How to read and write directly to a serial port & set baud rate etcetc. LINUX - DEBIAN

#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <sys/types.h>
 
#define BAUDRATE B38400
#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
char devicename[80];
long Baud_Rate = 38400;         // default Baud Rate (110 through 38400)
long BAUD;                      // derived baud rate from command line
long DATABITS;
long STOPBITS;
long PARITYON;
long PARITY;
int Data_Bits = 8;              // Number of data bits
int Stop_Bits = 1;              // Number of stop bits
int Parity = 0;                 // Parity as follows:
                  // 00 = NONE, 01 = Odd, 02 = Even, 03 = Mark, 04 = Space
int Format = 4;
FILE *input;
FILE *output;
int status;
 
main(int Parm_Count, char *Parms[])
{
   char version[80] = "       POSIX compliant Communications test program version 1.00 4-25-1999\r\n";
   char version1[80] = "          Copyright(C) Mark Zehner/Peter Baumann 1999\r\n";
   char version2[80] = " This code is based on a DOS based test program by Mark Zehner and a Serial\r\n";
   char version3[80] = " Programming POSIX howto by Peter Baumann, integrated by Mark Zehner\r\n";  
   char version4[80] = " This program allows you to send characters out the specified port by typing\r\n";
   char version5[80] = " on the keyboard.  Characters typed will be echoed to the console, and \r\n";
   char version6[80] = " characters received will be echoed to the console.\r\n";
   char version7[80] = " The setup parameters for the device name, receive data format, baud rate\r\n";
   char version8[80] = " and other serial port parameters must be entered on the command line \r\n";
   char version9[80] = " To see how to do this, just type the name of this program. \r\n";
   char version10[80] = " This program is free software; you can redistribute it and/or modify it\r\n";
   char version11[80] = " under the terms of the GNU General Public License as published by the \r\n";
   char version12[80] = " Free Software Foundation, version 2.\r\n";
   char version13[80] = " This program comes with ABSOLUTELY NO WARRANTY.\r\n";
   char instr[100] ="\r\nOn the command you must include six items in the following order, they are:\r\n";
   char instr1[80] ="   1.  The device name      Ex: ttyS0 for com1, ttyS1 for com2, etc\r\n";
   char instr2[80] ="   2.  Baud Rate            Ex: 38400 \r\n";
   char instr3[80] ="   3.  Number of Data Bits  Ex: 8 \r\n";
   char instr4[80] ="   4.  Number of Stop Bits  Ex: 0 or 1\r\n";
   char instr5[80] ="   5.  Parity               Ex: 0=none, 1=odd, 2=even\r\n";
   char instr6[80] ="   6.  Format of data received:  1=hex, 2=dec, 3=hex/asc, 4=dec/asc, 5=asc\r\n";
   char instr7[80] =" Example command line:  com ttyS0 38400 8 0 0 4 \r\n";
   char Param_strings[7][80];
   char message[90];
 
   int fd, tty, c, res, i, error;
   char In1, Key;
   struct termios oldtio, newtio;       //place for old and new port settings for serial port
   struct termios oldkey, newkey;       //place tor old and new port settings for keyboard teletype
   struct sigaction saio;               //definition of signal action
   char buf[255];                       //buffer for where data is put
   
   input = fopen("/dev/tty", "r");      //open the terminal keyboard
   output = fopen("/dev/tty", "w");     //open the terminal screen
 
   if (!input || !output)
   {
      fprintf(stderr, "Unable to open /dev/tty\n");
      exit(1);
   }
 
   error=0;
   fputs(version,output);               //display the program introduction
   fputs(version1,output);
   fputs(version2,output);
   fputs(version3,output);
   fputs(version4,output);
   fputs(version5,output);
   fputs(version6,output);
   fputs(version7,output);
   fputs(version8,output);
   fputs(version9,output);
   fputs(version10,output);
   fputs(version11,output); 
   fputs(version12,output);
   fputs(version13,output);
   //read the parameters from the command line
   if (Parm_Count==7)  //if there are the right number of parameters on the command line
   {
      for (i=1; i&#60Parm_Count; i++)  // for all wild search parameters
      {
         strcpy(Param_strings[i-1],Parms[i]);
      }
      i=sscanf(Param_strings[0],"%s",devicename);
      if (i != 1) error=1;
      i=sscanf(Param_strings[1],"%li",&Baud_Rate);
      if (i != 1) error=1;
      i=sscanf(Param_strings[2],"%i",&Data_Bits);
      if (i != 1) error=1;
      i=sscanf(Param_strings[3],"%i",&Stop_Bits);
      if (i != 1) error=1;
      i=sscanf(Param_strings[4],"%i",&Parity);
      if (i != 1) error=1;
      i=sscanf(Param_strings[5],"%i",&Format);
      if (i != 1) error=1;
      sprintf(message,"Device=%s, Baud=%li\r\n",devicename, Baud_Rate); //output the received setup parameters
      fputs(message,output);
      sprintf(message,"Data Bits=%i  Stop Bits=%i  Parity=%i  Format=%i\r\n",Data_Bits, Stop_Bits, Parity, Format);
      fputs(message,output);
   }  //end of if param_count==7
   if ((Parm_Count==7) && (error==0))  //if the command line entries were correct
   {                                    //run the program
      tty = open("/dev/tty", O_RDWR | O_NOCTTY | O_NONBLOCK); //set the user console port up
      tcgetattr(tty,&oldkey); // save current port settings   //so commands are interpreted right for this program
      // set new port settings for non-canonical input processing  //must be NOCTTY
      newkey.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
      newkey.c_iflag = IGNPAR;
      newkey.c_oflag = 0;
      newkey.c_lflag = 0;       //ICANON;
      newkey.c_cc[VMIN]=1;
      newkey.c_cc[VTIME]=0;
      tcflush(tty, TCIFLUSH);
      tcsetattr(tty,TCSANOW,&newkey);
 
