libmodbus/modbus/modbus.c

/*
 * Copyright © 2001-2008 Stéphane Raimbault <stephane.raimbault@gmail.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 Public License for more details.
 *
 * You should have received a copy of the GNU Lesser Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
   The library is designed to send and receive data from a device that
   communicate via the Modbus protocol.

   The function names used are inspired by the Modicon Modbus Protocol
   Reference Guide which can be obtained from Schneider at
   www.schneiderautomation.com.
    
   Documentation:
   http://www.easysw.com/~mike/serial/serial.html
   http://copyleft.free.fr/wordpress/index.php/libmodbus/
*/

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <termios.h>
#include <sys/time.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>
#include <fcntl.h>

/* TCP */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>

#include "modbus.h"

#define UNKNOWN_ERROR_MSG "Not defined in modbus specification"

static const uint8_t NB_TAB_ERROR_MSG = 12;
static const char *TAB_ERROR_MSG[] = {
        /* 0x00 */ UNKNOWN_ERROR_MSG,
        /* 0x01 */ "Illegal function code",
        /* 0x02 */ "Illegal data address",
        /* 0x03 */ "Illegal data value",
        /* 0x04 */ "Slave device or server failure",
        /* 0x05 */ "Acknowledge",
        /* 0x06 */ "Slave device or server busy",
        /* 0x07 */ "Negative acknowledge",
        /* 0x08 */ "Memory parity error",
        /* 0x09 */ UNKNOWN_ERROR_MSG,
        /* 0x0A */ "Gateway path unavailable",
        /* 0x0B */ "Target device failed to respond"
};

/* Table of CRC values for high-order byte */
static uint8_t table_crc_hi[] = {
        0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 
        0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 
        0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 
        0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 
        0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 
        0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 
        0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 
        0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 
        0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 
        0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 
        0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 
        0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 
        0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 
        0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 
        0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 
        0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 
        0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 
        0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 
        0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 
        0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 
        0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 
        0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 
        0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 
        0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 
        0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 
        0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
};

/* Table of CRC values for low-order byte */
static uint8_t table_crc_lo[] = {
        0x00, 0xC0, 0xC1, 0x01, 0xC3, 0x03, 0x02, 0xC2, 0xC6, 0x06, 
        0x07, 0xC7, 0x05, 0xC5, 0xC4, 0x04, 0xCC, 0x0C, 0x0D, 0xCD, 
        0x0F, 0xCF, 0xCE, 0x0E, 0x0A, 0xCA, 0xCB, 0x0B, 0xC9, 0x09, 
        0x08, 0xC8, 0xD8, 0x18, 0x19, 0xD9, 0x1B, 0xDB, 0xDA, 0x1A, 
        0x1E, 0xDE, 0xDF, 0x1F, 0xDD, 0x1D, 0x1C, 0xDC, 0x14, 0xD4, 
        0xD5, 0x15, 0xD7, 0x17, 0x16, 0xD6, 0xD2, 0x12, 0x13, 0xD3, 
        0x11, 0xD1, 0xD0, 0x10, 0xF0, 0x30, 0x31, 0xF1, 0x33, 0xF3, 
        0xF2, 0x32, 0x36, 0xF6, 0xF7, 0x37, 0xF5, 0x35, 0x34, 0xF4, 
        0x3C, 0xFC, 0xFD, 0x3D, 0xFF, 0x3F, 0x3E, 0xFE, 0xFA, 0x3A, 
        0x3B, 0xFB, 0x39, 0xF9, 0xF8, 0x38, 0x28, 0xE8, 0xE9, 0x29, 
        0xEB, 0x2B, 0x2A, 0xEA, 0xEE, 0x2E, 0x2F, 0xEF, 0x2D, 0xED, 
        0xEC, 0x2C, 0xE4, 0x24, 0x25, 0xE5, 0x27, 0xE7, 0xE6, 0x26, 
        0x22, 0xE2, 0xE3, 0x23, 0xE1, 0x21, 0x20, 0xE0, 0xA0, 0x60, 
        0x61, 0xA1, 0x63, 0xA3, 0xA2, 0x62, 0x66, 0xA6, 0xA7, 0x67, 
        0xA5, 0x65, 0x64, 0xA4, 0x6C, 0xAC, 0xAD, 0x6D, 0xAF, 0x6F, 
        0x6E, 0xAE, 0xAA, 0x6A, 0x6B, 0xAB, 0x69, 0xA9, 0xA8, 0x68, 
        0x78, 0xB8, 0xB9, 0x79, 0xBB, 0x7B, 0x7A, 0xBA, 0xBE, 0x7E, 
        0x7F, 0xBF, 0x7D, 0xBD, 0xBC, 0x7C, 0xB4, 0x74, 0x75, 0xB5, 
        0x77, 0xB7, 0xB6, 0x76, 0x72, 0xB2, 0xB3, 0x73, 0xB1, 0x71, 
        0x70, 0xB0, 0x50, 0x90, 0x91, 0x51, 0x93, 0x53, 0x52, 0x92, 
        0x96, 0x56, 0x57, 0x97, 0x55, 0x95, 0x94, 0x54, 0x9C, 0x5C, 
        0x5D, 0x9D, 0x5F, 0x9F, 0x9E, 0x5E, 0x5A, 0x9A, 0x9B, 0x5B, 
        0x99, 0x59, 0x58, 0x98, 0x88, 0x48, 0x49, 0x89, 0x4B, 0x8B, 
        0x8A, 0x4A, 0x4E, 0x8E, 0x8F, 0x4F, 0x8D, 0x4D, 0x4C, 0x8C, 
        0x44, 0x84, 0x85, 0x45, 0x87, 0x47, 0x46, 0x86, 0x82, 0x42, 
        0x43, 0x83, 0x41, 0x81, 0x80, 0x40
};

/* Local declaration */
static int read_reg_response(modbus_param_t *mb_param, 
                             uint16_t *data_dest, uint8_t *query);

/* Treats errors and flush or close connection if necessary */
static void error_treat(modbus_param_t *mb_param, int code, const char *string)
{
        printf("\nERROR %s (%d)\n", string, code);

        if (mb_param->error_handling == FLUSH_OR_RECONNECT_ON_ERROR) {
                switch (code) {
                case ILLEGAL_DATA_VALUE:
                case ILLEGAL_DATA_ADDRESS:
                case ILLEGAL_FUNCTION:
                        break;
                default:
                        if (mb_param->type_com == RTU) {
                                tcflush(mb_param->fd, TCIOFLUSH);
                        } else {
                                modbus_close(mb_param);
                                modbus_connect(mb_param);
                        }
                }
        }
}

