FreeModbus开源协议栈的移植和详解（三）- RTU协议代码分析

最新推荐文章于 2025-05-30 09:39:05 发布

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最新推荐文章于 2025-05-30 09:39:05 发布

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分类专栏： FreeModbus 文章标签： FreeModbus 嵌入式单片机通信工控

本文链接：https://blog.youkuaiyun.com/u014100102/article/details/90543437

本文深入分析了FreeModbus开源协议栈中的mbrtu.c文件，详细解释了数据接收、发送、UART初始化、中断处理等关键函数。超时时间配置与波特率密切相关，接收和发送函数确保数据的正确性。mbrtu.c实现了Modbus-RTU协议栈，是连接硬件与协议的关键部分。

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概述

上篇文章分析了mb.c文件，我们知道，mb.c只是实现modbus协议的一个框架，具体的RTU、ASCII和TCP相关的代码再具体的文件夹中。这里我们以使用比较多的RTU为例，来分析一下RTU的实现。

一、RTU文件夹的文件

rtu文件夹下有四个文件，其说明如下：

文件名称	说明
mbcrc.c	这个文件只包含一个函数，就是标准的CRC16校验函数
mbcrc.h	包含CRC校验函数的函数声明
mbrtu.c	实现RTU协议的具体函数，rtu协议相关的实现函数都在这个文件中
mbrtu.h	头文件，包含rtu函数的声明

这里我们主要分析mbrtu.c文件，其他文件都比较简单。

二、mbrtu.c文件

先贴上代码，再一一说明。

/* 
 * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
 * Copyright (c) 2006-2018 Christian Walter <cwalter@embedded-solutions.at>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

/* ----------------------- System includes ----------------------------------*/
#include "stdlib.h"
#include "string.h"

/* ----------------------- Platform includes --------------------------------*/
#include "port.h"

/* ----------------------- Modbus includes ----------------------------------*/
#include "mb.h"
#include "mbrtu.h"
#include "mbframe.h"

#include "mbcrc.h"
#include "mbport.h"

/* ----------------------- Defines ------------------------------------------*/
#define MB_SER_PDU_SIZE_MIN     4       /*!< Minimum size of a Modbus RTU frame. */
#define MB_SER_PDU_SIZE_MAX     256     /*!< Maximum size of a Modbus RTU frame. */
#define MB_SER_PDU_SIZE_CRC     2       /*!< Size of CRC field in PDU. */
#define MB_SER_PDU_ADDR_OFF     0       /*!< Offset of slave address in Ser-PDU. */
#define MB_SER_PDU_PDU_OFF      1       /*!< Offset of Modbus-PDU in Ser-PDU. */

/* ----------------------- Type definitions ---------------------------------*/
typedef enum
{
   
   
    STATE_RX_INIT,              /*!< Receiver is in initial state. */
    STATE_RX_IDLE,              /*!< Receiver is in idle state. */
    STATE_RX_RCV,               /*!< Frame is beeing received. */
    STATE_RX_ERROR              /*!< If the frame is invalid. */
} eMBRcvState;

typedef enum
{
   
   
    STATE_TX_IDLE,              /*!< Transmitter is in idle state. */
    STATE_TX_XMIT               /*!< Transmitter is in transfer state. */
} eMBSndState;

/* ----------------------- Static variables ---------------------------------*/
static volatile eMBSndState eSndState;
static volatile eMBRcvState eRcvState;

volatile UCHAR  ucRTUBuf[MB_SER_PDU_SIZE_MAX];

static volatile UCHAR *pucSndBufferCur;
static volatile USHORT usSndBufferCount;

static volatile USHORT usRcvBufferPos;

/* ----------------------- Start implementation -----------------------------*/
eMBErrorCode
eMBRTUInit( UCHAR ucSlaveAddress, UCHAR ucPort, ULONG ulBaudRate, eMBParity eParity )
{