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) 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 SIN_UTIL_H
#define SIN_UTIL_H
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
/* Create a socket for the IP protocol family, and connect to remote host. */
int sin_connsock(const char *host, const char *service, const char *protocol);
/* Create a socket for the IP protocol family, and bind to local host's port. */
int sin_bindsock(const char *host, const char *service, const char *protocol);
/* Initialize a in_addr structure */
int sin_initaddr(struct sockaddr_in *sin,
const char *host, int allow_null_host, // 1 => allow host NULL, "" or "*" -> INADDR_ANY
const char *service, int allow_null_serv, // 1 => allow serivce NULL or "" -> port = 0
const char *protocol);
#endif