libmodbus的編譯和使用

libmodbus 是支持Linux，Mac OS X，QNX和win32 的一個modbus庫，支持modbus TCP和RTU 兩種模式。

libmodbus 的官網：https://www.libmodbus.org/

當前版本爲：v3.1.6

 編譯

我在win10 下的wsl 下編譯的，相信在ubuntu linux 下也大同小異。

   下載解壓 libmodbus 的源碼，F:lib modbus-3.1.6文件夾中。

    進入wsl 的console，輸入下述命令完成編譯

  cd /mnt/f/libmodbus-3.1.6

  ./configure

  make

  libmodbus 包中包含了tests 目錄，其中有一些測試程序，已經同時被編譯。

 運行測試程序

   ./bandwidth_server_one

另外開啓一個wsl console 窗口

 輸入 ./bandwidth_client

 可以看到輸出信息

  bandwidth_client /bandwidth_server是用來測試modbus TCP 速率的測試程序。相對比較簡單。下面列出了bandwidth_client 的程序源碼

/*
 * Copyright © 2008-2014 Stéphane Raimbault <[email protected]>
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <stdio.h>
#ifndef _MSC_VER
#include <unistd.h>
#include <sys/time.h>
#endif
#include <string.h>
#include <stdlib.h>
#include <time.h>
#include <errno.h>

#include <modbus.h>

#define G_MSEC_PER_SEC 1000

static uint32_t gettime_ms(void)
{
    struct timeval tv;
#if !defined(_MSC_VER)
    gettimeofday(&tv, NULL);
    return (uint32_t) tv.tv_sec * 1000 + tv.tv_usec / 1000;
#else
    return GetTickCount();
#endif
}

enum {
    TCP,
    RTU
};

/* Tests based on PI-MBUS-300 documentation */
int main(int argc, char *argv[])
{
    uint8_t *tab_bit;
    uint16_t *tab_reg;
    modbus_t *ctx;
    int i;
    int nb_points;
    double elapsed;
    uint32_t start;
    uint32_t end;
    uint32_t bytes;
    uint32_t rate;
    int rc;
    int n_loop;
    int use_backend;

    if (argc > 1) {
        if (strcmp(argv[1], "tcp") == 0) {
            use_backend = TCP;
            n_loop = 100000;
        } else if (strcmp(argv[1], "rtu") == 0) {
            use_backend = RTU;
            n_loop = 100;
        } else {
            printf("Usage:\n  %s [tcp|rtu] - Modbus client to measure data bandwith\n\n", argv[0]);
            exit(1);
        }
    } else {
        /* By default */
        use_backend = TCP;
        n_loop = 100000;
    }

    if (use_backend == TCP) {
        ctx = modbus_new_tcp("127.0.0.1", 1502);
    } else {
        ctx = modbus_new_rtu("/dev/ttyUSB1", 115200, 'N', 8, 1);
        modbus_set_slave(ctx, 1);
    }
    if (modbus_connect(ctx) == -1) {
        fprintf(stderr, "Connection failed: %s\n",
                modbus_strerror(errno));
        modbus_free(ctx);
        return -1;
    }

    /* Allocate and initialize the memory to store the status */
    tab_bit = (uint8_t *) malloc(MODBUS_MAX_READ_BITS * sizeof(uint8_t));
    memset(tab_bit, 0, MODBUS_MAX_READ_BITS * sizeof(uint8_t));

    /* Allocate and initialize the memory to store the registers */
    tab_reg = (uint16_t *) malloc(MODBUS_MAX_READ_REGISTERS * sizeof(uint16_t));
    memset(tab_reg, 0, MODBUS_MAX_READ_REGISTERS * sizeof(uint16_t));

    printf("READ BITS\n\n");

    nb_points = MODBUS_MAX_READ_BITS;
    start = gettime_ms();
    for (i=0; i<n_loop; i++) {
        rc = modbus_read_bits(ctx, 0, nb_points, tab_bit);
        if (rc == -1) {
            fprintf(stderr, "%s\n", modbus_strerror(errno));
            return -1;
        }
    }
    end = gettime_ms();
    elapsed = end - start;

    rate = (n_loop * nb_points) * G_MSEC_PER_SEC / (end - start);
    printf("Transfert rate in points/seconds:\n");
    printf("* %d points/s\n", rate);
    printf("\n");

    bytes = n_loop * (nb_points / 8) + ((nb_points % 8) ? 1 : 0);
    rate = bytes / 1024 * G_MSEC_PER_SEC / (end - start);
    printf("Values:\n");
    printf("* %d x %d values\n", n_loop, nb_points);
    printf("* %.3f ms for %d bytes\n", elapsed, bytes);
    printf("* %d KiB/s\n", rate);
    printf("\n");