/* Computes the length of the expected response */
static unsigned int compute_response_length(modbus_param_t *mb_param, 
                                            uint8_t *query)
{
        int resp_length;
        int offset;

        offset = mb_param->header_length;

        switch (query[offset + 1]) {
        case FC_READ_COIL_STATUS:
        case FC_READ_INPUT_STATUS: {
                /* Header + nb values (code from force_multiple_coils) */
                int nb_points = (query[offset + 4] << 8) | query[offset + 5];
                resp_length = 3 + (nb_points / 8) + ((nb_points % 8) ? 1 : 0);
        }
                break;
        case FC_READ_HOLDING_REGISTERS:
        case FC_READ_INPUT_REGISTERS:
                /* Header + 2 * nb values */
                resp_length = 3 + 2 * (query[offset + 4] << 8 | query[offset + 5]);
                break;
        case FC_READ_EXCEPTION_STATUS:
                resp_length = 4;
                break;
        default:
                resp_length = 6;
        }

        resp_length += offset + mb_param->checksum_length;

        return resp_length;
}

/* Builds a RTU query header */
static int build_query_basis_rtu(int slave, int function,
                                 int start_addr, int count,
                                 uint8_t *query)
{
        query[0] = slave;
        query[1] = function;
        query[2] = start_addr >> 8;
        query[3] = start_addr & 0x00ff;
        query[4] = count >> 8;
        query[5] = count & 0x00ff;

        return PRESET_QUERY_LENGTH_RTU;
}

/* Builds a TCP query header */
static int build_query_basis_tcp(int slave, int function,
                                 int start_addr, int count,
                                 uint8_t *query)
{
        static uint16_t t_id = 0;

        /* Transaction ID */
        if (t_id < UINT16_MAX)
                t_id++;
        else
                t_id = 0;
        query[0] = t_id >> 8;
        query[1] = t_id & 0x00ff;

        /* Protocol Modbus */
        query[2] = 0;
        query[3] = 0;

        /* Length to fix later with set_query_length_tcp (4 and 5) */

        query[6] = slave;
        query[7] = function;
        query[8] = start_addr >> 8;
        query[9] = start_addr & 0x00ff;
        query[10] = count >> 8;
        query[11] = count & 0x00ff;

        return PRESET_QUERY_LENGTH_TCP;
}

static int build_query_basis(modbus_param_t *mb_param, int slave, 
                             int function, int start_addr,
                             int count, uint8_t *query)
{
        if (mb_param->type_com == RTU)
                return build_query_basis_rtu(slave, function, start_addr,
                                             count, query);
        else
                return build_query_basis_tcp(slave, function, start_addr,
                                             count, query);
}

/* Builds a RTU response header */
static int build_response_basis_rtu(int slave, int function, uint8_t *response)
{
        response[0] = slave;
        response[1] = function;

        return PRESET_RESPONSE_LENGTH_RTU;
}

/* Builds a TCP response header */
static int build_response_basis_tcp(int slave, int function, uint8_t *response)
{
        static uint16_t t_id = 0;

        /* Transaction ID */
        if (t_id < USHRT_MAX)
                t_id++;
        else
                t_id = 0;
        response[0] = t_id >> 8;
        response[1] = t_id & 0x00ff;

        /* Protocol Modbus */
        response[2] = 0;
        response[3] = 0;

        /* Length to fix later with set_message_length_tcp (4 and 5) */

        response[6] = slave;
        response[7] = function;

        return PRESET_RESPONSE_LENGTH_TCP;
}

static int build_response_basis(modbus_param_t *mb_param, int slave, 
                                int function, uint8_t *response)
{
        if (mb_param->type_com == RTU)
                return build_response_basis_rtu(slave, function, response);
        else
                return build_response_basis_tcp(slave, function, response);
}

/* Sets the length of TCP message in the message (query and response) */
void set_message_length_tcp(uint8_t *msg, int msg_length)
{
        /* Substract the header length to the message length */
        int mbap_length = msg_length - 6;

        msg[4] = mbap_length >> 8;
        msg[5] = mbap_length & 0x00FF;
}

/* Fast CRC */
static uint16_t crc16(uint8_t *buffer, uint16_t buffer_length)
{
        uint8_t crc_hi = 0xFF; /* high CRC byte initialized */
        uint8_t crc_lo = 0xFF; /* low CRC byte initialized */
        unsigned int i; /* will index into CRC lookup */

        /* pass through message buffer */
        while (buffer_length--) {
                i = crc_hi ^ *buffer++; /* calculate the CRC  */
                crc_hi = crc_lo ^ table_crc_hi[i];
                crc_lo = table_crc_lo[i];
        }

        return (crc_hi << 8 | crc_lo);
}

/* If CRC is correct returns 0 else returns INVALID_CRC */
int check_crc16(modbus_param_t *mb_param,
                uint8_t *msg,
                const int msg_length)
{
        int ret;
        
        if (mb_param->type_com == RTU) {
                uint16_t crc_calc;
                uint16_t crc_received;
                
                crc_calc = crc16(msg, msg_length - 2);
                crc_received = (msg[msg_length - 2] << 8) | msg[msg_length - 1];
                
                /* Check CRC of msg */
                if (crc_calc == crc_received) {
                        ret = 0;
                } else {
                        char s_error[64];
                        sprintf(s_error, "invalid crc received %0X - crc_calc %0X", 
                                crc_received, crc_calc);
                        ret = INVALID_CRC;
                        error_treat(mb_param, ret, s_error);
                }
        } else {
                /* In TCP, the modbus CRC is not present (see HDLC level) */
                ret = 0;
        }

        return ret;
}

/* Sends a query/response over a serial or a TCP communication */
static int modbus_send(modbus_param_t *mb_param, uint8_t *query,
                       int query_length)
{
        int ret;
        uint16_t s_crc;
        int i;
        
        if (mb_param->type_com == RTU) {
                s_crc = crc16(query, query_length);
                query[query_length++] = s_crc >> 8;
                query[query_length++] = s_crc & 0x00FF;
        } else {
                set_message_length_tcp(query, query_length);
        }

        if (mb_param->debug) {
                for (i = 0; i < query_length; i++)
                        printf("[%.2X]", query[i]);
                printf("\n");
        }
        
        if (mb_param->type_com == RTU)
                ret = write(mb_param->fd, query, query_length);
        else
                ret = send(mb_param->fd, query, query_length, 0);

        /* Return the number of bytes written (0 to n)
           or PORT_SOCKET_FAILURE on error */
        if ((ret == -1) || (ret != query_length)) {
                ret = PORT_SOCKET_FAILURE;
                error_treat(mb_param, ret, "Write port/socket failure");
        }
        
        return ret;
}

/* Computes the length of the header following the function code */
static uint8_t compute_query_length_header(int function)
{
        int length;
        
        if (function <= FC_FORCE_SINGLE_COIL ||
            function == FC_PRESET_SINGLE_REGISTER)
                /* Read and single write */
                length = 4;
        else if (function == FC_FORCE_MULTIPLE_COILS ||
                 function == FC_PRESET_MULTIPLE_REGISTERS)
                /* Multiple write */
                length = 5;
        else
                length = 0;
        
        return length;
}

/* Computes the length of the data to write in the query */
static int compute_query_length_data(modbus_param_t *mb_param, uint8_t *msg)
{
        int function = msg[mb_param->header_length + 1];
        int length;
        
        if (function == FC_FORCE_MULTIPLE_COILS ||
            function == FC_PRESET_MULTIPLE_REGISTERS)
                length = msg[mb_param->header_length + 6];
        else
                length = 0;

        length += mb_param->checksum_length;

        return length;
}

#define WAIT_DATA()                                                                \
{                                                                                  \
    while ((select_ret = select(mb_param->fd+1, &rfds, NULL, NULL, &tv)) == -1) {  \
            if (errno == EINTR) {                                                  \
                    printf("A non blocked signal was caught\n");                   \
                    /* Necessary after an error */                                 \
                    FD_ZERO(&rfds);                                                \
                    FD_SET(mb_param->fd, &rfds);                                   \
            } else {                                                               \
                    error_treat(mb_param, SELECT_FAILURE, "Select failure");       \
                    return SELECT_FAILURE;                                         \
            }                                                                      \
    }                                                                              \
                                                                                   \
    if (select_ret == 0) {                                                         \
            /* Call to error_treat is done later to manage exceptions */           \
            return COMM_TIME_OUT;                                                  \
    }                                                                              \
}

