FreeModbus Slave 改进的eMbPoll()【worldsing 笔记】

eMbPoll()的作用是FreeMod协议通信过程中不断查询事件对列有无完速数据桢，并进行地址和CRD验证，最后运行和回复主机。

为了减小代码尺寸对eMbPoll进行改进：

原版：

   1:  

   2: eMBErrorCode

   3: eMBPoll( void )

   4: {

   5:     static UCHAR   *ucMBFrame;

   6:     static UCHAR    ucRcvAddress;

   7:     static UCHAR    ucFunctionCode;

   8:     static USHORT   usLength;

   9:     static eMBException eException;

  10:  

  11:     int             i;

  12:     eMBErrorCode    eStatus = MB_ENOERR;

  13:     eMBEventType    eEvent;

  14:  

  15:     /* Check if the protocol stack is ready. */

  16:     if( eMBState != STATE_ENABLED )

  17:     {

  18:         return MB_EILLSTATE;

  19:     }

  20:  

  21:     /* Check if there is a event available. If not return control to caller.

  22:      * Otherwise we will handle the event. */

  23:     if( xMBPortEventGet( &eEvent ) == TRUE )

  24:     {

  25:         switch ( eEvent )

  26:         {

  27:         case EV_READY:

  28:             break;

  29:  

  30:         case EV_FRAME_RECEIVED:

  31:             eStatus = peMBFrameReceiveCur( &ucRcvAddress, &ucMBFrame, &usLength );

  32:             if( eStatus == MB_ENOERR )

  33:             {

  34:                 /* Check if the frame is for us. If not ignore the frame. */

  35:                 if( ( ucRcvAddress == ucMBAddress ) || ( ucRcvAddress == MB_ADDRESS_BROADCAST ) )

  36:                 {

  37:                     ( void )xMBPortEventPost( EV_EXECUTE );

  38:                 }

  39:             }

  40:             break;

  41:  

  42:         case EV_EXECUTE:

  43:             ucFunctionCode = ucMBFrame[MB_PDU_FUNC_OFF];

  44:             eException = MB_EX_ILLEGAL_FUNCTION;

  45:             for( i = 0; i < MB_FUNC_HANDLERS_MAX; i++ )

  46:             {

  47:                 /* No more function handlers registered. Abort. */

  48:                 if( xFuncHandlers[i].ucFunctionCode == 0 )

  49:                 {

  50:                     break;

  51:                 }

  52:                 else if( xFuncHandlers[i].ucFunctionCode == ucFunctionCode )

  53:                 {

  54:                     eException = xFuncHandlers[i].pxHandler( ucMBFrame, &usLength );

  55:                     break;

  56:                 }

  57:             }

  58:  

  59:             /* If the request was not sent to the broadcast address we

  60:              * return a reply. */

  61:             if( ucRcvAddress != MB_ADDRESS_BROADCAST )

  62:             {

  63:                 if( eException != MB_EX_NONE )

  64:                 {

  65:                     /* An exception occured. Build an error frame. */

  66:                     usLength = 0;

  67:                     ucMBFrame[usLength++] = ( UCHAR )( ucFunctionCode | MB_FUNC_ERROR );

  68:                     ucMBFrame[usLength++] = eException;

  69:                 }

  70:                 if( ( eMBCurrentMode == MB_ASCII ) && MB_ASCII_TIMEOUT_WAIT_BEFORE_SEND_MS )

  71:                 {

  72:                     vMBPortTimersDelay( MB_ASCII_TIMEOUT_WAIT_BEFORE_SEND_MS );

  73:                 }                

  74:                 eStatus = peMBFrameSendCur( ucMBAddress, ucMBFrame, usLength );

  75:             }

  76:             break;

  77:  

  78:         case EV_FRAME_SENT:

  79:             break;

  80:         }

  81:     }

  82:     return MB_ENOERR;

  83: }

改进后的eMbPoll():

