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一、源碼下載

libmodbus官網是libmodbus，首頁就是個很霸氣的標語，我必須copy過來“The most popular Open Source library to communicate with Modbus devices.”

點擊紅色標識處進入下載頁面：

最新版的是v3.1.10，把gz源碼文件下載下來。

二、源碼編譯

將下載的libmodbus-3.1.10.tar.gz源碼傳輸到X86 PC編譯環境（具體環境搭建在上文已經介紹），解壓源碼，可以順便看看相關文件樹：

root@EliteDesk800:~$ tar -xzvf libmodbus-3.1.10.tar.gz
libmodbus-3.1.10/configure.ac
libmodbus-3.1.10/libmodbus.pc.in
libmodbus-3.1.10/configure
libmodbus-3.1.10/AUTHORS
libmodbus-3.1.10/tests/
libmodbus-3.1.10/config.h.in
libmodbus-3.1.10/COPYING.LESSER
libmodbus-3.1.10/Makefile.am
libmodbus-3.1.10/README.md
libmodbus-3.1.10/NEWS
libmodbus-3.1.10/m4/
libmodbus-3.1.10/Makefile.in
libmodbus-3.1.10/aclocal.m4
libmodbus-3.1.10/src/
libmodbus-3.1.10/src/modbus-private.h
libmodbus-3.1.10/src/modbus-data.c
libmodbus-3.1.10/src/modbus.c
libmodbus-3.1.10/src/modbus-tcp.c
libmodbus-3.1.10/src/modbus-rtu.h
libmodbus-3.1.10/src/modbus-version.h
libmodbus-3.1.10/src/Makefile.am
libmodbus-3.1.10/src/modbus-version.h.in
libmodbus-3.1.10/src/modbus-rtu.c
libmodbus-3.1.10/src/modbus-tcp.h
libmodbus-3.1.10/src/win32/
libmodbus-3.1.10/src/modbus.h
libmodbus-3.1.10/src/modbus-tcp-private.h
libmodbus-3.1.10/src/Makefile.in
libmodbus-3.1.10/src/modbus-rtu-private.h
libmodbus-3.1.10/src/win32/modbus.dll.manifest.in
libmodbus-3.1.10/m4/ltversion.m4
libmodbus-3.1.10/m4/libtool.m4
libmodbus-3.1.10/m4/ltoptions.m4
libmodbus-3.1.10/m4/ltsugar.m4
libmodbus-3.1.10/m4/lt~obsolete.m4
libmodbus-3.1.10/tests/random-test-client.c
libmodbus-3.1.10/tests/LICENSE
libmodbus-3.1.10/tests/bandwidth-server-one.c
libmodbus-3.1.10/tests/unit-test.h
libmodbus-3.1.10/tests/unit-test-client.c
libmodbus-3.1.10/tests/bandwidth-server-many-up.c
libmodbus-3.1.10/tests/Makefile.am
libmodbus-3.1.10/tests/README.md
libmodbus-3.1.10/tests/unit-test-server.c
libmodbus-3.1.10/tests/unit-tests.sh
libmodbus-3.1.10/tests/version.c
libmodbus-3.1.10/tests/bandwidth-client.c
libmodbus-3.1.10/tests/Makefile.in
libmodbus-3.1.10/tests/random-test-server.c
libmodbus-3.1.10/build-aux/install-sh
libmodbus-3.1.10/build-aux/ltmain.sh
libmodbus-3.1.10/build-aux/config.guess
libmodbus-3.1.10/build-aux/depcomp
libmodbus-3.1.10/build-aux/missing
libmodbus-3.1.10/build-aux/config.sub
libmodbus-3.1.10/build-aux/compile
libmodbus-3.1.10/build-aux/test-driver

進入libmodbus-3.1.10文件夾執行 makedir -p install創建install目錄。
然后執行./configure ac_cv_func_malloc_0_nonnull=yes --host=arm-linux-gnueabi --enable-static --prefix=$(pwd)/install/ 進行配置，host選擇arm-linux-gnueabi適合T113的Cortex-A7內核。
配置執行完畢后顯示如下：

后面也沒啥，直接make & make install即可。

root@EliteDesk800:~/libmodbus-3.1.10$ make
make --no-print-directory all-recursive
Making all in src
  CC       modbus.lo
  CC       modbus-data.lo
  CC       modbus-rtu.lo
  CC       modbus-tcp.lo
  CCLD     libmodbus.la
Making all in tests
make  all-am
  CC       bandwidth-server-one.o
  CCLD     bandwidth-server-one
  CC       bandwidth-server-many-up.o
  CCLD     bandwidth-server-many-up
  CC       bandwidth-client.o
  CCLD     bandwidth-client
  CC       random-test-server.o
  CCLD     random-test-server
  CC       random-test-client.o
  CCLD     random-test-client
  CC       unit-test-server.o
  CCLD     unit-test-server
  CC       unit-test-client.o
  CCLD     unit-test-client
  CC       version.o
  CCLD     version
root@EliteDesk800:~/libmodbus-3.1.10$ make install