/* Monitors for the reply from the modbus slave or to receive query
   from a modbus master.
   This function blocks for timeout seconds if there is no reply.

   msg_length_computed must be set to MSG_LENGTH_COMPUTED if undefined

   Returns:
   - 0: OK, <0: error
   - msg_length: number of characters received. */
int receive_msg(modbus_param_t *mb_param,
                int msg_length_computed,
                uint8_t *msg, int *msg_length)
{
        int select_ret;
        int read_ret;
        fd_set rfds;
        struct timeval tv;
        int length_to_read;
        uint8_t *p_msg;
        enum { FUNCTION, BYTE, COMPLETE };
        int state;

        if (mb_param->debug) {
                if (msg_length_computed == MSG_LENGTH_UNDEFINED)
                        printf("Waiting for a message...\n");
                else
                        printf("Waiting for a message (%d bytes)...\n", msg_length_computed);
        }

        /* Add a file descriptor to the set */
        FD_ZERO(&rfds);
        FD_SET(mb_param->fd, &rfds);

        if (msg_length_computed == MSG_LENGTH_UNDEFINED) {
                /* Wait for a message */
                tv.tv_sec = 60;
                tv.tv_usec = 0;

                /* The message length is undefined (query receiving) so
                 * we need to analyse the message step by step.
                 * At the first step, we want to reach the function
                 * code because all packets have this information. */
                msg_length_computed = mb_param->header_length + 2;
                state = FUNCTION;
        } else {
                tv.tv_sec = 0;
                tv.tv_usec = TIME_OUT_BEGIN_OF_TRAME;
                state = COMPLETE;
        }
                
        length_to_read = msg_length_computed;

        select_ret = 0;
        WAIT_DATA();

        /* Read the msg */
        (*msg_length) = 0;
        p_msg = msg;

        while (select_ret) {
                if (mb_param->type_com == RTU)
                        read_ret = read(mb_param->fd, p_msg, length_to_read);
                else
                        read_ret = recv(mb_param->fd, p_msg, length_to_read, 0);

                if (read_ret == -1) {
                        error_treat(mb_param, PORT_SOCKET_FAILURE, "Read port/socket failure");
                        return PORT_SOCKET_FAILURE;
                } else if (read_ret == 0) {
                        printf("Connection closed\n");
                        return CONNECTION_CLOSED;
                }
                        
                /* Sums bytes received */ 
                (*msg_length) += read_ret;
                if ((*msg_length) > MAX_MESSAGE_LENGTH) {
                        error_treat(mb_param, TOO_MANY_DATAS, "Too many datas");
                        return TOO_MANY_DATAS;
                }

                /* Display the hex code of each character received */
                if (mb_param->debug) {
                        int i;
                        for (i=0; i < read_ret; i++)
                                printf("<%.2X>", p_msg[i]);
                }

                if ((*msg_length) < msg_length_computed) {
                        /* Message incomplete */
                        length_to_read = msg_length_computed - (*msg_length);
                } else {
                        switch (state) {
                        case FUNCTION:
                                /* Function code position */
                                length_to_read = compute_query_length_header(msg[mb_param->header_length + 1]);
                                msg_length_computed += length_to_read;
                                state = BYTE;
                                break;
                        case BYTE:
                                length_to_read = compute_query_length_data(mb_param, msg);
                                msg_length_computed += length_to_read;
                                state = COMPLETE;
                                break;
                        case COMPLETE:
                                length_to_read = 0;
                                break;
                        }
                }

                /* Moves the pointer to receive other datas */
                p_msg = &(p_msg[read_ret]);

                if (length_to_read > 0) {
                        /* If no character at the buffer wait
                           TIME_OUT_END_OF_TRAME before to generate an error. */
                        tv.tv_sec = 0;
                        tv.tv_usec = TIME_OUT_END_OF_TRAME;
                        
                        WAIT_DATA();
                } else {
                        /* All chars are received */
                        select_ret = FALSE;
                }
        }
        
        if (mb_param->debug)
                printf("\n");

        /* OK */
        return 0;
}


/* Checks whether the right response is returned with good checksum.

   Returns:
   - the numbers of values (bits or word) if success
   - less than 0 for exception errors

   Note: all functions used to send or receive data with modbus return
   these values. */
static int modbus_check_response(modbus_param_t *mb_param, 
                                 uint8_t *query,
                                 uint8_t *response)
{
        int response_length;
        int response_length_computed;     
        int offset = mb_param->header_length;
        int ret;

        response_length_computed = compute_response_length(mb_param, query);
        ret = receive_msg(mb_param, response_length_computed, response, &response_length);
        if (ret == 0) {
                /* Check message */
                ret = check_crc16(mb_param, response, response_length);
                if (ret != 0)
                        return ret;

                /* Good response */
                switch (response[offset + 1]) {
                case FC_READ_COIL_STATUS:
                case FC_READ_INPUT_STATUS:
                        /* Read functions 1 value = 1 byte */
                        response_length = response[offset + 2];
                        break;
                case FC_READ_HOLDING_REGISTERS:
                case FC_READ_INPUT_REGISTERS:
                        /* Read functions 1 value = 2 bytes */
                        response_length = response[offset + 2] / 2;
                        break;
                case FC_FORCE_MULTIPLE_COILS:
                case FC_PRESET_MULTIPLE_REGISTERS:
                        /* N Write functions */
                        response_length = response[offset + 4] << 8 |
                                response[offset + 5];
                        break;
                case FC_REPORT_SLAVE_ID:
                        /* Report slave ID (bytes received) */
                        break;
                default:
                        /* 1 Write functions & others */
                        response_length = 1;
                }

        } else if (ret == COMM_TIME_OUT &&
                   response_length == offset + 3 + mb_param->checksum_length) {
                /* Optimisation allowed because exception response is
                   the smallest trame in modbus protocol (3) so always
                   raise an timeout error */
                /* CRC */
                ret = check_crc16(mb_param, response, response_length);
                if (ret != 0)
                        return ret;

                /* Check for exception response.
                   0x80 + function is stored in the exception
                   response. */
                if (0x80 + query[offset + 1] == response[offset + 1]) {

