#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <termios.h>

#define BAUD_RATE B9600

int main (void)
{
    fd_set read_flags,write_flags; // you know what these are
    struct timeval waitd;
    int thefd;             // The socket
    char outbuff[512];     // Buffer to hold outgoing data
    char inbuff[512];      // Buffer to read incoming data into
    int err;          // holds return values
    struct termios options;

    memset(&outbuff,0,sizeof(outbuff)); // memset used for portability
    //opening port
    thefd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY | O_ASYNC);
    if (thefd == -1) {
        // could not open port
        fprintf(stderr,"open_port: Unable to open %s\n", "/dev/ttyS0");
    } else {
        fcntl(thefd, F_SETFL, O_NDELAY);
        tcgetattr(thefd, &options);
        // BAUD rate
        cfsetispeed(&options, BAUD_RATE);
        cfsetospeed(&options, BAUD_RATE);
        // enable the receiver and set local mode...
        options.c_cflag |= (CLOCAL | CREAD);

        // no parity (8 in 1)
        options.c_cflag &= ~PARENB;
        options.c_cflag &= ~CSTOPB;
        options.c_cflag &= ~CSIZE;
        options.c_cflag |= CS8;

        // no flow controll
        //options.c_cflag &= ~CRTSCTS;    /* Also called CRTSCTS */

        // apply all changes immediately
        tcsetattr(thefd, TCSANOW, &options);
    }

    strcat(outbuff,"jarjam\n"); //Add the string jarjam to the output
    //buffer
    while(1) {
        waitd.tv_sec = 1;     // Make select wait up to 1 second for data
        waitd.tv_usec = 0;    // and 0 milliseconds.
        FD_ZERO(&read_flags); // Zero the flags ready for using
        FD_ZERO(&write_flags);
        FD_SET(thefd, &read_flags);
        if(strlen(outbuff)!=0) FD_SET(thefd, &write_flags);
        err=select(thefd+1, &read_flags,&write_flags,
                (fd_set*)0,&waitd);
        if(err < 0) continue;
        if(FD_ISSET(thefd, &read_flags)) { //Socket ready for reading
            FD_CLR(thefd, &read_flags);
            memset(&inbuff,0,sizeof(inbuff));
            if (read(thefd, inbuff, sizeof(inbuff)-1) <= 0) {
                close(thefd);
                break;
            }
            else printf("%s",inbuff);
        }
        if(FD_ISSET(thefd, &write_flags)) { //Socket ready for writing
            FD_CLR(thefd, &write_flags);
            write(thefd,outbuff,strlen(outbuff));
            memset(&outbuff,0,sizeof(outbuff));
        }
        // now the loop repeats over again
    }
}