【嵌入式】Libmodbus源码分析(一)-类型和结构体

﹏ヽ暗。殇╰゛Y 2023-01-20 08:06 30阅读 0赞

## 00. 目录 ##

### 文章目录 ###

*   *  00. 目录
     *  01. 常见类型声明
     *  02. 常量声明
     *  03. \_modbus结构体声明
     *  04. modbus\_backend\_t结构体声明
     *  05. modbus\_mapping\_t结构体声明
     *  06. 附录

## 01. 常见类型声明 ##

便于理解和跨平台使用。

stdint.h内容如下：

//
    // stdint.h
    //
    // Copyright (c) Microsoft Corporation. All rights reserved.
    //
    // The C Standard Library <stdint.h> header.
    //
    #pragma once
    #define _STDINT
    
    #include <vcruntime.h>
    
    #if _VCRT_COMPILER_PREPROCESSOR
    
    #pragma warning(push)
    #pragma warning(disable: _VCRUNTIME_DISABLED_WARNINGS)
    
    typedef signed char        int8_t;
    typedef short              int16_t;
    typedef int                int32_t;
    typedef long long          int64_t;
    typedef unsigned char      uint8_t;
    typedef unsigned short     uint16_t;
    typedef unsigned int       uint32_t;
    typedef unsigned long long uint64_t;
    
    typedef signed char        int_least8_t;
    typedef short              int_least16_t;
    typedef int                int_least32_t;
    typedef long long          int_least64_t;
    typedef unsigned char      uint_least8_t;
    typedef unsigned short     uint_least16_t;
    typedef unsigned int       uint_least32_t;
    typedef unsigned long long uint_least64_t;
    
    typedef signed char        int_fast8_t;
    typedef int                int_fast16_t;
    typedef int                int_fast32_t;
    typedef long long          int_fast64_t;
    typedef unsigned char      uint_fast8_t;
    typedef unsigned int       uint_fast16_t;
    typedef unsigned int       uint_fast32_t;
    typedef unsigned long long uint_fast64_t;
    
    typedef long long          intmax_t;
    typedef unsigned long long uintmax_t;
    
    // These macros must exactly match those in the Windows SDK's intsafe.h.
    #define INT8_MIN (-127i8 - 1)
    #define INT16_MIN (-32767i16 - 1)
    #define INT32_MIN (-2147483647i32 - 1)
    #define INT64_MIN (-9223372036854775807i64 - 1)
    #define INT8_MAX 127i8
    #define INT16_MAX 32767i16
    #define INT32_MAX 2147483647i32
    #define INT64_MAX 9223372036854775807i64
    #define UINT8_MAX 0xffui8
    #define UINT16_MAX 0xffffui16
    #define UINT32_MAX 0xffffffffui32
    #define UINT64_MAX 0xffffffffffffffffui64
    
    #define INT_LEAST8_MIN INT8_MIN
    #define INT_LEAST16_MIN INT16_MIN
    #define INT_LEAST32_MIN INT32_MIN
    #define INT_LEAST64_MIN INT64_MIN
    #define INT_LEAST8_MAX INT8_MAX
    #define INT_LEAST16_MAX INT16_MAX
    #define INT_LEAST32_MAX INT32_MAX
    #define INT_LEAST64_MAX INT64_MAX
    #define UINT_LEAST8_MAX UINT8_MAX
    #define UINT_LEAST16_MAX UINT16_MAX
    #define UINT_LEAST32_MAX UINT32_MAX
    #define UINT_LEAST64_MAX UINT64_MAX
    
    #define INT_FAST8_MIN INT8_MIN
    #define INT_FAST16_MIN INT32_MIN
    #define INT_FAST32_MIN INT32_MIN
    #define INT_FAST64_MIN INT64_MIN
    #define INT_FAST8_MAX INT8_MAX
    #define INT_FAST16_MAX INT32_MAX
    #define INT_FAST32_MAX INT32_MAX
    #define INT_FAST64_MAX INT64_MAX
    #define UINT_FAST8_MAX UINT8_MAX
    #define UINT_FAST16_MAX UINT32_MAX
    #define UINT_FAST32_MAX UINT32_MAX
    #define UINT_FAST64_MAX UINT64_MAX
    
