modbus 处理粘包 C代码

以下是一个处理Modbus粘包的C代码示例：

#define MAX_BUF_SIZE 256
#define MODBUS_HEADER_SIZE 6

int read_data(int fd, char *buf, int buf_size) {
    int bytes_read = 0;
    int total_bytes_read = 0;
    int bytes_to_read = buf_size;
    while (total_bytes_read < buf_size) {
        bytes_read = read(fd, buf + total_bytes_read, bytes_to_read);
        if (bytes_read < 0) {
            perror("read");
            return -1;
        } else if (bytes_read == 0) {
            break;
        } else {
            total_bytes_read += bytes_read;
            bytes_to_read -= bytes_read;
        }
    }
    return total_bytes_read;
}

int handle_modbus_packet(int fd, char *buf, int buf_size) {
    int bytes_read = 0;
    int total_bytes_read = 0;
    int bytes_to_read = buf_size;
    while (total_bytes_read < buf_size) {
        bytes_read = read_data(fd, buf + total_bytes_read, bytes_to_read);
        if (bytes_read < 0) {
            return -1;
        } else if (bytes_read == 0) {
            break;
        } else {
            total_bytes_read += bytes_read;
            bytes_to_read -= bytes_read;
            if (total_bytes_read >= MODBUS_HEADER_SIZE) {
                int packet_size = buf[4] << 8 | buf[5];
                if (total_bytes_read >= packet_size + MODBUS_HEADER_SIZE) {
                    // handle packet
                    // ...
                    // move remaining data to the beginning of the buffer
                    int remaining_bytes = total_bytes_read - packet_size - MODBUS_HEADER_SIZE;
                    if (remaining_bytes > 0) {
                        memmove(buf, buf + packet_size + MODBUS_HEADER_SIZE, remaining_bytes);
                    }
                    total_bytes_read = remaining_bytes;
                }
            }
        }
    }
    return total_bytes_read;
}

int main(int argc, char *argv[]) {
    char buf[MAX_BUF_SIZE];
    int fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd < 0) {
        perror("open");
        return -1;
    }
    struct termios options;
    tcgetattr(fd, &options);
    cfsetispeed(&options, B9600);
    cfsetospeed(&options, B9600);
    options.c_cflag |= (CLOCAL | CREAD);
    options.c_cflag &= ~PARENB;
    options.c_cflag &= ~CSTOPB;
    options.c_cflag &= ~CSIZE;
    options.c_cflag |= CS8;
    options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
    options.c_oflag &= ~OPOST;
    tcsetattr(fd, TCSANOW, &options);
    fcntl(fd, F_SETFL, 0);
    while (1) {
        int bytes_read = handle_modbus_packet(fd, buf, MAX_BUF_SIZE);
        if (bytes_read < 0) {
            break;
        }
    }
    close(fd);
    return 0;
}

在上面的代码示例中，`handle_modbus_packet`函数用于处理Modbus数据包。它从串口读取数据，并检查数据是否已经足够形成一个完整的数据包。如果是，则处理该数据包，然后将剩余的数据移动到缓冲区的开头。如果不是，则继续等待更多数据。`read_data`函数用于从串口读取指定数量的数据。在主函数中，该代码示例无限循环调用`handle_modbus_packet`函数以处理来自串口的数据。