最后生成lib都在，具體如下：

root@EliteDesk800:~/libmodbus-3.1.10$ file install/lib/
libmodbus.a         libmodbus.la        libmodbus.so        libmodbus.so.5      libmodbus.so.5.1.0  pkgconfig/

看看文件，“ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV)”文件沒錯：

root@EliteDesk800:~/libmodbus-3.1.10$ file install/lib/libmodbus.*
install/lib/libmodbus.a:        current ar archive
install/lib/libmodbus.la:       libtool library file, ASCII text
install/lib/libmodbus.so:       symbolic link to libmodbus.so.5.1.0
install/lib/libmodbus.so.5:     symbolic link to libmodbus.so.5.1.0
install/lib/libmodbus.so.5.1.0: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, BuildID[sha1]=34c254066cb77dc6565cc41963f872b90e5dbefc, with debug_info, not stripped

然后把所有的libmodbus文件拷貝到米爾-全志T113-i開發板的/lib目錄下。

三、測試

libmodbus.so已經編成，接下來就是測試是否能正常工作。

（一）選擇串口

MYC-YT113i 核心板處理器擁有高達 6 路串口。由于芯片的管腳復用關系，默認配置了 2 路串口，UART4 和 UART5。

可以從米爾-全志T113-i開發板的系統設備上印證。

那就直接選擇UART4吧，找到UART4的針腳即可。在米爾-全志T113-i開發板的硬件手冊中找到。

紅框處的3個pin，反咋GND也要接。

具體連接如圖。

（二）測試demo

具體代碼如下，在X86 PC上編譯好，SCP到米爾-全志T113-i開發板。

#include 
#include 
#include 
#include 
#include 
#include 

// clang-format off
#ifdef _WIN32
# include 
#else
# include 
#endif

/* For MinGW */
#ifndef MSG_NOSIGNAL
# define MSG_NOSIGNAL 0
#endif
// clang-format on

#include "unit-test.h"

enum {
    TCP,
    TCP_PI,
    RTU
};

int main(int argc, char *argv[])
{
    int s = -1;
    modbus_t *ctx;
    modbus_mapping_t *mb_mapping;
    int rc;
    int i;
    int use_backend;
    uint8_t *query;
    int header_length;
    char *ip_or_device;

    if (argc > 1) {
        if (strcmp(argv[1], "tcp") == 0) {
            use_backend = TCP;
        } else if (strcmp(argv[1], "tcppi") == 0) {
            use_backend = TCP_PI;
        } else if (strcmp(argv[1], "rtu") == 0) {
            use_backend = RTU;
        } else {
            printf("Modbus server for unit testing.n");
            printf("Usage:n  %s [tcp|tcppi|rtu] []n", argv[0]);
            printf("Eg. tcp 127.0.0.1 or rtu /dev/ttyUSB0nn");
            return -1;
        }
    } else {
        /* By default */
        use_backend = TCP;
    }

    if (argc > 2) {
        ip_or_device = argv[2];
    } else {
        switch (use_backend) {
        case TCP:
            ip_or_device = "127.0.0.1";
            break;
        case TCP_PI:
            ip_or_device = "::1";
            break;
        case RTU:
            ip_or_device = "/dev/ttyUSB0";
            break;
        default:
            break;
        }
    }

    if (use_backend == TCP) {
        ctx = modbus_new_tcp(ip_or_device, 1502);
        query = malloc(MODBUS_TCP_MAX_ADU_LENGTH);
    } else if (use_backend == TCP_PI) {
        ctx = modbus_new_tcp_pi(ip_or_device, "1502");
        query = malloc(MODBUS_TCP_MAX_ADU_LENGTH);
    } else {
        ctx = modbus_new_rtu(ip_or_device, 115200, 'N', 8, 1);
        modbus_set_slave(ctx, SERVER_ID);
        query = malloc(MODBUS_RTU_MAX_ADU_LENGTH);
    }

    header_length = modbus_get_header_length(ctx);

    modbus_set_debug(ctx, TRUE);

    mb_mapping = modbus_mapping_new_start_address(UT_BITS_ADDRESS,
                                                  UT_BITS_NB,
                                                  UT_INPUT_BITS_ADDRESS,
                                                  UT_INPUT_BITS_NB,
                                                  UT_REGISTERS_ADDRESS,
                                                  UT_REGISTERS_NB_MAX,
                                                  UT_INPUT_REGISTERS_ADDRESS,
                                                  UT_INPUT_REGISTERS_NB);
    if (mb_mapping == NULL) {
        fprintf(stderr, "Failed to allocate the mapping: %sn", modbus_strerror(errno));
        modbus_free(ctx);
        return -1;
    }

    /* Examples from PI_MODBUS_300.pdf.
       Only the read-only input values are assigned. */

    /* Initialize input values that's can be only done server side. */
    modbus_set_bits_from_bytes(
        mb_mapping->tab_input_bits, 0, UT_INPUT_BITS_NB, UT_INPUT_BITS_TAB);

