Variables start_addr and count were read from query_packet using function mb_ntoh_safe. It looks like some compilers change the pointer alignment if the first byte starts at an odd address. Because mb_ntoh_safe uses pointers slave address and count (number of registers) were not read correctly from the buffer when several modbus slaves were present in network. In this temporary solution pointer aritmetics is replaced by simple 256 multiplication.
/*
* Copyright (c) 2001,2016 Mario de Sousa (msousa@fe.up.pt)
*
* This file is part of the Modbus library for Beremiz and matiec.
*
* This Modbus 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 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
* General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this Modbus library. If not, see <http://www.gnu.org/licenses/>.
*
* This code is made available on the understanding that it will not be
* used in safety-critical situations without a full and competent review.
*/
#ifndef MODBUS_LAYER1_H
#define MODBUS_LAYER1_H
#include <time.h> /* struct timespec data type */
#include "mb_types.h" /* get the data types */
#include "mb_addr.h" /* get definitions of common variable types */
/* Define max registers and bits */
#define MAX_READ_BITS 2000 /* Functions 0x01 and 0x02 */
#define MAX_READ_REGS 125 /* Functions 0x03 and 0x04 */
#define MAX_WRITE_COILS 1968 /* Function 0x0F */
#define MAX_WRITE_REGS 123 /* Function 0x10 */
/* Declare TCP layer1 functions */
#define modbus_write modbus_tcp_write
#define modbus_read modbus_tcp_read
#define modbus_init modbus_tcp_init
#define modbus_done modbus_tcp_done
#define modbus_connect modbus_tcp_connect
#define modbus_listen modbus_tcp_listen
#define modbus_close modbus_tcp_close
#define modbus_silence_init modbus_tcp_silence_init
#define modbus_get_min_timeout modbus_tcp_get_min_timeout
#include "mb_layer1_prototypes.h"
#undef modbus_write
#undef modbus_read
#undef modbus_init
#undef modbus_done
#undef modbus_connect
#undef modbus_listen
#undef modbus_close
#undef modbus_silence_init
#undef modbus_get_min_timeout
/* Declare RTU layer1 functions */
#define modbus_write modbus_rtu_write
#define modbus_read modbus_rtu_read
#define modbus_init modbus_rtu_init
#define modbus_done modbus_rtu_done
#define modbus_connect modbus_rtu_connect
#define modbus_listen modbus_rtu_listen
#define modbus_close modbus_rtu_close
#define modbus_silence_init modbus_rtu_silence_init
#define modbus_get_min_timeout modbus_rtu_get_min_timeout
#include "mb_layer1_prototypes.h"
#undef modbus_write
#undef modbus_read
#undef modbus_init
#undef modbus_done
#undef modbus_connect
#undef modbus_listen
#undef modbus_close
#undef modbus_silence_init
#undef modbus_get_min_timeout
/* Declare ASCII layer1 functions */
#define modbus_write modbus_ascii_write
#define modbus_read modbus_ascii_read
#define modbus_init modbus_ascii_init
#define modbus_done modbus_ascii_done
#define modbus_connect modbus_ascii_connect
#define modbus_listen modbus_ascii_listen
#define modbus_close modbus_ascii_close
#define modbus_silence_init modbus_ascii_silence_init
#define modbus_get_min_timeout modbus_ascii_get_min_timeout
#include "mb_layer1_prototypes.h"
#undef modbus_write
#undef modbus_read
#undef modbus_init
#undef modbus_done
#undef modbus_connect
#undef modbus_listen
#undef modbus_close
#undef modbus_silence_init
#undef modbus_get_min_timeout
#define modbus_write (*modbus_write )
#define modbus_read (*modbus_read )
#define modbus_init (*modbus_init )
#define modbus_done (*modbus_done )
#define modbus_connect (*modbus_connect )
#define modbus_listen (*modbus_listen )
#define modbus_close (*modbus_close )
#define modbus_silence_init (*modbus_silence_init )
#define modbus_get_min_timeout (*modbus_get_min_timeout)
typedef struct {
#include "mb_layer1_prototypes.h"
} layer1_funct_ptr_t;
#undef modbus_write
#undef modbus_read
#undef modbus_init
#undef modbus_done
#undef modbus_connect
#undef modbus_listen
#undef modbus_close
#undef modbus_silence_init
#undef modbus_get_min_timeout
extern layer1_funct_ptr_t fptr_[4];
#endif /* MODBUS_LAYER1_H */