLEProcedureInProgress = TRUE;    

          // If service discovery not performed initiate service discovery
       if ( simpleBLECharHdl == 0 )
          {
           osal_start_timerEx( simpleBLETaskId, START_DISCOVERY_EVT, DEFAULT_SVC_DISCOVERY_DELAY );
      }
          
     
          
      
          LCD_WRITE_STRING( "Connected", HAL_LCD_LINE_1 );
          LCD_WRITE_STRING( bdAddr2Str( pEvent->linkCmpl.devAddr ), HAL_LCD_LINE_2 );  
          
          
          HalUARTWrite(0,"---Connected---",15);
           HalUARTWrite(0,bdAddr2Str( pEvent->linkCmpl.devAddr ),14);
         
          
        }