    /* TCP: Query and reponse header and values */
    bytes = 12 + 9 + (nb_points / 8) + ((nb_points % 8) ? 1 : 0);
    printf("Values and TCP Modbus overhead:\n");
    printf("* %d x %d bytes\n", n_loop, bytes);
    bytes = n_loop * bytes;
    rate = bytes / 1024 * G_MSEC_PER_SEC / (end - start);
    printf("* %.3f ms for %d bytes\n", elapsed, bytes);
    printf("* %d KiB/s\n", rate);
    printf("\n\n");

    printf("READ REGISTERS\n\n");

    nb_points = MODBUS_MAX_READ_REGISTERS;
    start = gettime_ms();
    for (i=0; i<n_loop; i++) {
        rc = modbus_read_registers(ctx, 0, nb_points, tab_reg);
        if (rc == -1) {
            fprintf(stderr, "%s\n", modbus_strerror(errno));
            return -1;
        }
    }
    end = gettime_ms();
    elapsed = end - start;

    rate = (n_loop * nb_points) * G_MSEC_PER_SEC / (end - start);
    printf("Transfert rate in points/seconds:\n");
    printf("* %d registers/s\n", rate);
    printf("\n");

    bytes = n_loop * nb_points * sizeof(uint16_t);
    rate = bytes / 1024 * G_MSEC_PER_SEC / (end - start);
    printf("Values:\n");
    printf("* %d x %d values\n", n_loop, nb_points);
    printf("* %.3f ms for %d bytes\n", elapsed, bytes);
    printf("* %d KiB/s\n", rate);
    printf("\n");

    /* TCP:Query and reponse header and values */
    bytes = 12 + 9 + (nb_points * sizeof(uint16_t));
    printf("Values and TCP Modbus overhead:\n");
    printf("* %d x %d bytes\n", n_loop, bytes);
    bytes = n_loop * bytes;
    rate = bytes / 1024 * G_MSEC_PER_SEC / (end - start);
    printf("* %.3f ms for %d bytes\n", elapsed, bytes);
    printf("* %d KiB/s\n", rate);
    printf("\n\n");

    printf("WRITE AND READ REGISTERS\n\n");

    nb_points = MODBUS_MAX_WR_WRITE_REGISTERS;
    start = gettime_ms();
    for (i=0; i<n_loop; i++) {
        rc = modbus_write_and_read_registers(ctx,
                                             0, nb_points, tab_reg,
                                             0, nb_points, tab_reg);
        if (rc == -1) {
            fprintf(stderr, "%s\n", modbus_strerror(errno));
            return -1;
        }
    }
    end = gettime_ms();
    elapsed = end - start;

    rate = (n_loop * nb_points) * G_MSEC_PER_SEC / (end - start);
    printf("Transfert rate in points/seconds:\n");
    printf("* %d registers/s\n", rate);
    printf("\n");

    bytes = n_loop * nb_points * sizeof(uint16_t);
    rate = bytes / 1024 * G_MSEC_PER_SEC / (end - start);
    printf("Values:\n");
    printf("* %d x %d values\n", n_loop, nb_points);
    printf("* %.3f ms for %d bytes\n", elapsed, bytes);
    printf("* %d KiB/s\n", rate);
    printf("\n");

    /* TCP:Query and reponse header and values */
    bytes = 12 + 9 + (nb_points * sizeof(uint16_t));
    printf("Values and TCP Modbus overhead:\n");
    printf("* %d x %d bytes\n", n_loop, bytes);
    bytes = n_loop * bytes;
    rate = bytes / 1024 * G_MSEC_PER_SEC / (end - start);
    printf("* %.3f ms for %d bytes\n", elapsed, bytes);
    printf("* %d KiB/s\n", rate);
    printf("\n");

    /* Free the memory */
    free(tab_bit);
    free(tab_reg);

    /* Close the connection */
    modbus_close(ctx);
    modbus_free(ctx);

    return 0;
}

上面的例子測試讀10萬個點，讀10萬個寄存器，讀寫十萬次的時間。

主要用法

上下文類型context

前面已經提到，libmodbus 支持TCP和RTU 兩種通信方式，前一種是支持TCP/IP 協議的，而RTU 是支持RS485 串口的協議。libmodbus 庫的設計將TCP/RTU 模式的實現細節在用戶端屏蔽掉了。modbus 的類型數據放置在一個結構類型中，當新建一個modbus 接口時，填入有關的參數，並將這個包含接口參數的結構指針返回給用戶，這個指針稱爲上下文類型。

例如：

 在以後的各種操作中，用戶只要帶有contex 參數就可以了，不再關心是modbus TCP 還是modbus RTU 。這兩種模式的各種函數都是一樣的。

modbus_t *ctx;

 

ctx = modbus_new_tcp("127.0.0.1", 1502);

if (ctx == NULL) {

    fprintf(stderr, "Unable to allocate libmodbus context\n");

    return -1;

}

 

if (modbus_connect(ctx) == -1) {

    fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));

    modbus_free(ctx);

    return -1;

}

顯然，這是一種優雅的程序設計方式。

讀比特位

rc = modbus_write_bit(ctx, addr, tab_rq_bits[0]);

 

寫比特位

rc = modbus_read_bits(ctx, addr, 1, tab_rp_bits);

讀寄存器

int modbus_read_registers(modbus_t *ctx, int addr, int nb, uint16_t *dest);

寫寄存器

int modbus_write_register(modbus_t *ctx, int addr, const uint16_t value);

讀寫寄存器

int modbus_write_and_read_registers(modbus_t *ctx, int write_addr, int write_nb, const uint16_t *src, int read_addr, int read_nb, const uint16_t *dest);