    #ifdef _WIN64
        #define INTPTR_MIN INT64_MIN
        #define INTPTR_MAX INT64_MAX
        #define UINTPTR_MAX UINT64_MAX
    #else
        #define INTPTR_MIN INT32_MIN
        #define INTPTR_MAX INT32_MAX
        #define UINTPTR_MAX UINT32_MAX
    #endif
    
    #define INTMAX_MIN INT64_MIN
    #define INTMAX_MAX INT64_MAX
    #define UINTMAX_MAX UINT64_MAX
    
    #define PTRDIFF_MIN INTPTR_MIN
    #define PTRDIFF_MAX INTPTR_MAX
    
    #ifndef SIZE_MAX
        // SIZE_MAX definition must match exactly with limits.h for modules support.
        #ifdef _WIN64
            #define SIZE_MAX 0xffffffffffffffffui64
        #else
            #define SIZE_MAX 0xffffffffui32
        #endif
    #endif
    
    #define SIG_ATOMIC_MIN INT32_MIN
    #define SIG_ATOMIC_MAX INT32_MAX
    
    #define WCHAR_MIN 0x0000
    #define WCHAR_MAX 0xffff
    
    #define WINT_MIN 0x0000
    #define WINT_MAX 0xffff
    
    #define INT8_C(x) (x)
    #define INT16_C(x) (x)
    #define INT32_C(x) (x)
    #define INT64_C(x) (x ## LL)
    
    #define UINT8_C(x) (x)
    #define UINT16_C(x) (x)
    #define UINT32_C(x) (x ## U)
    #define UINT64_C(x) (x ## ULL)
    
    #define INTMAX_C(x) INT64_C(x)
    #define UINTMAX_C(x) UINT64_C(x)
    
    #pragma warning(pop) // _VCRUNTIME_DISABLED_WARNINGS
    
    #endif // _VCRT_COMPILER_PREPROCESSOR

## 02. 常量声明 ##

在modbus.h文件中，通过宏定义libmodbus库目前支持的所有Modbus**功能码**

/* Modbus function codes */
    #define MODBUS_FC_READ_COILS 0x01
    #define MODBUS_FC_READ_DISCRETE_INPUTS 0x02
    #define MODBUS_FC_READ_HOLDING_REGISTERS 0x03
    #define MODBUS_FC_READ_INPUT_REGISTERS 0x04
    #define MODBUS_FC_WRITE_SINGLE_COIL 0x05
    #define MODBUS_FC_WRITE_SINGLE_REGISTER 0x06
    #define MODBUS_FC_READ_EXCEPTION_STATUS 0x07
    #define MODBUS_FC_WRITE_MULTIPLE_COILS 0x0F
    #define MODBUS_FC_WRITE_MULTIPLE_REGISTERS 0x10
    #define MODBUS_FC_REPORT_SLAVE_ID 0x11
    #define MODBUS_FC_MASK_WRITE_REGISTER 0x16
    #define MODBUS_FC_WRITE_AND_READ_REGISTERS 0x17

在modbus.h文件中定义了最大可读/可写线圈数量，最大可读/可写寄存器数量。

//广播地址
    #define MODBUS_BROADCAST_ADDRESS 0
    
    /* Modbus_Application_Protocol_V1_1b.pdf (chapter 6 section 1 page 12) * Quantity of Coils to read (2 bytes): 1 to 2000 (0x7D0) * (chapter 6 section 11 page 29) * Quantity of Coils to write (2 bytes): 1 to 1968 (0x7B0) */
    #define MODBUS_MAX_READ_BITS 2000
    #define MODBUS_MAX_WRITE_BITS 1968
    
    /* Modbus_Application_Protocol_V1_1b.pdf (chapter 6 section 3 page 15) * Quantity of Registers to read (2 bytes): 1 to 125 (0x7D) * (chapter 6 section 12 page 31) * Quantity of Registers to write (2 bytes) 1 to 123 (0x7B) * (chapter 6 section 17 page 38) * Quantity of Registers to write in R/W registers (2 bytes) 1 to 121 (0x79) */
    #define MODBUS_MAX_READ_REGISTERS 125
    #define MODBUS_MAX_WRITE_REGISTERS 123
    #define MODBUS_MAX_WR_WRITE_REGISTERS 121
    #define MODBUS_MAX_WR_READ_REGISTERS 125
    