    /* Initialize values of INPUT REGISTERS */
    for (i = 0; i < UT_INPUT_REGISTERS_NB; i++) {
        mb_mapping-?>tab_input_registers[i] = UT_INPUT_REGISTERS_TAB[i];
    }

    if (use_backend == TCP) {
        s = modbus_tcp_listen(ctx, 1);
        modbus_tcp_accept(ctx, &s);
    } else if (use_backend == TCP_PI) {
        s = modbus_tcp_pi_listen(ctx, 1);
        modbus_tcp_pi_accept(ctx, &s);
    } else {
        rc = modbus_connect(ctx);
        if (rc == -1) {
            fprintf(stderr, "Unable to connect %sn", modbus_strerror(errno));
            modbus_free(ctx);
            return -1;
        }
    }

    for (;;) {
        do {
            rc = modbus_receive(ctx, query);
            /* Filtered queries return 0 */
        } while (rc == 0);

        /* The connection is not closed on errors which require on reply such as
           bad CRC in RTU. */
        if (rc == -1 && errno != EMBBADCRC) {
            /* Quit */
            break;
        }

        /* Special server behavior to test client */
        if (query[header_length] == 0x03) {
            /* Read holding registers */

            if (MODBUS_GET_INT16_FROM_INT8(query, header_length + 3) ==
                UT_REGISTERS_NB_SPECIAL) {
                printf("Set an incorrect number of valuesn");
                MODBUS_SET_INT16_TO_INT8(
                    query, header_length + 3, UT_REGISTERS_NB_SPECIAL - 1);
            } else if (MODBUS_GET_INT16_FROM_INT8(query, header_length + 1) ==
                       UT_REGISTERS_ADDRESS_SPECIAL) {
                printf("Reply to this special register address by an exceptionn");
                modbus_reply_exception(ctx, query, MODBUS_EXCEPTION_SLAVE_OR_SERVER_BUSY);
                continue;
            } else if (MODBUS_GET_INT16_FROM_INT8(query, header_length + 1) ==
                       UT_REGISTERS_ADDRESS_INVALID_TID_OR_SLAVE) {
                const int RAW_REQ_LENGTH = 5;
                uint8_t raw_req[] = {(use_backend == RTU) ? INVALID_SERVER_ID : 0xFF,
                                     0x03,
                                     0x02,
                                     0x00,
                                     0x00};

                printf("Reply with an invalid TID or slaven");
                modbus_send_raw_request(ctx, raw_req, RAW_REQ_LENGTH * sizeof(uint8_t));
                continue;
            } else if (MODBUS_GET_INT16_FROM_INT8(query, header_length + 1) ==
                       UT_REGISTERS_ADDRESS_SLEEP_500_MS) {
                printf("Sleep 0.5 s before replyingn");
                usleep(500000);
            } else if (MODBUS_GET_INT16_FROM_INT8(query, header_length + 1) ==
                       UT_REGISTERS_ADDRESS_BYTE_SLEEP_5_MS) {
                /* Test low level only available in TCP mode */
                /* Catch the reply and send reply byte a byte */
                uint8_t req[] = "x00x1Cx00x00x00x05xFFx03x02x00x00";
                int req_length = 11;
                int w_s = modbus_get_socket(ctx);
                if (w_s == -1) {
                    fprintf(stderr, "Unable to get a valid socket in special testn");
                    continue;
                }

                /* Copy TID */
                req[1] = query[1];
                for (i = 0; i < req_length; i++) {
                    printf("(%.2X)", req[i]);
                    usleep(5000);
                    rc = send(w_s, (const char *) (req + i), 1, MSG_NOSIGNAL);
                    if (rc == -1) {
                        break;
                    }
                }
                continue;
            }
        }

        rc = modbus_reply(ctx, query, rc, mb_mapping);
        if (rc == -1) {
            break;
        }
    }

    printf("Quit the loop: %sn", modbus_strerror(errno));

    if (use_backend == TCP) {
        if (s != -1) {
            close(s);
        }
    }
    modbus_mapping_free(mb_mapping);
    free(query);
    /* For RTU */
    modbus_close(ctx);
    modbus_free(ctx);

    return 0;
}

（三）運行

UART4接USB-TTL模塊連PC，然后PC運行modbus-pull。

在米爾-全志T113-i開發板上打開測試程序。

root@myd-yt113-i:~# ./mod-server rtu /dev/ttyAS4
Opening /dev/ttyAS4 at 115200 bauds (N, 8, 1)
Waiting for an indication...

modbus-pull讀寄存器，設備id是demo里面寫死的。

米爾-全志T113-i開發板側的log顯示已經收到modbus信息，不支持00地址的read，不管了，反正只測試libmodbus是否移植成功，業務上的錯誤先不管：

Waiting for an indication...

Illegal data address 0x0 in read_registers
[11][83][02][C1][34]
Waiting for an indication...

Illegal data address 0x0 in read_registers
[11][83][02][C1][34]
Waiting for an indication...

Illegal data address 0x0 in read_registers
[11][83][02][C1][34]
Waiting for an indication...

Illegal data address 0x0 in read_registers
[11][83][02][C1][34]
Waiting for an indication...

Illegal data address 0x0 in read_registers
[11][83][02][C1][34]