判断linux 串口发送完成

#include <sys/select.h>
#include <fcntl.h>
#include <unistd.h>

int main() {
    int fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY);
    if (fd == -1) {
        perror("open_port: Unable to open /dev/ttyS0");
        return -1;
    }

    fd_set writefds;
    FD_ZERO(&writefds);
    FD_SET(fd, &writefds);

    struct timeval timeout;
    timeout.tv_sec = 5;
    timeout.tv_usec = 0;

    int ret = select(fd + 1, NULL, &writefds, NULL, &timeout);
    if (ret == -1) {
        perror("select");
    } else if (ret) {
        if (FD_ISSET(fd, &writefds)) {
            // 串口可写，可以发送数据
        }
    }

    close(fd);
    return 0;
}

#include <termios.h>
#include <fcntl.h>
#include <unistd.h>

int main() {
    int fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY);
    if (fd == -1) {
        perror("open_port: Unable to open /dev/ttyS0");
        return -1;
    }

    // 设置串口参数...

    write(fd, "Hello, World!", 13);
    tcdrain(fd); // 等待所有数据发送完成

    close(fd);
    return 0;
}