    /* The size of the MODBUS PDU is limited by the size constraint inherited from * the first MODBUS implementation on Serial Line network (max. RS485 ADU = 256 * bytes). Therefore, MODBUS PDU for serial line communication = 256 - Server * address (1 byte) - CRC (2 bytes) = 253 bytes. */
    #define MODBUS_MAX_PDU_LENGTH 253
    
    /* Consequently: * - RTU MODBUS ADU = 253 bytes + Server address (1 byte) + CRC (2 bytes) = 256 * bytes. * - TCP MODBUS ADU = 253 bytes + MBAP (7 bytes) = 260 bytes. * so the maximum of both backend in 260 bytes. This size can used to allocate * an array of bytes to store responses and it will be compatible with the two * backends. */
    #define MODBUS_MAX_ADU_LENGTH 260
    
    /* Random number to avoid errno conflicts */
    #define MODBUS_ENOBASE 112345678

错误码常量

/* Random number to avoid errno conflicts */
    #define MODBUS_ENOBASE 112345678
    
    /* Protocol exceptions */
    enum { 
        MODBUS_EXCEPTION_ILLEGAL_FUNCTION = 0x01,   //非法的功能码
        MODBUS_EXCEPTION_ILLEGAL_DATA_ADDRESS,      //非法的数据地址
        MODBUS_EXCEPTION_ILLEGAL_DATA_VALUE,        //非法的数据值
        MODBUS_EXCEPTION_SLAVE_OR_SERVER_FAILURE,   //从站设备故障
        MODBUS_EXCEPTION_ACKNOWLEDGE,               //ACK异常
        MODBUS_EXCEPTION_SLAVE_OR_SERVER_BUSY,      //从站设备忙
        MODBUS_EXCEPTION_NEGATIVE_ACKNOWLEDGE,      //否定应答
        MODBUS_EXCEPTION_MEMORY_PARITY,             //内存奇偶校验错误
        MODBUS_EXCEPTION_NOT_DEFINED,               //未定义
        MODBUS_EXCEPTION_GATEWAY_PATH,              //网关路径不可用
        MODBUS_EXCEPTION_GATEWAY_TARGET,            //目标设备未能回应
        MODBUS_EXCEPTION_MAX
    };
    
    #define EMBXILFUN (MODBUS_ENOBASE + MODBUS_EXCEPTION_ILLEGAL_FUNCTION)
    #define EMBXILADD (MODBUS_ENOBASE + MODBUS_EXCEPTION_ILLEGAL_DATA_ADDRESS)
    #define EMBXILVAL (MODBUS_ENOBASE + MODBUS_EXCEPTION_ILLEGAL_DATA_VALUE)
    #define EMBXSFAIL (MODBUS_ENOBASE + MODBUS_EXCEPTION_SLAVE_OR_SERVER_FAILURE)
    #define EMBXACK (MODBUS_ENOBASE + MODBUS_EXCEPTION_ACKNOWLEDGE)
    #define EMBXSBUSY (MODBUS_ENOBASE + MODBUS_EXCEPTION_SLAVE_OR_SERVER_BUSY)
    #define EMBXNACK (MODBUS_ENOBASE + MODBUS_EXCEPTION_NEGATIVE_ACKNOWLEDGE)
    #define EMBXMEMPAR (MODBUS_ENOBASE + MODBUS_EXCEPTION_MEMORY_PARITY)
    #define EMBXGPATH (MODBUS_ENOBASE + MODBUS_EXCEPTION_GATEWAY_PATH)
    #define EMBXGTAR (MODBUS_ENOBASE + MODBUS_EXCEPTION_GATEWAY_TARGET)
    
    /* Native libmodbus error codes */
    #define EMBBADCRC (EMBXGTAR + 1) //无效的CRC 
    #define EMBBADDATA (EMBXGTAR + 2) //无效的数据
    #define EMBBADEXC (EMBXGTAR + 3) //无效的异常码
    #define EMBUNKEXC (EMBXGTAR + 4) //保留 未使用
    #define EMBMDATA (EMBXGTAR + 5) //数据过多
    #define EMBBADSLAVE (EMBXGTAR + 6) //响应与查询地址不匹配