                        int exception_code = response[offset + 2];
                        // FIXME check test
                        if (exception_code < NB_TAB_ERROR_MSG) {
                                error_treat(mb_param, -exception_code,
                                            TAB_ERROR_MSG[response[offset + 2]]);
                                /* Modbus error code is negative */
                                return -exception_code;
                        } else {
                                /* The chances are low to hit this
                                   case but can avoid a vicious
                                   segfault */
                                char s_error[64];
                                sprintf(s_error, "Invalid exception code %d", response[offset + 2]);
                                error_treat(mb_param, INVALID_EXCEPTION_CODE, s_error);
                                free(s_error);
                                return INVALID_EXCEPTION_CODE;
                        }
                }
        } else if (ret == COMM_TIME_OUT) {
                error_treat(mb_param, ret, "Communication time out");
                return ret;
        } else {
                return ret;
        }

        return response_length;
}

static int response_io_status(int address, int count,
                              uint8_t *tab_io_status,
                              uint8_t *response, int offset)
{
        int shift = 0;
        int byte = 0;
        int i;

        for (i = address; i < address+count; i++) {
                byte |= tab_io_status[i] << shift;
                if (shift == 7) {
                        /* Byte is full */
                        response[offset++] = byte;
                        byte = shift = 0;
                } else {
                        shift++;
                }
        }

        if (shift != 0)
                response[offset++] = byte;

        return offset;
}

/* Build the exception response */
static int response_exception(modbus_param_t *mb_param, int slave,
                              int function, int exception_code,
                              uint8_t *response)
{
        int response_length;

        response_length = build_response_basis(mb_param, slave,
                                               function + 0x80, response);
        /* Positive exception code */
        response[response_length++] = -exception_code;

        return response_length;
}

/* Manages the received query.
   Analyses the query and constructs a response.
   If an error occurs, this function construct the response
   accordingly.
*/
void manage_query(modbus_param_t *mb_param, uint8_t *query,
                  int query_length, modbus_mapping_t *mb_mapping)
{                   
        int offset = mb_param->header_length;
        int slave = query[offset];
        int function = query[offset+1];
        uint16_t address = (query[offset+2] << 8) + query[offset+3];
        uint8_t response[MAX_MESSAGE_LENGTH];
        int resp_length = 0;

        switch (function) {
        case FC_READ_COIL_STATUS: {
                int count = (query[offset+4] << 8) + query[offset+5];
                
                if ((address + count) > mb_mapping->nb_coil_status) {
                        printf("Illegal data address %0X in read_coil_status\n",
                               address + count); 
                        resp_length = response_exception(mb_param, slave, function,
                                                         ILLEGAL_DATA_ADDRESS, response);  
                } else {
                        resp_length = build_response_basis(mb_param, slave, function, response);
                        response[resp_length++] = (count / 8) + ((count % 8) ? 1 : 0);
                        resp_length = response_io_status(address, count,
                                                         mb_mapping->tab_coil_status,
                                                         response, resp_length);
                }
        }
                break;
        case FC_READ_INPUT_STATUS: {
                /* Similar to coil status */
                int count = (query[offset+4] << 8) + query[offset+5];

                if ((address + count) > mb_mapping->nb_input_status) {
                        printf("Illegal data address %0X in read_input_status\n",
                               address + count); 
                        resp_length = response_exception(mb_param, slave, function,
                                                         ILLEGAL_DATA_ADDRESS, response);
                } else {
                        resp_length = build_response_basis(mb_param, slave, function, response);
                        response[resp_length++] = (count / 8) + ((count % 8) ? 1 : 0);
                        resp_length = response_io_status(address, count,
                                                         mb_mapping->tab_input_status,
                                                         response, resp_length);
                }
        }
                break;
        case FC_READ_HOLDING_REGISTERS: {
                int count = (query[offset+4] << 8) + query[offset+5];
                        
                if ((address + count) > mb_mapping->nb_holding_registers) {
                        printf("Illegal data address %0X in read_holding_registers\n",
                               address + count); 
                        resp_length = response_exception(mb_param, slave, function,
                                                         ILLEGAL_DATA_ADDRESS, response);
                } else {
                        int i;
                        
                        resp_length = build_response_basis(mb_param, slave, function, response);
                        response[resp_length++] = count << 1;
                        for (i = address; i < address + count; i++) {
                                response[resp_length++] = mb_mapping->tab_holding_registers[i] >> 8;
                                response[resp_length++] = mb_mapping->tab_holding_registers[i] & 0xFF;
                        }
                }
        }
                break;
        case FC_READ_INPUT_REGISTERS: {
                /* Similar to holding registers */
                int count = (query[offset+4] << 8) + query[offset+5];

                if ((address + count) > mb_mapping->nb_input_registers) {
                        printf("Illegal data address %0X in read_input_registers\n",
                               address + count);
                        resp_length = response_exception(mb_param, slave, function,
                                                         ILLEGAL_DATA_ADDRESS, response);
                } else {
                        int i;

                        resp_length = build_response_basis(mb_param, slave, function, response);
                        response[resp_length++] = count << 1;
                        for (i = address; i < address + count; i++) {
                                response[resp_length++] = mb_mapping->tab_input_registers[i] >> 8;
                                response[resp_length++] = mb_mapping->tab_input_registers[i] & 0xFF;
                        }
                }
        }
                break;
        case FC_FORCE_SINGLE_COIL:
                if (address >= mb_mapping->nb_coil_status) {
                        printf("Illegal data address %0X in force_singe_coil\n", address); 
                        resp_length = response_exception(mb_param, slave, function,
                                                         ILLEGAL_DATA_ADDRESS, response);  
                } else {
                        int data = (query[offset+4] << 8) + query[offset+5];
                        
                        if (data == 0xFF00 || data == 0x0) {
                                mb_mapping->tab_coil_status[address] = (data) ? ON : OFF;

                                /* In RTU mode, the CRC is computed
                                   and added to the query by modbus_send */
                                memcpy(response, query, query_length - mb_param->checksum_length);
                                resp_length = query_length;
                        } else {
                                printf("Illegal data value %0X in force_single_coil request at address %0X\n",
                                       data, address);
                                resp_length = response_exception(mb_param, slave, function,
                                                                 ILLEGAL_DATA_VALUE, response);
                        }
                }
                break;          
        case FC_PRESET_SINGLE_REGISTER:
                if (address >= mb_mapping->nb_holding_registers) {
                        printf("Illegal data address %0X in preset_holding_register\n", address); 
                        resp_length = response_exception(mb_param, slave, function,
                                                         ILLEGAL_DATA_ADDRESS, response);  
                } else {
                        int data = (query[offset+4] << 8) + query[offset+5];
                        
                        mb_mapping->tab_holding_registers[address] = data;
                        memcpy(response, query, query_length - mb_param->checksum_length);
                        resp_length = query_length;
                }
                break;
        case FC_FORCE_MULTIPLE_COILS: {
                int count = (query[offset+4] << 8) + query[offset+5];

                if ((address + count) > mb_mapping->nb_coil_status) {
                        printf("Illegal data address %0X in force_multiple_coils\n",
                               address + count);
                        resp_length = response_exception(mb_param, slave, function,
                                                         ILLEGAL_DATA_ADDRESS, response);
                } else {
                        resp_length = build_response_basis(mb_param, slave, function, response);
                        /* 4 to copy the coil address (2) and the quantity of coils */
                        memcpy(response + resp_length, query + resp_length, 4);
                        resp_length += 4;
                }
        }
                break;
        case FC_PRESET_MULTIPLE_REGISTERS: {
                int count = (query[offset+4] << 8) + query[offset+5];

