Question

简单的问题。当我写入/dev/ttyS1时，它不会立即刷新它。这可能与我的串口初始化有关...但我无法弄明白！我的代码是这样的：

#define BAUDRATE B115200
#define MODEMDEVICE "/dev/ttyS1"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1

volatile int STOP = FALSE;

void signal_handler_IO(int status); /* definition of signal handler */
int wait_flag = TRUE; /* TRUE while no signal received */


int main()
{
    int fd, c, res;
    struct termios oldtio, newtio;
    struct sigaction saio; /* definition of signal action */
    char buf[255];

    /* open the device to be non-blocking (read will return immediatly) */
    fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NONBLOCK);
    if (fd < 0) {
        perror(MODEMDEVICE);
        exit(-1);
    }

    /* install the signal handler before making the device asynchronous */
    saio.sa_handler = signal_handler_IO;
    //saio.sa_mask = 0;
    saio.sa_flags = 0;
    saio.sa_restorer = NULL;
    sigaction(SIGIO, &saio, NULL);

    /* allow the process to receive SIGIO */
    fcntl(fd, F_SETOWN, getpid());
    /* Make the file descriptor asynchronous (the manual page says only
     O_APPEND and O_NONBLOCK, will work with F_SETFL...) */
    fcntl(fd, F_SETFL, FASYNC);

    tcgetattr(fd, &oldtio); /* save current port settings */
    /* set new port settings for canonical input processing */
    newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
    newtio.c_iflag = IGNPAR | ICRNL;
    newtio.c_oflag = 0;
    newtio.c_lflag = ICANON;
    newtio.c_cc[VMIN] = 1;
    newtio.c_cc[VTIME] = 0;
    tcflush(fd, TCIFLUSH);
    tcsetattr(fd, TCSANOW, &newtio);

    int i = 0;

    /* loop while waiting for input. normally we would do something
     useful here */
    while (1) {
        printf(".\n");
        usleep(100000);
        //tcflush(fd, TCOFLUSH);
        //tcflush(fd, TCIOFLUSH);
        i++;
        if (i == 20) {
            // ------------------ write to serial ----------------------
            int n = write(fd, "ATZ\n", 4);
            if (n < 0)
                fputs("write() of 4 bytes failed!\n", stderr);

        }

        /* after receiving SIGIO, wait_flag = FALSE, input is available
         and can be read */
        if (wait_flag == FALSE ) {
            res = read(fd, buf, 255);
            buf[res] = 0;
            printf(":%s:%d\n", buf, res);
            wait_flag = TRUE; /* wait for new input */
        }
    }
    /* restore old port settings */
    tcsetattr(fd, TCSANOW, &oldtio);
}



void signal_handler_IO(int status) {
    printf("received SIGIO signal.\n");
    wait_flag = FALSE;
}

有什么想法吗？

Answer 1

您已通过设置CRTSCTS启用了CTS硬件流控制。这意味着如果UART的CTS输入未激活，则UART应避免发送。

您可能希望查看 termios 手册页。

Answer 2

我认为这不是一个解决方案，而是添加：

tcflush(fd, TCIOFLUSH); // clear buffer

清除缓冲区似乎可以解决问题。但是，应该有一些更优雅和适当的解决方案。

Answer 3

由于“刷新”可能意味着清除缓冲区或等待直到所有字节发送完毕，因此引文来自https://linux.die.net/man/3/tcdrain

tcdrain（）等待，直到写入fd引用的对象的所有输出都已传输。

tcflush（）根据queue_selector的值，丢弃写入fd所引用但未发送的对象的数据，或已接收但未读取的数据

所以

tcdrain(fd); // Wait until transmission ends
tcflush(fd, TCOFLUSH); // Clear write buffer

linux c写完后刷新串口缓冲区

3 个答案: