Linux c写入后刷新串行缓冲区

linux c flush serial buffer after writing

本文关键字：缓冲区 刷新 Linux      更新时间：2023-10-16

问题很简单。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…但是我想不出来!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, "ATZn", 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:%dn", 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;
}

任何想法?

已通过设置"CRTSCTS"使能CTS硬件流控。这意味着如果输入到UART的CTS不是活动的，则UART应该避免发送。

您可能需要大致浏览一下术语手册页。

我不认为这是一个解决方案，但添加:

tcflush(fd, TCIOFLUSH); // clear buffer
用

清除缓冲区似乎能达到目的。然而，应该有一些更优雅、更合适的解决方案。

Since "可以表示清除缓冲区或等待直到所有字节被发送，这里引用https://linux.die.net/man/3/tcdrain

tcdrain()等待所有写入fd所引用对象的输出都传输完毕。

tcflush()丢弃写入fd引用的对象但未发送的数据，或接收到但未读取的数据，具体取决于queue_selector

的值。

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