                if ((address + count) > mb_mapping->nb_holding_registers) {
                        printf("Illegal data address %0X in preset_multiple_registers\n",
                               address + count);
                        resp_length = response_exception(mb_param, slave, function,
                                                         ILLEGAL_DATA_ADDRESS, response);
                } else {
                        resp_length = build_response_basis(mb_param, slave, function, response);
                        /* 4 to copy the address (2) and the no. of registers */
                        memcpy(response + resp_length, query + resp_length, 4);
                        resp_length += 4;
                }
        }
                break;
        case FC_READ_EXCEPTION_STATUS:
        case FC_REPORT_SLAVE_ID:
                printf("Not implemented\n");
                break;
        }

        modbus_send(mb_param, response, resp_length);
}

/* Listens any message on a socket or file descriptor.
   Returns:
   - 0 if OK, or a negative error number if the request fails
   - query, message received
   - query_length, length in bytes of the message */
int modbus_listen(modbus_param_t *mb_param, uint8_t *query, int *query_length)
{
        int ret;

        ret = receive_msg(mb_param, MSG_LENGTH_UNDEFINED, query, query_length);
        if (ret == 0) {
                ret = check_crc16(mb_param, query, *query_length);
        }
        
        return ret;
}

/* Reads IO status */
static int read_io_status(modbus_param_t *mb_param, int slave, int function,
                          int start_addr, int count, uint8_t *data_dest)
{
        int query_length;
        int query_ret;
        int response_ret;

        uint8_t query[MIN_QUERY_LENGTH];
        uint8_t response[MAX_MESSAGE_LENGTH];

        query_length = build_query_basis(mb_param, slave, function, 
                                         start_addr, count, query);

        query_ret = modbus_send(mb_param, query, query_length);
        if (query_ret > 0) {
                int i, temp, bit;
                int pos = 0;
                int processed = 0;
                int offset;
                int offset_length;

                response_ret = modbus_check_response(mb_param, query, response);
                offset = mb_param->header_length;

                offset_length = offset + response_ret;          
                for (i = offset; i < offset_length; i++) {
                        /* Shift reg hi_byte to temp */
                        temp = response[3 + i];
                        
                        for (bit = 0x01; (bit & 0xff) && (processed < count);) {
                                data_dest[pos++] = (temp & bit) ? TRUE : FALSE;
                                processed++;
                                bit = bit << 1;
                        }
                        
                }
        } else {
                response_ret = query_ret;
        }

        return response_ret;
}

/* Reads the boolean status of coils and sets the array elements
   in the destination to TRUE or FALSE. */
int read_coil_status(modbus_param_t *mb_param, int slave, int start_addr,
                     const int count, uint8_t *data_dest)
{
        int status;

        status = read_io_status(mb_param, slave, FC_READ_COIL_STATUS,
                                start_addr, count, data_dest);

        if (status > 0)
                status = count;
        
        return status;
}


/* Same as read_coil_status but reads the slaves input table */
int read_input_status(modbus_param_t *mb_param, int slave, int start_addr,
                      const int count, uint8_t *data_dest)
{
        int status;

        status = read_io_status(mb_param, slave, FC_READ_INPUT_STATUS,
                                start_addr, count, data_dest);

        if (status > 0)
                status = count;

        return status;
}

/* Reads the data from a modbus slave and put that data into an array */
static int read_registers(modbus_param_t *mb_param, int slave, int function,
                          int start_addr, int count, uint16_t *data_dest)
{
        int query_length;
        int status;
        int query_ret;
        uint8_t query[MIN_QUERY_LENGTH];

        query_length = build_query_basis(mb_param, slave, function, 
                                         start_addr, count, query);

        query_ret = modbus_send(mb_param, query, query_length);
        if (query_ret > 0)
                status = read_reg_response(mb_param, data_dest, query);
        else
                status = query_ret;
        
        return status;
}

/* Reads the holding registers in a slave and put the data into an
   array */
int read_holding_registers(modbus_param_t *mb_param, int slave,
                           int start_addr, int count, uint16_t *data_dest)
{
        int status;

        if (count > MAX_REGISTERS) {
                printf("WARNING Too many holding registers requested (%d > %d)\n",
                       count, MAX_REGISTERS);
                count = MAX_REGISTERS;
        }

        status = read_registers(mb_param, slave, FC_READ_HOLDING_REGISTERS,
                                start_addr, count, data_dest);
        return status;
}

/* Reads the input registers in a slave and put the data into
   an array */
int read_input_registers(modbus_param_t *mb_param, int slave,
                         int start_addr, int count, uint16_t *data_dest)
{
        int status;

        if (count > MAX_REGISTERS) {
                printf("WARNING Too many input registers requested (%d > %d)\n",
                       count, MAX_REGISTERS);
                count = MAX_REGISTERS;
        }

        status = read_registers(mb_param, slave, FC_READ_INPUT_REGISTERS,
                                start_addr, count, data_dest);

        return status;
}

/* Reads the response data from a slave and puts the data into an
   array */
static int read_reg_response(modbus_param_t *mb_param, uint16_t *data_dest,
                             uint8_t *query)
{
        uint8_t response[MAX_MESSAGE_LENGTH];
        int response_ret;
        int offset;
        int i;

        response_ret = modbus_check_response(mb_param, query, response);
        
        offset = mb_param->header_length;

        /* If response_ret is negative, the loop is jumped ! */
        for (i = 0; i < response_ret; i++) {
                /* shift reg hi_byte to temp OR with lo_byte */
                data_dest[i] = response[offset + 3 + (i << 1)] << 8 | 
                        response[offset + 4 + (i << 1)];    
        }
        
        return response_ret;
}

/* Gets the raw data from the input stream */
static int preset_response(modbus_param_t *mb_param, uint8_t *query) 
{
        int ret;
        uint8_t response[MAX_MESSAGE_LENGTH];

        ret = modbus_check_response(mb_param, query, response);

        return ret;
}

/* Sends a value to a register in a slave */
static int set_single(modbus_param_t *mb_param, int slave, int function,
                      int addr, int value)
{
        int status;
        int query_length;
        int query_ret;
        uint8_t query[MAX_MESSAGE_LENGTH];

        query_length = build_query_basis(mb_param, slave, function, 
                                         addr, value, query);

        query_ret = modbus_send(mb_param, query, query_length);
        if (query_ret > 0)
                status = preset_response(mb_param, query);
        else
                status = query_ret;

        return status;
}


/* Turns ON or OFF a single coil in the slave device */
int force_single_coil(modbus_param_t *mb_param, int slave,
                      int coil_addr, int state)
{
        int status;

        if (state)
                state = 0xFF00;

        status = set_single(mb_param, slave, FC_FORCE_SINGLE_COIL, coil_addr, state);

        return status;
}

/* Sets a value in one holding register in the slave device */
int preset_single_register(modbus_param_t *mb_param, int slave,
                           int reg_addr, int value)
{
        int status;

        status = set_single(mb_param, slave, FC_PRESET_SINGLE_REGISTER, reg_addr, value);

        return status;
}

/* Sets/resets the coils in the slave from an array in argument */
int force_multiple_coils(modbus_param_t *mb_param, int slave,
                         int start_addr, int nb_points,
                         uint8_t *data_src)
{
        int i;
        int byte_count;
        int query_length;
        int coil_check = 0;
        int status;
        int query_ret;
        int pos = 0;

        uint8_t query[MAX_MESSAGE_LENGTH];

        if (nb_points > MAX_STATUS) {
                printf("WARNING Writing to too many coils (%d > %d)\n",
                       nb_points, MAX_STATUS);
                nb_points = MAX_STATUS;
        }

        query_length = build_query_basis(mb_param, slave, FC_FORCE_MULTIPLE_COILS, 
                                         start_addr, nb_points, query);
        byte_count = (nb_points / 8) + ((nb_points % 8) ? 1 : 0);
        query[query_length++] = byte_count;

        for (i = 0; i < byte_count; i++) {
                int bit;

                bit = 0x01;
                query[query_length] = 0;

                while ((bit & 0xFF) && (coil_check++ < nb_points)) {
                        if (data_src[pos++])
                                query[query_length] |= bit;
                        else
                                query[query_length] &=~ bit;
                        