      switch (Baud_Rate)
      {
         case 38400:
         default:
            BAUD = B38400;
            break;
         case 19200:
            BAUD  = B19200;
            break;
         case 9600:
            BAUD  = B9600;
            break;
         case 4800:
            BAUD  = B4800;
            break;
         case 2400:
            BAUD  = B2400;
            break;
         case 1800:
            BAUD  = B1800;
            break;
         case 1200:
            BAUD  = B1200;
            break;
         case 600:
            BAUD  = B600;
            break;
         case 300:
            BAUD  = B300;
            break;
         case 200:
            BAUD  = B200;
            break;
         case 150:
            BAUD  = B150;
            break;
         case 134:
            BAUD  = B134;
            break;
         case 110:
            BAUD  = B110;
            break;
         case 75:
            BAUD  = B75;
            break;
         case 50:
            BAUD  = B50;
            break;
      }  //end of switch baud_rate
      switch (Data_Bits)
      {
         case 8:
         default:
            DATABITS = CS8;
            break;
         case 7:
            DATABITS = CS7;
            break;
         case 6:
            DATABITS = CS6;
            break;
         case 5:
            DATABITS = CS5;
            break;
      }  //end of switch data_bits
      switch (Stop_Bits)
      {
         case 1:
         default:
            STOPBITS = 0;
            break;
         case 2:
            STOPBITS = CSTOPB;
            break;
      }  //end of switch stop bits
      switch (Parity)
      {
         case 0:
         default:                       //none
            PARITYON = 0;
            PARITY = 0;
            break;
         case 1:                        //odd
            PARITYON = PARENB;
            PARITY = PARODD;
            break;
         case 2:                        //even
            PARITYON = PARENB;
            PARITY = 0;
            break;
      }  //end of switch parity
       
      //open the device(com port) to be non-blocking (read will return immediately)
      fd = open(devicename, O_RDWR | O_NOCTTY | O_NONBLOCK);
      if (fd < 0)
      {
         perror(devicename);
         exit(-1);
      }
 
      //install the serial handler before making the device asynchronous
      saio.sa_handler = signal_handler_IO;
      sigemptyset(&saio.sa_mask);   //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 = BAUD | CRTSCTS | DATABITS | STOPBITS | PARITYON | PARITY | CLOCAL | CREAD;
      newtio.c_iflag = IGNPAR;
      newtio.c_oflag = 0;
      newtio.c_lflag = 0;       //ICANON;
      newtio.c_cc[VMIN]=1;
      newtio.c_cc[VTIME]=0;
      tcflush(fd, TCIFLUSH);
      tcsetattr(fd,TCSANOW,&newtio);
 
      // loop while waiting for input. normally we would do something useful here
      while (STOP==FALSE)
      {
         status = fread(&Key,1,1,input);
         if (status==1)  //if a key was hit
         {
            switch (Key)
            { /* branch to appropiate key handler */
               case 0x1b: /* Esc */
                  STOP=TRUE;
                  break;
               default:
                  fputc((int) Key,output);
//                  sprintf(message,"%x ",Key);  //debug
//                  fputs(message,output);
                  write(fd,&Key,1);          //write 1 byte to the port
                  break;
            }  //end of switch key
         }  //end if a key was hit
         // after receiving SIGIO, wait_flag = FALSE, input is available and can be read
         if (wait_flag==FALSE)  //if input is available
         {
            res = read(fd,buf,255);
            if (resl)
            {
               for (i=0; i<res; i++)  //for all chars in string
               {
                  In1 = buf[i];
                  switch (Format)
                  {
                     case 1:         //hex
                        sprintf(message,"%x ",In1);
                        fputs(message,output);
                        break;
                     case 2:         //decimal
                        sprintf(message,"%d ",In1);
                        fputs(message,output);
                        break;
                     case 3:         //hex and asc
                        if ((In1) || (In1­))
                        {
                           sprintf(message,"%x",In1);
                           fputs(message,output);
                        }
                        else fputc ((int) In1, output);
                        break;
                     case 4:         //decimal and asc
                     default:
                        if ((In1) || (In1­))
                        {
                           sprintf(message,"%d",In1);
                           fputs(message,output);
                        }
                        else fputc ((int) In1, output);
                        break;
                     case 5:         //asc
                        fputc ((int) In1, output);
                        break;
                  }  //end of switch format
               }  //end of for all chars in string
            }  //end if resX
//            buf[res]=0;
//            printf(":%s:%d\n", buf, res);
//            if (res==1) STOP=TRUE; /* stop loop if only a CR was input */
            wait_flag = TRUE;      /* wait for new input */
         }  //end if wait flag == FALSE
 
      }  //while stop==FALSE
      // restore old port settings
      tcsetattr(fd,TCSANOW,&oldtio);
      tcsetattr(tty,TCSANOW,&oldkey);
      close(tty);
      close(fd);        //close the com port
   }  //end if command line entrys were correct
   else  //give instructions on how to use the command line
   {
      fputs(instr,output);
      fputs(instr1,output);
      fputs(instr2,output);
      fputs(instr3,output);
      fputs(instr4,output);
      fputs(instr5,output);
      fputs(instr6,output);
      fputs(instr7,output);
   }
   fclose(input);
   fclose(output);
}  //end of main
 
/***************************************************************************
* signal handler. sets wait_flag to FALSE, to indicate above loop that     *
* characters have been received.                                           *
***************************************************************************/
 
void signal_handler_IO (int status)
{
//    printf("received SIGIO signal.\n");
   wait_flag = FALSE;
}
                                              

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