如何使用Termios在socat数据传输环路上发送字节

Question

$ socat -d -d pty pty

$ cat /dev/pts/0 | xxd
$ read -r line < /dev/pts/0
$ echo $line

#define BAUD_RATE B9600
#define PORT_NAME "/dev/pts/2"

/* Serial Connection Manager */
struct termios tty;
int fd;

int main(){
  /*
  O_RDWR: read/write access to serial port
  O_NOCTTY: No terminal will control the process
  O_NDELAY: Non-blocking, returns immediately
  */
  fd = open(PORT_NAME, O_RDWR | O_NOCTTY | O_NDELAY);
  printf("%s\n", PORT_NAME);
  if (fd == -1) {
    printf("Error in opening serial port\n");
    return -1;
  }
  else
    printf("Port opened successfully\n");

  tcgetattr(fd, &tty); // get current attrs of serial port
  // raw mode of terminal driver
  //cfsetispeed(&tty, BAUD_RATE);
  //cfsetospeed(&tty, BAUD_RATE);
  cfmakeraw(&tty);

  // set additional control modes
  cfsetspeed(&tty, (speed_t) BAUD_RATE);
  tty.c_cflag &= ~CSTOPB; //1 stop bit
  tty.c_cflag &= ~CRTSCTS; //disable hardware flow control
  tty.c_cflag |= CLOCAL; //ignore modem control lines
  tty.c_cflag |= CREAD; //enable receiver

  if((tcsetattr(fd, TCSANOW, &tty)) != 0){
    printf("Error in setting attributes\n");
    close(fd);
    return -1;
  }
  else
    printf("BaudRate = %d\nStopBits = 1\nParity = Odd\n", BAUD_RATE);

  sleep(1); // wait for configuration
  tcflush(fd, TCIOFLUSH);

  char buf[3] = "abc";
  int bytes_written = write(fd, buf, 3);
  printf("Bytes written: %d", bytes_written);
  close(fd);
  return 0;
}

运行我的程序会得到以下输出：

/dev/pts/2
Port opened successfully
BaudRate = 13
StopBits = 1
Parity = Odd
Bytes written: 3

所以我知道这些字节在哪里，因为write（）不会返回-1。

Answer 1

您的代码与真实和虚拟的串行端口都很好。

您需要注意socat输出：

$ socat -d -d pty pty
2019/07/18 07:55:45 socat[8144] N PTY is /dev/pts/2
2019/07/18 07:55:45 socat[8144] N PTY is /dev/pts/3
2019/07/18 07:55:45 socat[8144] N starting data transfer loop with FDs [5,5] and [7,7]

然后侦听对的第一个端口：

$ cat /dev/pts/2

$ minicom -D /dev/pts/2 -b 9600