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.
*/
/* mb_slave.h */
#ifndef MODBUS_SLAVE_H
#define MODBUS_SLAVE_H
#include <time.h> /* struct timespec data structure */
#include "mb_types.h" /* get the data types */
#include "mb_addr.h" /* get definition of common variable types and error codes */
/* Initialise the Modbus Library to work as Slave/Server only */
int mb_slave_init(int nd_count);
/* Shut down the Modbus Library */
int mb_slave_done(void);
/* Create a new slave/server...
*
* This function creates a new node used to:
* - accept connection requests (TCP version)
* - receive frames from masters (RTU and ASCII versions)
*
* The type of address (naf_tcp, naf_rtu, naf_ascii) will specify the lower
* layer of modbus that will be used by the newly opened node.
*/
int mb_slave_new(node_addr_t node_addr);
/* close a node crreated by mb_slave_new() */
int mb_slave_close(int nd);
/***********************************************/
/***********************************************/
/** **/
/** Run the slave **/
/** **/
/***********************************************/
/***********************************************/
/* The following functions must return:
* -2 on attempt to read invalid address
* -1 on all other errors...
* 0 on success.
*
* Start_addr may start from 0, to 65535!
* In other words, we use 0 based addressing!
*/
typedef struct {
int (*read_inbits) (void *arg, u16 start_addr, u16 bit_count, u8 *data_bytes); /* bits are packed into bytes... */
int (*read_outbits) (void *arg, u16 start_addr, u16 bit_count, u8 *data_bytes); /* bits are packed into bytes... */
int (*write_outbits) (void *arg, u16 start_addr, u16 bit_count, u8 *data_bytes); /* bits are packed into bytes... */
int (*read_inwords) (void *arg, u16 start_addr, u16 word_count, u16 *data_words);
int (*read_outwords) (void *arg, u16 start_addr, u16 word_count, u16 *data_words);
int (*write_outwords)(void *arg, u16 start_addr, u16 word_count, u16 *data_words);
void *arg;
} mb_slave_callback_t;
/* Execute the Slave and process requests coming from masters...
* This function enters an infinite loop wating for new connection requests,
* and for modbus requests over previoulsy open connections...
*
* The frames are read from:
* - the node descriptor nd, if nd >= 0
* When using TCP, if the referenced node nd was created to listen for new connections
* [mb_slave_listen()], then this function will also reply to Modbus data requests arriving
* on other nodes that were created as a consequence of accepting connections requests to
* the referenced node nd.
* All other nodes are ignored!
*
* - any valid and initialised TCP node descriptor, if nd = -1
* In this case, will also accept connection requests arriving from a previously
* created node to listen for new connection requests [mb_slave_listen() ].
* NOTE: (only avaliable if using TCP)
*
* slaveid identifies the address (RTU and ASCII) or slaveid (TCP) that we implement.
* Any requests that we receive sent with a slaveid different
* than the one specified, and also different to 0, will be silently ignored!
* Whatever the slaveid specified, we always reply to requests
* to slaveid 0 (the modbus broadcast address).
* Calling this function with a slaveid of 0 means to ignore this
* parameter and to reply to all requests (whatever the slaveid
* used in the request). This should mostly be used by TCP servers...
*/
int mb_slave_run(int nd, mb_slave_callback_t callback_functions, u8 slaveid);
#endif /* MODBUS_SLAVE_H */