/*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (C) 2006 Christian Walter <wolti@sil.at>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  *
  * File: $Id: mbtcp.c,v 1.2 2006/06/26 19:27:04 wolti Exp $
  */

/* ----------------------- System includes ----------------------------------*/
#include "stdlib.h"
#include "string.h"

/* ----------------------- Platform includes --------------------------------*/
#include "port.h"

/* ----------------------- Modbus includes ----------------------------------*/
#include "mb.h"
#include "mbconfig.h"
#include "mbtcp.h"
#include "mbframe.h"
#include "mbport.h"

#if MB_TCP_ENABLED > 0

/* ----------------------- Defines ------------------------------------------*/

/* ----------------------- MBAP Header --------------------------------------*/
/*
 *
 * <------------------------ MODBUS TCP/IP ADU(1) ------------------------->
 *              <----------- MODBUS PDU (1') ---------------->
 *  +-----------+---------------+------------------------------------------+
 *  | TID | PID | Length | UID  |Code | Data                               |
 *  +-----------+---------------+------------------------------------------+
 *  |     |     |        |      |                                           
 * (2)   (3)   (4)      (5)    (6)                                          
 *
 * (2)  ... MB_TCP_TID          = 0 (Transaction Identifier - 2 Byte) 
 * (3)  ... MB_TCP_PID          = 2 (Protocol Identifier - 2 Byte)
 * (4)  ... MB_TCP_LEN          = 4 (Number of bytes - 2 Byte)
 * (5)  ... MB_TCP_UID          = 6 (Unit Identifier - 1 Byte)
 * (6)  ... MB_TCP_FUNC         = 7 (Modbus Function Code)
 *
 * (1)  ... Modbus TCP/IP Application Data Unit
 * (1') ... Modbus Protocol Data Unit
 */

#define MB_TCP_TID          0
#define MB_TCP_PID          2
#define MB_TCP_LEN          4
#define MB_TCP_UID          6
#define MB_TCP_FUNC         7

#define MB_TCP_PROTOCOL_ID  0   /* 0 = Modbus Protocol */


/* ----------------------- Start implementation -----------------------------*/
eMBErrorCode
eMBTCPDoInit( USHORT ucTCPPort )
{
    eMBErrorCode    eStatus = MB_ENOERR;

    if( xMBTCPPortInit( ucTCPPort ) == FALSE )
    {
        eStatus = MB_EPORTERR;
    }
    return eStatus;
}

void
eMBTCPStart( void )
{
}

void
eMBTCPStop( void )
{
    /* Make sure that no more clients are connected. */
    vMBTCPPortDisable( );
}

eMBErrorCode
eMBTCPReceive( UCHAR * pucRcvAddress, UCHAR ** ppucFrame, USHORT * pusLength )
{
    eMBErrorCode    eStatus = MB_EIO;
    UCHAR          *pucMBTCPFrame;
    USHORT          usLength;
    USHORT          usPID;

    if( xMBTCPPortGetRequest( &pucMBTCPFrame, &usLength ) != FALSE )
    {
        usPID = pucMBTCPFrame[MB_TCP_PID] << 8U;
        usPID |= pucMBTCPFrame[MB_TCP_PID + 1];

        if( usPID == MB_TCP_PROTOCOL_ID )
        {
            *ppucFrame = &pucMBTCPFrame[MB_TCP_FUNC];
            *pusLength = usLength - MB_TCP_FUNC;
            eStatus = MB_ENOERR;

            /* Modbus TCP does not use any addresses. Fake the source address such
             * that the processing part deals with this frame.
             */
            *pucRcvAddress = MB_TCP_PSEUDO_ADDRESS;
        }
    }
    else
    {
        eStatus = MB_EIO;
    }
    return eStatus;
}

eMBErrorCode
eMBTCPSend( UCHAR _unused, const UCHAR * pucFrame, USHORT usLength )
{
    eMBErrorCode    eStatus = MB_ENOERR;
    UCHAR          *pucMBTCPFrame = ( UCHAR * ) pucFrame - MB_TCP_FUNC;
    USHORT          usTCPLength = usLength + MB_TCP_FUNC;

    /* The MBAP header is already initialized because the caller calls this
     * function with the buffer returned by the previous call. Therefore we 
     * only have to update the length in the header. Note that the length 
     * header includes the size of the Modbus PDU and the UID Byte. Therefore 
     * the length is usLength plus one.
     */
    pucMBTCPFrame[MB_TCP_LEN] = ( usLength + 1 ) >> 8U;
    pucMBTCPFrame[MB_TCP_LEN + 1] = ( usLength + 1 ) & 0xFF;
    if( xMBTCPPortSendResponse( pucMBTCPFrame, usTCPLength ) == FALSE )
    {
        eStatus = MB_EIO;
    }
    return eStatus;
}

#endif