                        bit = bit << 1;
                }
                query_length++;
        }

        query_ret = modbus_send(mb_param, query, query_length);
        if (query_ret > 0)
                status = preset_response(mb_param, query);
        else
                status = query_ret;

        return status;
}

/* Copies the values in the slave from the array given in argument */
int preset_multiple_registers(modbus_param_t *mb_param, int slave,
                              int start_addr, int nb_points, uint16_t *data_src)
{
        int i;
        int query_length;
        int byte_count;
        int status;
        int query_ret;

        uint8_t query[MAX_MESSAGE_LENGTH];

        if (nb_points > MAX_REGISTERS) {
                printf("WARNING Trying to write to too many registers (%d > %d)\n",
                       nb_points, MAX_REGISTERS);
                nb_points = MAX_REGISTERS;
        }

        query_length = build_query_basis(mb_param, slave,
                                         FC_PRESET_MULTIPLE_REGISTERS, 
                                         start_addr, nb_points, query);
        byte_count = nb_points * 2;
        query[query_length++] = byte_count;

        for (i = 0; i < nb_points; i++) {
                query[query_length++] = data_src[i] >> 8;
                query[query_length++] = data_src[i] & 0x00FF;
        }

        query_ret = modbus_send(mb_param, query, query_length);
        if (query_ret > 0)
                status = preset_response(mb_param, query);
        else
                status = query_ret;

        return status;
}

/* Returns the slave id! */
int report_slave_id(modbus_param_t *mb_param, int slave, 
                    uint8_t *data_dest)
{
        int query_length;
        int query_ret;
        int response_ret;

        uint8_t query[MIN_QUERY_LENGTH];
        uint8_t response[MAX_MESSAGE_LENGTH];
        
        query_length = build_query_basis(mb_param, slave, FC_REPORT_SLAVE_ID, 
                                         0, 0, query);
        
        /* start_addr and count are not used */
        query_length -= 4;
        
        query_ret = modbus_send(mb_param, query, query_length);
        if (query_ret > 0) {
                int i;
                int offset;
                int offset_length;

                /* Byte count, slave id, run indicator status,
                   additional data */
                response_ret = modbus_check_response(mb_param, query, response);
                
                offset = mb_param->header_length;
                offset_length = offset + response_ret;

                for (i = offset; i < offset_length; i++)
                        data_dest[i] = response[i];
        } else {
                response_ret = query_ret;
        }

        return response_ret;
}

/* Initializes the modbus_param_t structure for RTU
   - device: "/dev/ttyS0"
   - baud:   9600, 19200, 57600, 115200, etc
   - parity: "even", "odd" or "none" 
   - data_bits: 5, 6, 7, 8 
   - stop_bits: 1, 2
*/
void modbus_init_rtu(modbus_param_t *mb_param, char *device,
                     int baud, char *parity, int data_bit,
                     int stop_bit)
{
        memset(mb_param, 0, sizeof(modbus_param_t));
        strcpy(mb_param->device, device);
        mb_param->baud = baud;
        strcpy(mb_param->parity, parity);
        mb_param->debug = FALSE;
        mb_param->data_bit = data_bit;
        mb_param->stop_bit = stop_bit;
        mb_param->type_com = RTU;
        mb_param->header_length = HEADER_LENGTH_RTU;
        mb_param->checksum_length = CHECKSUM_LENGTH_RTU;
}

/* Initializes the modbus_param_t structure for TCP.
   - ip : "192.168.0.5" 
   - port : 1099

   Set the port to MODBUS_TCP_DEFAULT_PORT to use the default one
   (502). It's convenient to use a port number greater than or equal
   to 1024 because it's not necessary to be root to use this port
   number.
*/
void modbus_init_tcp(modbus_param_t *mb_param, char *ip, int port)
{
        memset(mb_param, 0, sizeof(modbus_param_t));
        strncpy(mb_param->ip, ip, sizeof(char)*16);
        mb_param->port = port;
        mb_param->type_com = TCP;
        mb_param->header_length = HEADER_LENGTH_TCP;
        mb_param->checksum_length = CHECKSUM_LENGTH_TCP;
        mb_param->error_handling = FLUSH_OR_RECONNECT_ON_ERROR;
}

/* By default, the error handling mode used is FLUSH_OR_RECONNECT_ON_ERROR.

   With FLUSH_OR_RECONNECT_ON_ERROR, the library will flush to I/O
   port in RTU mode or attempt an immediate reconnection which may
   hang for several seconds if the network to the remote target unit
   is down in TCP mode.

   With NOP_ON_ERROR, it is expected that the application will
   check for error returns and deal with them as necessary.
*/
void modbus_set_error_handling(modbus_param_t *mb_param, error_handling_t error_handling)
{
        if (error_handling == FLUSH_OR_RECONNECT_ON_ERROR ||
            error_handling == NOP_ON_ERROR) {
                mb_param->error_handling = error_handling;
        } else {
                printf("Invalid setting for error handling (not changed)\n");
        }
}


/* Sets up a serial port for RTU communications */
static int modbus_connect_rtu(modbus_param_t *mb_param)
{
        struct termios tios;
        speed_t speed;

        if (mb_param->debug) {
                printf("Opening %s at %d bauds (%s)\n",
                       mb_param->device, mb_param->baud, mb_param->parity);
        }

        /* The O_NOCTTY flag tells UNIX that this program doesn't want
           to be the "controlling terminal" for that port. If you
           don't specify this then any input (such as keyboard abort
           signals and so forth) will affect your process

           Timeouts are ignored in canonical input mode or when the
           NDELAY option is set on the file via open or fcntl */
        mb_param->fd = open(mb_param->device, O_RDWR | O_NOCTTY | O_NDELAY);
        if (mb_param->fd < 0) {
                perror("open");
                printf("ERROR Can't open the device %s (errno %d)\n",
                       mb_param->device, errno);
                return -1;
        }

        /* Save */
        tcgetattr(mb_param->fd, &(mb_param->old_tios));

        memset(&tios, 0, sizeof(struct termios));
        
        /* C_ISPEED     Input baud (new interface)
           C_OSPEED     Output baud (new interface)
        */
        switch (mb_param->baud) {
        case 110:
                speed = B110;
                break;
        case 300:
                speed = B300;
                break;
        case 600:
                speed = B600;
                break;
        case 1200:
                speed = B1200;
                break;
        case 2400:
                speed = B2400;
                break;
        case 4800:
                speed = B4800;
                break;
        case 9600: 
                speed = B9600;
                break;
        case 19200:
                speed = B19200;
                break;
        case 38400:
                speed = B38400;
                break;
        case 57600:
                speed = B57600;
                break;
        case 115200:
                speed = B115200;
                break;
        default:
                speed = B9600;
                printf("WARNING Unknown baud rate %d for %s (B9600 used)\n",
                       mb_param->baud, mb_param->device);
        }

