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：

eMBErrorCode
eMBPoll( void )
{
    static UCHAR   *ucMBFrame;
    static UCHAR    ucRcvAddress;
    static UCHAR    ucFunctionCode;
    static USHORT   usLength;
    static eMBException eException;

    int             i;
    eMBErrorCode    eStatus = MB_ENOERR;
    eMBEventType    eEvent;

    /* Check if the protocol stack is ready. */
    if( eMBState != STATE_ENABLED )
    {
        return MB_EILLSTATE;
    }

    /* Check if there is a event available. If not return control to caller.
     * Otherwise we will handle the event. */
    if( xMBPortEventGet( &eEvent ) == TRUE )
    {
        switch ( eEvent )
        {
        case EV_READY:
            break;

        case EV_FRAME_RECEIVED:
            eStatus = peMBFrameReceiveCur( &ucRcvAddress, &ucMBFrame, &usLength );
            if( eStatus == MB_ENOERR )
            {
                /* Check if the frame is for us. If not ignore the frame. */
                if( ( ucRcvAddress == ucMBAddress ) || ( ucRcvAddress == MB_ADDRESS_BROADCAST ) )
                {
                    ( void )xMBPortEventPost( EV_EXECUTE );
                }
            }
            break;

        case EV_EXECUTE:
            ucFunctionCode = ucMBFrame[MB_PDU_FUNC_OFF];
            eException = MB_EX_ILLEGAL_FUNCTION;
            for( i = 0; i < MB_FUNC_HANDLERS_MAX; i++ )
            {
                /* No more function handlers registered. Abort. */
                if( xFuncHandlers[i].ucFunctionCode == 0 )
                {
                    break;
                }
                else if( xFuncHandlers[i].ucFunctionCode == ucFunctionCode )
                {
                    eException = xFuncHandlers[i].pxHandler( ucMBFrame, &usLength );
                    break;
                }
            }

            /* If the request was not sent to the broadcast address we
             * return a reply. */
            if( ucRcvAddress != MB_ADDRESS_BROADCAST )
            {
                if( eException != MB_EX_NONE )
                {
                    /* An exception occured. Build an error frame. */
                    usLength = 0;
                    ucMBFrame[usLength++] = ( UCHAR )( ucFunctionCode | MB_FUNC_ERROR );
                    ucMBFrame[usLength++] = eException;
                }
                if( ( eMBCurrentMode == MB_ASCII ) && MB_ASCII_TIMEOUT_WAIT_BEFORE_SEND_MS )
                {
                    vMBPortTimersDelay( MB_ASCII_TIMEOUT_WAIT_BEFORE_SEND_MS );
                }
                eStatus = peMBFrameSendCur( ucMBAddress, ucMBFrame, usLength );
            }
            break;

        case EV_FRAME_SENT:
            break;
        }
    }
    return MB_ENOERR;
}

 

改进后的eMbPoll():

void eMBPoll( void ){

  static UCHAR   *ucMBFrame;
  static UCHAR    ucFunctionCode;
  static USHORT   usLength;
  static eMBException eException;
  eMBEventType    eEvent;
  UCHAR i;
  USHORT usCRC16;
  if(xMBPortEventGet( &eEvent) == TRUE ){                             //桢事件判断
    if(eEvent == EV_FRAME_RECEIVED){
      if(usRcvBufferPos < MB_SER_PDU_SIZE_MIN)                        //最小桢判断
        return;
      if(usMBCRC16((UCHAR *)ucRTUBuf, usRcvBufferPos ) != 0)          //CRC判断
        return;
      if(IS_VALID_ADD){                                               //地址
        ucMBFrame = (UCHAR *) &ucRTUBuf[MB_SER_PDU_PDU_OFF];
        usLength = (USHORT)( usRcvBufferPos - MB_SER_PDU_PDU_OFF - MB_SER_PDU_SIZE_CRC);
        ucFunctionCode = ucMBFrame[MB_PDU_FUNC_OFF];
        eException = MB_EX_ILLEGAL_FUNCTION;
        for(i = 0; i < MB_FUNC_HANDLERS_MAX; i++ ){                  //执行功能码
          if( xFuncHandlers[i].ucFunctionCode == 0 ){
            return;
          }
          else if( xFuncHandlers[i].ucFunctionCode == ucFunctionCode ){
            eException = xFuncHandlers[i].pxHandler( ucMBFrame, &usLength );
            break;
          }
      }
      if(IS_NOT_BROADCAST){                                        //回复主机
        if( eException != MB_EX_NONE ){                            //错误码
          usLength = 0;
          ucMBFrame[usLength++] = ( UCHAR )( ucFunctionCode | MB_FUNC_ERROR );
          ucMBFrame[usLength++] = eException;
        }
        if(eRcvState == STATE_RX_IDLE){                            //发送
          pucSndBufferCur = ( UCHAR * ) ucMBFrame - 1;
          pucSndBufferCur[MB_SER_PDU_ADDR_OFF] = ucMBAddress;
          usSndBufferCount = usLength + 1;
          usCRC16 = usMBCRC16( ( UCHAR * ) pucSndBufferCur, usSndBufferCount );
          ucRTUBuf[usSndBufferCount++] = ( UCHAR )( usCRC16 & 0xFF );
          ucRTUBuf[usSndBufferCount++] = ( UCHAR )( usCRC16 >> 8 );
          eSndState = STATE_TX_XMIT;
          vMBPortSerialEnable( FALSE, TRUE );
          }//发送结束
        }//回复结束
      }//地址判断
    }//桢事件判断
  }
}

 

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。