Linux下利用select实现串口数据读取过程

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <termios.h>
#include <unistd.h>
#include <sys/select.h>

// 设置串口波特率
void SetSpeed(int fd, int speed) {
    struct termios options;
    tcgetattr(fd, &options);
    switch (speed) {
        case 115200:
            cfsetispeed(&options, B115200);
            cfsetospeed(&options, B115200);
            break;
        // 可以添加更多波特率设置
        default:
            cfsetispeed(&options, B115200);
            cfsetospeed(&options, B115200);
            break;
    }
    tcsetattr(fd, TCSANOW, &options);
}

// 设置串口参数
void SetParity(int fd, int databits, int stopbits, char parity) {
    struct termios options;
    tcgetattr(fd, &options);

    // 设置数据位
    options.c_cflag &= ~CSIZE;
    switch (databits) {
        case 7:
            options.c_cflag |= CS7;
            break;
        case 8:
            options.c_cflag |= CS8;
            break;
        default:
            options.c_cflag |= CS8;
            break;
    }

    // 设置奇偶校验位
    switch (parity) {
        case 'n':
        case 'N':
            options.c_cflag &= ~PARENB;
            options.c_cflag &= ~PARODD;
            break;
        case 'o':
        case 'O':
            options.c_cflag |= (PARODD | PARENB);
            break;
        case 'e':
        case 'E':
            options.c_cflag |= PARENB;
            options.c_cflag &= ~PARODD;
            break;
        default:
            options.c_cflag &= ~PARENB;
            options.c_cflag &= ~PARODD;
            break;
    }

    // 设置停止位
    switch (stopbits) {
        case 1:
            options.c_cflag &= ~CSTOPB;
            break;
        case 2:
            options.c_cflag |= CSTOPB;
            break;
        default:
            options.c_cflag &= ~CSTOPB;
            break;
    }

    tcsetattr(fd, TCSANOW, &options);
}

int main(void) {
    int fd;
    unsigned char buf[300];
    unsigned short len;
    fd = open("/dev/ttyS1", O_RDWR);
    if (fd == -1) {
        perror("can't open serial\n");
        return -1;
    }

    SetParity(fd, 8, 1, 'n');
    SetSpeed(fd, 115200);

    fd_set readfds;
    struct timeval timeout;

    while (1) {
        // 清空文件描述符集
        FD_ZERO(&readfds);
        // 将串口文件描述符加入读文件描述符集
        FD_SET(fd, &readfds);

        // 设置超时时间
        timeout.tv_sec = 0;
        timeout.tv_usec = 20000;

        // 调用 select 函数等待事件发生
        int activity = select(fd + 1, &readfds, NULL, NULL, &timeout);

        if (activity < 0) {
            perror("select error");
            break;
        } else if (activity > 0) {
            // 检查是否是串口文件描述符有数据可读
            if (FD_ISSET(fd, &readfds)) {
                len = read(fd, buf, 100);
                if (len > 0) {
                    write(fd, buf, len);
                }
            }
        }
    }

    close(fd);
    return 0;
}