        /* Set the baud rate */
        if ((cfsetispeed(&tios, speed) < 0) ||
            (cfsetospeed(&tios, speed) < 0)) {
                perror("cfsetispeed/cfsetospeed\n");
                return -1;
        }
        
        /* C_CFLAG      Control options
           CLOCAL       Local line - do not change "owner" of port
           CREAD        Enable receiver
        */
        tios.c_cflag |= (CREAD | CLOCAL);
        /* CSIZE, HUPCL, CRTSCTS (hardware flow control) */

        /* Set data bits (5, 6, 7, 8 bits)
           CSIZE        Bit mask for data bits
        */
        tios.c_cflag &= ~CSIZE;
        switch (mb_param->data_bit) {
        case 5:
                tios.c_cflag |= CS5;
                break;
        case 6:
                tios.c_cflag |= CS6;
                break;
        case 7:
                tios.c_cflag |= CS7;
                break;
        case 8:
        default:
                tios.c_cflag |= CS8;
                break;
        }

        /* Stop bit (1 or 2) */
        if (mb_param->stop_bit == 1)
                tios.c_cflag &=~ CSTOPB;
        else /* 2 */
                tios.c_cflag |= CSTOPB;

        /* PARENB       Enable parity bit
           PARODD       Use odd parity instead of even */
        if (strncmp(mb_param->parity, "none", 4) == 0) {
                tios.c_cflag &=~ PARENB;
        } else if (strncmp(mb_param->parity, "even", 4) == 0) {
                tios.c_cflag |= PARENB;
                tios.c_cflag &=~ PARODD;
        } else {
                /* odd */
                tios.c_cflag |= PARENB;
                tios.c_cflag |= PARODD;
        }
        
        /* Read the man page of termios if you need more information. */

        /* This field isn't used on POSIX systems 
           tios.c_line = 0; 
        */

        /* C_LFLAG      Line options 

           ISIG Enable SIGINTR, SIGSUSP, SIGDSUSP, and SIGQUIT signals
           ICANON       Enable canonical input (else raw)
           XCASE        Map uppercase \lowercase (obsolete)
           ECHO Enable echoing of input characters
           ECHOE        Echo erase character as BS-SP-BS
           ECHOK        Echo NL after kill character
           ECHONL       Echo NL
           NOFLSH       Disable flushing of input buffers after
           interrupt or quit characters
           IEXTEN       Enable extended functions
           ECHOCTL      Echo control characters as ^char and delete as ~?
           ECHOPRT      Echo erased character as character erased
           ECHOKE       BS-SP-BS entire line on line kill
           FLUSHO       Output being flushed
           PENDIN       Retype pending input at next read or input char
           TOSTOP       Send SIGTTOU for background output

           Canonical input is line-oriented. Input characters are put
           into a buffer which can be edited interactively by the user
           until a CR (carriage return) or LF (line feed) character is
           received.  

           Raw input is unprocessed. Input characters are passed
           through exactly as they are received, when they are
           received. Generally you'll deselect the ICANON, ECHO,
           ECHOE, and ISIG options when using raw input
        */

        /* Raw input */
        tios.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);

        /* C_IFLAG      Input options 

           Constant     Description
           INPCK        Enable parity check
           IGNPAR       Ignore parity errors
           PARMRK       Mark parity errors
           ISTRIP       Strip parity bits
           IXON Enable software flow control (outgoing)
           IXOFF        Enable software flow control (incoming)
           IXANY        Allow any character to start flow again
           IGNBRK       Ignore break condition
           BRKINT       Send a SIGINT when a break condition is detected
           INLCR        Map NL to CR
           IGNCR        Ignore CR
           ICRNL        Map CR to NL
           IUCLC        Map uppercase to lowercase
           IMAXBEL      Echo BEL on input line too long
        */
        if (strncmp(mb_param->parity, "none", 4) == 0) {
                tios.c_iflag &= ~INPCK;
        } else {
                tios.c_iflag |= INPCK;
        }

        /* Software flow control is disabled */
        tios.c_iflag &= ~(IXON | IXOFF | IXANY);
        
        /* C_OFLAG      Output options
           OPOST        Postprocess output (not set = raw output)
           ONLCR        Map NL to CR-NL

           ONCLR ant others needs OPOST to be enabled
        */         

        /* Raw ouput */
        tios.c_oflag &=~ OPOST;

        /* C_CC         Control characters 
           VMIN         Minimum number of characters to read
           VTIME        Time to wait for data (tenths of seconds)

           UNIX serial interface drivers provide the ability to
           specify character and packet timeouts. Two elements of the
           c_cc array are used for timeouts: VMIN and VTIME. Timeouts
           are ignored in canonical input mode or when the NDELAY
           option is set on the file via open or fcntl.

           VMIN specifies the minimum number of characters to read. If
           it is set to 0, then the VTIME value specifies the time to
           wait for every character read. Note that this does not mean
           that a read call for N bytes will wait for N characters to
           come in. Rather, the timeout will apply to the first
           character and the read call will return the number of
           characters immediately available (up to the number you
           request).

           If VMIN is non-zero, VTIME specifies the time to wait for
           the first character read. If a character is read within the
           time given, any read will block (wait) until all VMIN
           characters are read. That is, once the first character is
           read, the serial interface driver expects to receive an
           entire packet of characters (VMIN bytes total). If no
           character is read within the time allowed, then the call to
           read returns 0. This method allows you to tell the serial
           driver you need exactly N bytes and any read call will
           return 0 or N bytes. However, the timeout only applies to
           the first character read, so if for some reason the driver
           misses one character inside the N byte packet then the read
           call could block forever waiting for additional input
           characters.

           VTIME specifies the amount of time to wait for incoming
           characters in tenths of seconds. If VTIME is set to 0 (the
           default), reads will block (wait) indefinitely unless the
           NDELAY option is set on the port with open or fcntl.
        */
        /* Unused because we use open with the NDELAY option */
        tios.c_cc[VMIN] = 0;
        tios.c_cc[VTIME] = 0;

        if (tcsetattr(mb_param->fd, TCSANOW, &tios) < 0) {
                perror("tcsetattr\n");
                return -1;
        }

        return 0;
}

/* Establishes a modbus TCP connection with a modbus slave */
static int modbus_connect_tcp(modbus_param_t *mb_param)
{
        int ret;
        int option;
        struct sockaddr_in addr;

        addr.sin_family = AF_INET;
        addr.sin_port = htons(mb_param->port);
        addr.sin_addr.s_addr = inet_addr(mb_param->ip);

        mb_param->fd = socket(AF_INET, SOCK_STREAM, 0);
        if (mb_param->fd < 0) {
                return mb_param->fd;
        }

        /* Set the TCP no delay flag */
        /* SOL_TCP = IPPROTO_TCP */
        option = 1;
        ret = setsockopt(mb_param->fd, IPPROTO_TCP, TCP_NODELAY,
                         (const void *)&option, sizeof(int));
        if (ret < 0) {
                perror("setsockopt");
                close(mb_param->fd);
                return ret;
        }

