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 MB_UTIL_H
#define MB_UTIL_H
/* This file has constants related to the modbus protocol */
/*
* Some of these constants are specific to the layer two protocols
* (i.e. master and slave), while others are specific of the
* layer one protocols (i.e. rtu, ascii, tcp).
*
* a) Unfortunately, due to the nature of the modbus protocol, that does not
* include a frame size field in the layer 1 frame (see note 1), and the
* fact that we are implementing it at the user level, the implementation
* of some layer 1 protocols need to know the content of the layer 2 protocol
* in order to determine the size of the frame.
*
* b) The layer two message formats are in fact the same, just reversing the role
* being played (master or slave).
*
* Bothe a) and b) mean we need the same modbus protocol constants in several files.
* It ends up making more sense to put them all together in a single file, which
* makes updating easier, even though we are trying to strictly seperate the layer 1
* and layer 2 protocols.
*
*
*
* Notes:
* (1) There is no layer 1 field with the frame size, nevertheless this
* size can be determined indirectly due to timing restrictions on the rtu
* protocol. Unfortunately, due to the fact that we are implementing
* it at the user level, we are not guaranteed to detect these timings
* correctly, and therefore have to rely on layer 2 protocol info to
* determine the frame size.
* For the ascii protocol, the frame size is determined indirectly by
* a frame header and tail, so we do not use layer 2 protocol info.
*/
/* Layer 2 Frame Structure... */
/* Valid for both master and slave protocols */
#define L2_FRAME_HEADER_LENGTH 6
#define L2_FRAME_BYTECOUNT_LENGTH 1
#define L2_FRAME_DATABYTES_LENGTH 255
#define MAX_L2_FRAME_LENGTH (L2_FRAME_HEADER_LENGTH + L2_FRAME_BYTECOUNT_LENGTH + \
L2_FRAME_DATABYTES_LENGTH)
#define L2_FRAME_SLAVEID_OFS 0
#define L2_FRAME_FUNCTION_OFS 1
/* Layer 1 - Ascii Frame sizes... */
#define L2_TO_ASC_CODING 2 /* number of ascii bytes used to code a Layer 2 frame byte */
#define ASC_FRAME_HEADER_LENGTH 1
#define ASC_FRAME_HEADER ':'
#define ASC_FRAME_TAIL_LENGTH 2
#define ASC_FRAME_TAIL_0 '\13' /* 'CR' */
#define ASC_FRAME_TAIL_1 '\10' /* 'LF' */
#define ASC_FRAME_LRC_LENGTH 2
/* Layer 1 - RTU Frame sizes... */
#define RTU_FRAME_CRC_LENGTH 2
/* Layer 1 - TCP Frame sizes... */
#define TCP_HEADER_LENGTH 6
/* Global Frame sizes */
#define MAX_RTU_FRAME_LENGTH MAX_L2_FRAME_LENGTH + RTU_FRAME_CRC_LENGTH
#define MAX_ASC_FRAME_LENGTH ((MAX_L2_FRAME_LENGTH * L2_TO_ASC_CODING) + \
ASC_FRAME_HEADER_LENGTH + ASC_FRAME_TAIL_LENGTH + \
ASC_FRAME_LRC_LENGTH)
/* Modbus Exception codes */
#define ERR_ILLEGAL_FUNCTION 0x01
#define ERR_ILLEGAL_DATA_ADDRESS 0x02
#define ERR_ILLEGAL_DATA_VALUE 0x03
#define ERR_SLAVE_DEVICE_FAILURE 0x04
#define ERR_ACKNOWLEDGE 0x05
#define ERR_SLAVE_DEVICE_BUSY 0x06
#define ERR_NEGATIVE_ACKNOWLEDGE 0x07
#define ERR_MEMORY_PARITY_ERROR 0x08
#define ERR_GATEWAY_PATH_UNAVAILABLE 0x0A
#define ERR_GATEWAY_TARGET_DEVICE_FAILED_TO_RESPOND 0x0B
#endif /* MB_UTIL_H */