/***                 LISTING 4                ***/
/***                                          ***/
/***                  intin.c                 ***/
/*** **************************************** ***/
/***    INTERRUPT TO HANDLE DATA RECEIVED     ***/
/*** **************************************** ***/
#include "serial.h"

extern  int portbase;

static  char  buf[SBUFSIZ];
static  int  bufptr   = 0;
static  int  byteptr  = 0;

extern  void  (interrupt far *oldvect)();

void interrupt far ReceiveData(void)
{

  if((inp(portbase + IIR) & RX_MASK) == RX_ID)
    {
     buf[bufptr++] = inp(portbase + RXR);

     if(bufptr >= SBUFSIZ)
	bufptr = 0;
    }

/***     Signal end of hardware interrupt     ***/

  outp(ICR,EOI);

  (*oldvect)();
}

/*** **************************************** ***/
/***         GRABS A BYTE FROM BUFFER         ***/
/*** **************************************** ***/
int  IntSerialIn(void)
{
  int Char_Value;

  if (byteptr == bufptr)
    {
     return (-1);
    }

  Char_Value = (int)buf[byteptr++];

  if(byteptr >= SBUFSIZ)
     byteptr = 0;

  return (Char_Value);
}