        /* Set the IP low delay option */
        option = IPTOS_LOWDELAY;
        ret = setsockopt(mb_param->fd, IPPROTO_TCP, IP_TOS,
                         (const void *)&option, sizeof(int));
        if (ret < 0) {
                perror("setsockopt");
                close(mb_param->fd);
                return ret;
        }

        if (mb_param->debug) {
                printf("Connecting to %s\n", mb_param->ip);
        }
        
        ret = connect(mb_param->fd, (struct sockaddr *)&addr,
                      sizeof(struct sockaddr_in));
        if (ret < 0) {
                perror("connect");
                close(mb_param->fd);
                return ret;
        }

        return 0;
}

/* Establishes a modbus connexion */
int modbus_connect(modbus_param_t *mb_param)
{
        int ret;

        if (mb_param->type_com == RTU)
                ret = modbus_connect_rtu(mb_param);
        else
                ret = modbus_connect_tcp(mb_param);

        return ret;
}

/* Closes the file descriptor in RTU mode */
static void modbus_close_rtu(modbus_param_t *mb_param)
{
        if (tcsetattr(mb_param->fd, TCSANOW, &(mb_param->old_tios)) < 0)
                perror("tcsetattr");
        
        close(mb_param->fd);
}

/* Closes the network connection and socket in TCP mode */
static void modbus_close_tcp(modbus_param_t *mb_param)
{
        shutdown(mb_param->fd, SHUT_RDWR);
        close(mb_param->fd);
}

/* Closes a modbus connection */
void modbus_close(modbus_param_t *mb_param)
{
        if (mb_param->type_com == RTU)
                modbus_close_rtu(mb_param);
        else
                modbus_close_tcp(mb_param);
}

/* Activates the debug messages */
void modbus_set_debug(modbus_param_t *mb_param, int boolean)
{
        mb_param->debug = boolean;
}

/* Allocates 4 arrays to store coils, input status, input registers and
   holding registers. The pointers are stored in modbus_mapping structure. 

   Returns: TRUE if ok, FALSE on failure
*/
int modbus_mapping_new(modbus_mapping_t *mb_mapping,
                       int nb_coil_status, int nb_input_status,
                       int nb_holding_registers, int nb_input_registers)
{
        /* 0X */
        mb_mapping->nb_coil_status = nb_coil_status;
        mb_mapping->tab_coil_status = (uint8_t *) malloc(nb_coil_status * sizeof(uint8_t));
        memset(mb_mapping->tab_coil_status, 0, nb_coil_status * sizeof(uint8_t));
        if (mb_mapping->tab_coil_status == NULL)
                return FALSE;
        
        /* 1X */
        mb_mapping->nb_input_status = nb_input_status;
        mb_mapping->tab_input_status = (uint8_t *) malloc(nb_input_status * sizeof(uint8_t));
        memset(mb_mapping->tab_input_status, 0, nb_input_status * sizeof(uint8_t));
        if (mb_mapping->tab_input_status == NULL) {
                free(mb_mapping->tab_coil_status);
                return FALSE;
        }

        /* 4X */
        mb_mapping->nb_holding_registers = nb_holding_registers;
        mb_mapping->tab_holding_registers = (uint16_t *) malloc(nb_holding_registers * sizeof(uint16_t));
        memset(mb_mapping->tab_holding_registers, 0, nb_holding_registers * sizeof(uint16_t));
        if (mb_mapping->tab_holding_registers == NULL) {
                free(mb_mapping->tab_coil_status);
                free(mb_mapping->tab_input_status);
                return FALSE;
        }

        /* 3X */
        mb_mapping->nb_input_registers = nb_input_registers;
        mb_mapping->tab_input_registers = (uint16_t *) malloc(nb_input_registers * sizeof(uint16_t));
        memset(mb_mapping->tab_input_registers, 0, nb_input_registers * sizeof(uint16_t));
        if (mb_mapping->tab_input_registers == NULL) {
                free(mb_mapping->tab_coil_status);
                free(mb_mapping->tab_input_status);
                free(mb_mapping->tab_holding_registers);
                return FALSE;
        }

        return TRUE;
}

/* Frees the 4 arrays */
void modbus_mapping_free(modbus_mapping_t *mb_mapping)
{
        free(mb_mapping->tab_coil_status);
        free(mb_mapping->tab_input_status);
        free(mb_mapping->tab_holding_registers);
        free(mb_mapping->tab_input_registers);
}

/* Listens for any query from a modbus master in TCP */
int modbus_init_listen_tcp(modbus_param_t *mb_param)
{
        int ret;
        int new_socket;
        struct sockaddr_in addr;
        socklen_t addrlen;

        addr.sin_family = AF_INET;
        /* If the modbus port is < to 1024, we need the setuid root. */
        addr.sin_port = htons(mb_param->port);
        addr.sin_addr.s_addr = INADDR_ANY;
        memset(&(addr.sin_zero), '\0', 8);

        new_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
        if (new_socket < 0) {
                perror("socket");
                exit(1);
        } else {
                printf("Socket OK\n");
        }

        ret = bind(new_socket, (struct sockaddr *)&addr,
                   sizeof(struct sockaddr_in));
        if (ret < 0) {
                perror("bind");
                close(new_socket);
                exit(1);
        } else {
                printf("Bind OK\n");
        }

        ret = listen(new_socket, 1);
        if (ret != 0) {
                perror("listen");
                close(new_socket);
                exit(1);
        } else {
                printf("Listen OK\n");
        }

        addrlen = sizeof(struct sockaddr_in);
        mb_param->fd = accept(new_socket, (struct sockaddr *)&addr, &addrlen);
        if (ret < 0) {
                perror("accept");
                close(new_socket);
                new_socket = 0;
                exit(1);
        } else {
                printf("The client %s is connected\n", 
                       inet_ntoa(addr.sin_addr));
        }

        return new_socket;
}

/** Utils **/

/* Sets many inputs/coils from a single byte value (all 8 bits of the
   byte value are setted) */
void set_bits_from_byte(uint8_t *dest, int address, const uint8_t value)
{
        int i;

        for (i=0; i<8; i++) {
                dest[address+i] = (value & (1 << i)) ? ON : OFF;
        }
}

/* Sets many inputs/coils from a table of bytes (only the bits between
   address and address + nb_points are setted) */
void set_bits_from_bytes(uint8_t *dest, int address, int nb_points, const uint8_t tab_byte[])
{
        int i;
        int shift = 0;

        for (i=address; i < address + nb_points; i++) {
                dest[i] = tab_byte[(i - address) / 8] & (1 << shift) ? ON : OFF;
                /* gcc doesn't like: shift = (++shift) % 8; */
                shift++;
                shift %= 8;
        }
}

/* Gets the byte value from many inputs/coils.
   To obtain a full byte, set nb_points to 8. */
uint8_t get_byte_from_bits(const uint8_t *src, int address, int nb_bits)
{
        int i;
        uint8_t value = 0;
 
        if (nb_bits > 8) {
                printf("Error: nb_bits is too big\n");
                nb_bits = 8;
        }

        for (i=0; i<nb_bits; i++) {
                value |= (src[address+i] << i);
        }
        
        return value;
}