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) 2002,2016 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_LAYER2_H
#define MODBUS_LAYER2_H
#include <time.h> /* struct timespec data type */
//#include <sys/socket.h>
//#include <netinet/in.h>
#include <netinet/ip.h> /* superset of previous */ // Required for INADDR_ANY
/* Library Error codes */
#define PORT_FAILURE -101
#define INTERNAL_ERROR -102
#define TIMEOUT -103
#define INVALID_FRAME -104
#define MODBUS_ERROR -105
/* NOTE: Modbus error codes are defined in mb_util.h */
typedef enum {optimize_speed, optimize_size} optimization_t;
typedef enum {
naf_ascii,
naf_rtu,
naf_tcp,
} node_addr_family_t;
typedef struct {
const char *host;
const char *service;
int close_on_silence;
} node_addr_tcp_t;
typedef struct {
const char *device;
int baud; /* plain baud rate, eg 2400; zero for the default 9600 */
int parity; /* 0 for none, 1 for odd, 2 for even */
int data_bits;
int stop_bits;
int ignore_echo; /* 1 => ignore echo; 0 => do not ignore echo */
} node_addr_rtu_t;
typedef node_addr_rtu_t node_addr_ascii_t;
typedef union {
node_addr_ascii_t ascii;
node_addr_rtu_t rtu;
node_addr_tcp_t tcp;
} node_addr_common_t;
typedef struct {
node_addr_family_t naf;
node_addr_common_t addr;
} node_addr_t;
#endif /* MODBUS_LAYER2_H */