Linux: How to open /dev/tty port

Hi Kemal,

first time, i confused little bit about a name of serial port. !now i can send data out to UART4 but i still have some problem from code below.

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

int main(){
    int file, count;
    if ((file = open("/dev/ttyS4", O_RDWR | O_NOCTTY | O_NDELAY))<0){
        perror("UART: Failed to open the file.\n");
        return -1;
    }
    struct termios options; // the termios structure is vital
    tcgetattr(file, &options); // sets the parameters associated with file
    // Set up the communications options:
    // 9600 baud, 8-bit, enable receiver, no modem control lines
    options.c_cflag = B9600 | CS8 | CREAD | CLOCAL;
    options.c_iflag = IGNPAR | ICRNL; // ignore partity errors, CR -> newline
    tcflush(file, TCIFLUSH); // discard file information not transmitted
    tcsetattr(file, TCSANOW, &options); // changes occur immmediately
    unsigned char transmit[18] = "Hello BeagleBone!"; // the string to send

    if ((count = write(file, &transmit,18))<0){ // send the string
        perror("Failed to write to the output\n");
        return -1;
    }

    usleep(100000); // give the Arduino a chance to respond
    unsigned char receive[100]; // declare a buffer for receiving data

    if ((count = read(file, (void*)receive, 100))<0){ // receive the data
        perror("Failed to read from the input\n");
        return -1;
    }
    if (count==0) printf("There was no data available to read!\n");
    else {
        printf("The following was read in [%d]: %s\n",count,receive);
    }

    close(file);
    return 0;
}

OUTPUT

Best regards,
Somkiat

You can refer to this example.