## 03. \_modbus结构体声明 ##

在文件modbus-private.h中定义了\_modbus结构体，具体定义如下：

struct _modbus { 
        /* Slave address */
        int slave;      //从站设备地址
        /* Socket or file descriptor */
        int s;  //TCP模式下为套接字 RTU模式下为串口句柄
        int debug;         //是否启用debug模式
        int error_recovery; //错误恢复模式
        struct timeval response_timeout;    //响应超时设置
        struct timeval byte_timeout;        //字节超时设置
        struct timeval indication_timeout;
        //包含一系列通用函数指针
        const modbus_backend_t *backend;
        void *backend_data; //TCP模式下特殊配置数据 RTU模式下特殊配置数据
    };

## 04. modbus\_backend\_t结构体声明 ##

modbus\_backend\_t作为一个重要的结构体，包含了各种处理函数。其定义如下：

typedef struct _modbus_backend { 
        unsigned int backend_type;  //modbus_backend_type_t类型
        unsigned int header_length; //HBMP长度
        unsigned int checksum_length; //错误校验字段长度
        unsigned int max_adu_length; //ADU最大长度
        int (*set_slave) (modbus_t *ctx, int slave); //设置从站设备地址
        //构造查询报文的基本通信帧
        int (*build_request_basis) (modbus_t *ctx, int function, int addr,
                                    int nb, uint8_t *req);
        //构造响应报文的基本通信帧
        int (*build_response_basis) (sft_t *sft, uint8_t *rsp);
        //构造响应报文TID参数
        int (*prepare_response_tid) (const uint8_t *req, int *req_length);
        //发送报文前的预处理
        int (*send_msg_pre) (uint8_t *req, int req_length);
        //发送报文
        ssize_t (*send) (modbus_t *ctx, const uint8_t *req, int req_length);
        //接收报文
        int (*receive) (modbus_t *ctx, uint8_t *req);
        //接收报文 该函数被receive函数调用
        ssize_t (*recv) (modbus_t *ctx, uint8_t *rsp, int rsp_length);
        //用于数据完整性检查
        int (*check_integrity) (modbus_t *ctx, uint8_t *msg,
                                const int msg_length);
        //确认响应报文的帧头是否一致
        int (*pre_check_confirmation) (modbus_t *ctx, const uint8_t *req,
                                       const uint8_t *rsp, int rsp_length);
        //建立连接
        int (*connect) (modbus_t *ctx);
        //关闭连接
        void (*close) (modbus_t *ctx);
        //清空缓冲区
        int (*flush) (modbus_t *ctx);
        //用于设置超时并读取通信事件，以检测是否存在待接收数据
        int (*select) (modbus_t *ctx, fd_set *rset, struct timeval *tv, int msg_length);
        //释放内存
        void (*free) (modbus_t *ctx);
    } modbus_backend_t;

## 05. modbus\_mapping\_t结构体声明 ##

modbus\_mapping\_t声明在modbus.h文件中，其声明如下：

typedef struct _modbus modbus_t;
    
    typedef struct _modbus_mapping_t { 
        int nb_bits;                    //线圈寄存器的数量
        int start_bits;                 //线圈寄存器的起始地址
        int nb_input_bits;              //离散输入寄存器的数量 
        int start_input_bits;           //离散输入寄存器的起始地址
        int nb_input_registers;         //输入寄存器的数量
        int start_input_registers;      //输入寄存器的起始地址
        int nb_registers;               //保持寄存器的数量
        int start_registers;            //保持寄存器的起始地址
        uint8_t *tab_bits;              //指向线圈寄存器的值
        uint8_t *tab_input_bits;        //指向离散输入寄存器的值
        uint16_t *tab_input_registers;  //指向输入寄存器的值
    
        uint16_t *tab_registers;        //指向保持寄存器的值
    } modbus_mapping_t;

## 06. 附录 ##

libmodbus源码下载：[https://github.com/stephane/libmodbus][https_github.com_stephane_libmodbus]

[https_github.com_stephane_libmodbus]: https://github.com/stephane/libmodbus