#include <stdio.h>
#include <dos.h>
#include <string.h>
#include <stdlib.h>
#include <conio.h>
#include <time.h>

#define B1200  0x60
#define B2400  0x30
#define B4800  0x18
#define B9600  0x0c
#define B19200 0x06
#define PNONE  0x00
#define PEVEN  0x18        //bit 3,4
#define PODD   0x08        //bit 3
#define DATA7  0x02        //bit_end
#define DATA8  0x03        //bit0,1
#define STOP1  0x00
#define STOP2  0x40        //bit 2

#define PORT 0x3f8
#define TDR  PORT       //Transmit Data Reg
#define RDR  PORT       //Receive Data Reg
#define IER  PORT+1     //Interrupt Enable Reg
#define IIR  PORT+2     //Interrupt Identification Reg
#define LCR  PORT+3     //Line Control Reg
#define MCR  PORT+4
#define LSR  PORT+5     //Line Status Reg
#define PIC8259 0x21    //Mask Interrupt
#define IRQ4 0x0c

#define buffer_size 135
#define buffer_empty (head==tail)
#define ESC 0x1B
#define STX 0x02
#define EOT 0x04
#define ACK 0x06
#define NACK 0x08
#define END 0x10

char data;
char buffer[buffer_size];
int head=0;
int tail=0;

char rec_ch(void);
void sendchar(char ch);
void send_ch(char ch);
void interrupt (*oldhandler)();
void sendfile(time_t *t_end,time_t *t_start,double *fsize,int *numofframe,int *errorframe );
void receivefile(time_t *t_end,time_t *t_start,double *fsize,int *numofframe,int *errorframe );

void interrupt handler(void)
{
  unsigned char reg_IIR;
  unsigned char regLSR;
  disable();
  reg_IIR=inportb(IIR);
  reg_IIR&=0x06;                   //Read LSR, check line error
  if (reg_IIR==0x04)               //Data Received
  {                                //Read data from RDR
    do{
    regLSR=inportb(LSR);
    regLSR&=0x01;
    }    while(regLSR==0x00);
    buffer[head]=inportb(RDR);
    head++;

    if (head==buffer_size)
     head=0;
  }

  outportb(0x20,0x20);          //tell 8259 end of interrupt
  enable();                     //enable interrupt
}

void setcom_mode(unsigned char speed,unsigned char parity,
unsigned char data,unsigned char stop)
{
  unsigned char regLCR;
  regLCR=inportb(LCR);
  regLCR|=0x80;
  outportb(LCR,regLCR);
  outportb(TDR,speed);        //set baudrate
  outportb(IER,0x00);
  regLCR&=0x00;
  regLCR|=parity;
  regLCR|=data;
  regLCR|=stop;
  outportb(LCR,regLCR);
}

void setcom_int(void)
{
  unsigned char IRQmask;
  unsigned char regIER;
  oldhandler=getvect(IRQ4);         //save the old interrupt vector
  setvect(IRQ4,handler);            //install new interrupt handler
  outportb(MCR,0x0f);               //enable 8250 interrupt
  outportb(IER,0x00);
  IRQmask=inportb(PIC8259);
  IRQmask&=0xef;                    //enable COM1
  outportb(PIC8259,IRQmask);
}

void sendchar(char ch)
{
  unsigned char regIER;
  unsigned char regLSR;
  data=ch;
  do{
  regLSR=inportb(LSR);
  regLSR&=0x20;
  }  while(regLSR!=0x20);         //send next byte to THR
  outportb(PORT,ch);
}

/* receive character from terminal buffer */
char rec_ch()
{
  char ch;
  unsigned char regIER;
  int count=0;
  do{
  regIER=inportb(IER);
  regIER|=0x01;
  outportb(IER,regIER);
  count++;
  }  while(buffer_empty && count<15000);
  if (count<15000)
  {
  ch=buffer[tail];
  tail++;
  if (tail==buffer_size)
    tail=0;
  return(ch);
  }
  else
  {
    return(NULL);
  }
}



void sendfile(time_t *t_end,time_t *t_start,double *fsize,int *numofframe,int *errorframe )
{
    char ch,msg,already,frame[124],frame_num='0';
    int n,bcc=0,nbcc,numinarr=0,retransmit=0;
    FILE *in;
    char file_name[50];


    do{
         printf("Enter file name : ");
        scanf("%s", file_name);
        in = fopen(file_name, "r");

      }while(in== NULL);
  

    system("cls");
    setcom_int();
    setcom_mode(B9600,PNONE,DATA8,STOP1);              //intialize the com port

    while(1)
    {
          sendchar(ACK);
          if((ch=rec_ch())==ACK)
          {
            printf("Start sending file..\n");
            *t_start=time(NULL);                                     //the starting time of transmission
            break;
          }
          else
          {
            retransmit=retransmit+1;
            if (retransmit==200)                                        //limit the number of retransmit
             {    
                printf("\nTime out error!\n");
                return;
              }
          }
       }


    while(1)
    {

     if(((ch=rec_ch())==ACK)&&(!feof(in)))
     {
         retransmit =0;
         if(frame_num=='1')                               //change the frame no. for the checking of receiver
               frame_num='0';
         else if(frame_num=='0')
                 frame_num='1';
        
     for(n=0,numinarr=0,bcc=0;n<124;n++)
       {
       if (!feof(in))
         {
         msg=fgetc(in);

