mbfuncdisc.c

/* 
 * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
 * Copyright (c) 2006-2018 Christian Walter <cwalter@embedded-solutions.at>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

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

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

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

/* ----------------------- Defines ------------------------------------------*/
#define MB_PDU_FUNC_READ_ADDR_OFF           ( MB_PDU_DATA_OFF )
#define MB_PDU_FUNC_READ_DISCCNT_OFF        ( MB_PDU_DATA_OFF + 2 )
#define MB_PDU_FUNC_READ_SIZE               ( 4 )
#define MB_PDU_FUNC_READ_DISCCNT_MAX        ( 0x07D0 )

/* ----------------------- Static functions ---------------------------------*/
eMBException    prveMBError2Exception( eMBErrorCode eErrorCode );

/* ----------------------- Start implementation -----------------------------*/

#if MB_FUNC_READ_COILS_ENABLED > 0

eMBException
eMBFuncReadDiscreteInputs( UCHAR * pucFrame, USHORT * usLen )
{
    USHORT          usRegAddress;
    USHORT          usDiscreteCnt;
    UCHAR           ucNBytes;
    UCHAR          *pucFrameCur;

    eMBException    eStatus = MB_EX_NONE;
    eMBErrorCode    eRegStatus;

    if( *usLen == ( MB_PDU_FUNC_READ_SIZE + MB_PDU_SIZE_MIN ) )
    {
        usRegAddress = ( USHORT )( pucFrame[MB_PDU_FUNC_READ_ADDR_OFF] << 8 );
        usRegAddress |= ( USHORT )( pucFrame[MB_PDU_FUNC_READ_ADDR_OFF + 1] );
        usRegAddress++;

        usDiscreteCnt = ( USHORT )( pucFrame[MB_PDU_FUNC_READ_DISCCNT_OFF] << 8 );
        usDiscreteCnt |= ( USHORT )( pucFrame[MB_PDU_FUNC_READ_DISCCNT_OFF + 1] );

        /* Check if the number of registers to read is valid. If not
         * return Modbus illegal data value exception. 
         */
        if( ( usDiscreteCnt >= 1 ) &&
            ( usDiscreteCnt < MB_PDU_FUNC_READ_DISCCNT_MAX ) )
        {
            /* Set the current PDU data pointer to the beginning. */
            pucFrameCur = &pucFrame[MB_PDU_FUNC_OFF];
            *usLen = MB_PDU_FUNC_OFF;

            /* First byte contains the function code. */
            *pucFrameCur++ = MB_FUNC_READ_DISCRETE_INPUTS;
            *usLen += 1;

            /* Test if the quantity of coils is a multiple of 8. If not last
             * byte is only partially field with unused coils set to zero. */
            if( ( usDiscreteCnt & 0x0007 ) != 0 )
            {
                ucNBytes = ( UCHAR ) ( usDiscreteCnt / 8 + 1 );
            }
            else
            {
                ucNBytes = ( UCHAR ) ( usDiscreteCnt / 8 );
            }
            *pucFrameCur++ = ucNBytes;
            *usLen += 1;

            eRegStatus =
                eMBRegDiscreteCB( pucFrameCur, usRegAddress, usDiscreteCnt );

            /* If an error occured convert it into a Modbus exception. */
            if( eRegStatus != MB_ENOERR )
            {
                eStatus = prveMBError2Exception( eRegStatus );
            }
            else
            {
                /* The response contains the function code, the starting address
                 * and the quantity of registers. We reuse the old values in the 
                 * buffer because they are still valid. */
                *usLen += ucNBytes;;
            }
        }
        else
        {
            eStatus = MB_EX_ILLEGAL_DATA_VALUE;
        }
    }
    else
    {
        /* Can't be a valid read coil register request because the length
         * is incorrect. */
        eStatus = MB_EX_ILLEGAL_DATA_VALUE;
    }
    return eStatus;
}

#endif