   1:  

   2: void eMBPoll( void ){

   3:   

   4:   static UCHAR   *ucMBFrame;

   5:   static UCHAR    ucFunctionCode;

   6:   static USHORT   usLength;

   7:   static eMBException eException;

   8:   eMBEventType    eEvent;

   9:   UCHAR i;

  10:   USHORT usCRC16;

  11:   if(xMBPortEventGet( &eEvent) == TRUE ){                             //桢事件判断

  12:     if(eEvent == EV_FRAME_RECEIVED){    

  13:       if(usRcvBufferPos < MB_SER_PDU_SIZE_MIN)                        //最小桢判断

  14:         return;

  15:       if(usMBCRC16((UCHAR *)ucRTUBuf, usRcvBufferPos ) != 0)          //CRC判断

  16:         return;

  17:       if(IS_VALID_ADD){                                               //地址    

  18:         ucMBFrame = (UCHAR *) &ucRTUBuf[MB_SER_PDU_PDU_OFF];    

  19:         usLength = (USHORT)( usRcvBufferPos - MB_SER_PDU_PDU_OFF - MB_SER_PDU_SIZE_CRC);

  20:         ucFunctionCode = ucMBFrame[MB_PDU_FUNC_OFF];

  21:         eException = MB_EX_ILLEGAL_FUNCTION;

  22:         for(i = 0; i < MB_FUNC_HANDLERS_MAX; i++ ){                  //执行功能码

  23:           if( xFuncHandlers[i].ucFunctionCode == 0 ){

  24:             return;

  25:           }

  26:           else if( xFuncHandlers[i].ucFunctionCode == ucFunctionCode ){

  27:             eException = xFuncHandlers[i].pxHandler( ucMBFrame, &usLength );

  28:             break;                               

  29:           }

  30:       }

  31:       if(IS_NOT_BROADCAST){                                        //回复主机

  32:         if( eException != MB_EX_NONE ){                            //错误码         

  33:           usLength = 0;

  34:           ucMBFrame[usLength++] = ( UCHAR )( ucFunctionCode | MB_FUNC_ERROR );

  35:           ucMBFrame[usLength++] = eException;

  36:         } 

  37:         if(eRcvState == STATE_RX_IDLE){                            //发送

  38:           pucSndBufferCur = ( UCHAR * ) ucMBFrame - 1;

  39:           pucSndBufferCur[MB_SER_PDU_ADDR_OFF] = ucMBAddress;

  40:           usSndBufferCount = usLength + 1;      

  41:           usCRC16 = usMBCRC16( ( UCHAR * ) pucSndBufferCur, usSndBufferCount );

  42:           ucRTUBuf[usSndBufferCount++] = ( UCHAR )( usCRC16 & 0xFF );

  43:           ucRTUBuf[usSndBufferCount++] = ( UCHAR )( usCRC16 >> 8 );    

  44:           eSndState = STATE_TX_XMIT;

  45:           vMBPortSerialEnable( FALSE, TRUE );

  46:           }//发送结束

  47:         }//回复结束

  48:       }//地址判断

  49:     }//桢事件判断

  50:   }

  51: }

改进说明：

1、eMbPoll（）调用一次即可运行功能码和回复主机；

2、省去独立的接收函数peMBFrameReceiveCur( &ucRcvAddress, &ucMBFrame, &usLength ); 而直接操作，（其实里面对算出数据桢的启始位置、和长度）；

3、省去发送函数peMBFrameSendCur( ucMBAddress, ucMBFrame, usLength ); 而直接操作；

4、省去返回值，因为调用处没有使用；

5、对功能的遍历i改成unsigned char类型，省去ucRcvAddress和eMBErrorCode    eStatus = MB_ENOERR; 变量，

6、功能兼容原版本。

eMbPoll的经典之处在于功能的运行，——》函数指针，这部分在其它笔记中记录。