         if(msg!=-1)
           {
               frame[numinarr]=msg;          //save data in to the frame
               (*fsize)++;
               bcc+=frame[numinarr];      //sum of all data bits
             numinarr++;
        }
         }
       }
         nbcc=~bcc;         //2 complements
         nbcc++;

       sendchar(STX);
       sendchar(frame_num);
       sendchar(nbcc);
       printf("Frame %d Success\n", *numofframe);
       (*numofframe)++;
       for(n=0;n<numinarr;n++)
       {
        sendchar(frame[n]);           //send data bit of frame
       }
       sendchar(EOT);
       *t_end=time(NULL);
       }
       if((ch==NACK)||((difftime(time(NULL),*t_end))>1.0))
       {
      sendchar(STX);
      (*numofframe)++;   //accumulate no of frame we sent
      (*errorframe)++;     //accumulate no of error frame we sent
      sendchar(frame_num);
      sendchar(nbcc);
       for(n=0;n<numinarr;n++)
       {
        sendchar(frame[n]);                      //retrnasmit the frame which ocurr error before
       }
      sendchar(EOT);
       }
      if(feof(in))
     sendchar(END);
      if(ch==END)
      {
          *t_end=time(NULL);                // end time of transmission
          fclose(in);
          printf("\n\nThe transmission is completed.\n\n");
          return;
      }
      
    printf("retransmit : %d\n", retransmit);
    retransmit=retransmit+1;                               // calculate the no of retransmission
    if (retransmit==200)
      {     printf("\nTransmission time out error!\n");
        return;
      }
    
    }
  
}

void receivefile(time_t *t_end,time_t *t_start,double *fsize,int *noofframe,int *errorframe)
{
  char ch,msg,already,frame[124],bcc,nbcc,frame_num,seq_num='0';
  int n,numinarr,retransmit=0;
  FILE  *out;
  char file_name[50];

    do{
        printf("\nEnter file name: ");
        scanf("%s", file_name);
        out = fopen(file_name, "w");
    }while(out == NULL);
    
    system("cls");
    setcom_int();
    setcom_mode(B9600,PNONE,DATA8,STOP1);     //initialize the com port
    
     while(1)
     {

    ch = rec_ch();
    if (ch==ACK)
    {
    sendchar(ACK);
    printf("Receiving...\n");
    sendchar(ACK);
    *t_start=time(NULL);              // start of the receipt
    break;
    }
      else
      {
    retransmit=retransmit+1;
    if (retransmit==200)
      {     printf("\nRecieve time out error!\n");     //limit the number of retransmit
        return;
      }
      }
     }
     while(1)
     {
    if((ch=rec_ch())==STX)
        {
            retransmit=0;
            frame_num = rec_ch();
            nbcc = rec_ch();
            printf("Frame : %d success\n", *noofframe);
            (*noofframe)++;
            for(n=0,numinarr=0,bcc=0;n<124;n++)
            {
            ch=rec_ch();
            if (ch!=EOT)
                {
                    frame[numinarr]=ch;              // receive the data bit of frame
                    bcc+=frame[numinarr];          //sum of the data bit
                    numinarr++;
                }
            else
              break;
            }
            nbcc=~nbcc;               // 2 complement
            nbcc++;
            if (bcc==nbcc)           //error checking (BCC)
            {
                if (frame_num!=seq_num)
                {
                  seq_num=frame_num;
                  for (n=0;n<numinarr;n++, (*fsize)++)
                  {
                  fputc(frame[n], out);            // put the data into the file
                  }

                  for(n=0;n<numinarr;n++)
                  frame[n]=NULL;                  
                }
            sendchar(ACK);
            }
        else
            {
            sendchar(NACK);
            (*errorframe)++;                          // send Negative ACK to transmitor if error is occured
            }
            if (ch==EOT)
                   ch=rec_ch();
        }
  
    if ((ch==END))
    {
        *t_end=time(NULL);      //end of the receipt
        sendchar(END);            
        fclose(out);
        printf("\n\nRecevicing file complete\n\n");

          return;
    }
       else
       {
    retransmit=retransmit+1;
    if (retransmit==200)
      {     printf("\nRecieve time out error!\n");          // calculate the no of retransmission
        return;
      }

       }
      }


}
void main()
{
    char indicator;
    time_t t_end=0,t_start=0;
    double fsize=0;
    int numofframe=0;
    int errorframe=0;

    system("cls");

    printf(   "If you want to send file, Press S             \n");
    printf(   "If you are going to receive file, Press R          \n");

    scanf("%c",&indicator);
    if (indicator=='S'  ||indicator=='s' )
        sendfile(&t_end, &t_start, &fsize, &numofframe, &errorframe);
    else if (indicator=='R' || indicator=='r' )
        receivefile(&t_end, &t_start, &fsize, &numofframe, &errorframe);

/* Show output information*/

    printf("\n==================================\n");
    printf("Total Time consumed: %f s\n",difftime(t_end,t_start));
    printf("Total size of the file: %f bytes\n",fsize);
    printf("Total no. of frame : %d\n",numofframe);
    printf("Total no. of frame without error: %d\n", numofframe-errorframe);
    printf("Total no. of frame with error: %d\n",errorframe);
    printf("\n==================================\n");
      setvect(IRQ4,oldhandler);  //reset the old int. handler


    system("PAUSE");

}