/*

   CBREAK.C

*/
#include <stdio.h>
#include <dos.h>
#include <conio.h>
#include "cbreak.h"

#define CB_FAR far

#define BITSET(x, n) ( (((unsigned) x >> n) & 0x0001) == 1 ? 1 : 0 )

#define INT09   (0x0009)      /* Keyboard interrupt number */
#define INT1B   (0x001B)      /* CTRL+C interrupt number */
#define INT23   (0x0023)      /* CTRL+BREAK interrupt number */

#define ESC             (0x1B)        /* ASCII escape code */
#define SPACE           (0x20)        /* ASCII space  code */
#define SCANCODE_C      (0x2E)        /* Scan code for the "C" key */
#define CTRL_OFF_MASK   (0xFB)        /* CTRL+C bit mask */
#define CTRL_ON_MASK    (0x04)        /* CTRL+C bit mask */

#define KBDMEM  (0x0000041C)  /* Keybrd buffer tail pointer address */
#define KBDBUF  (0x0000041E)  /* Keyboard buffer address */
#define KBDFLAG (0x00000417)  /* Keyboard flag byte address */

#define KB_DATA 0x0060      /* Kbd port address  */


/*-------------------------------------------------------------------------*/
/*  Functions pointers */

void (interrupt CB_FAR *old_break_int09)(); /* Save old kbd handler */
void (interrupt CB_FAR *old_break_int1B)(); /* Save old ^C  handler */
void (interrupt CB_FAR *old_break_int23)(); /* Save old brk handler */

/*-------------------------------------------------------------------------*/
unsigned short CB_FAR * kbd_buf;
unsigned short CB_FAR * kbd_ctrl;
unsigned short CB_FAR * kbd_tail;

/*-------------------------------------------------------------------------*/
/* Interrupt service routines */


void interrupt CB_FAR break_int09(void);
void interrupt CB_FAR break_int1B(void);
void interrupt CB_FAR break_int23(void);

/*-------------------------------------------------------------------------*/

unsigned break_sem;              /* ^C was pressed then sem=1, else sem=0 */
unsigned break_installed = 0;

void break_Install(void)
{
   unsigned i;

   if ( break_installed != 0 )
      return;

   old_break_int09 = _dos_getvect( INT09 );
   old_break_int1B = _dos_getvect( INT1B );
   old_break_int23 = _dos_getvect( INT23 );

   _dos_setvect( INT09, break_int09 );
   _dos_setvect( INT1B, break_int1B );
   _dos_setvect( INT23, break_int23 );

   kbd_tail  = (unsigned short CB_FAR *)(long)KBDMEM;
   kbd_buf   = (unsigned short CB_FAR *)(long)KBDBUF;
   kbd_ctrl  = (unsigned short CB_FAR *)(long)KBDFLAG;

   for(i = 0; i < 16; i++)
      kbd_buf[i] = (unsigned) (0x3900 | SPACE);

   break_sem = 0;
   break_installed = 1;
}

void break_Remove(void)
{
   if ( break_installed == 0 )
      return;

   _dos_setvect( INT09, old_break_int09 );
   _dos_setvect( INT1B, old_break_int1B );
   _dos_setvect( INT23, old_break_int23 );

   break_installed = 0;
}

int break_IsCTRLC(void)
{
   return break_sem == 0 ? 0 : 1;
}


/*-------------------------------------------------------------------------*/
/* Interrupt service routines */


void interrupt CB_FAR break_int09( void )
{
   unsigned cell;       /* Data from kbd port 60h */
   unsigned indx = 0;

   _disable();

   cell = inp( KB_DATA );

   break_sem = 0;
   if ( BITSET(*kbd_ctrl, 2) && (cell & 0x0ff) == SCANCODE_C )
   {
      break_sem = 1;
      indx = ( *kbd_tail - (KBDBUF & 0x0ff) ) / 2;
      *kbd_ctrl &= CTRL_OFF_MASK;
   }

   old_break_int09();

   if ( break_sem != 0 )
   {
      *kbd_ctrl |= CTRL_ON_MASK;
      kbd_buf[indx] = CTRL_C_REPLACE;
   }
}



void interrupt CB_FAR break_int1B(void)
{
    /* New home for CTRL+C     */
}



void interrupt CB_FAR break_int23(void)
{
    /* New Home for CTRL+BREAK */
}


/*-------------------------------------------------------------------------*/

/* #define break_main */
#ifdef break_main

#define LOBYTE(x)  ( (unsigned char) ((unsigned) x & 0x00FF) )

void KbdHexDump( unsigned short CB_FAR *str )
{
   unsigned  j;

   printf("\n");
   for( j=0; j < 16; j++ )
   {
      if ( LOBYTE(str[j]) < 15 )
         printf("0");
      if ( str[j] == CTRL_C_REPLACE )
         printf("03 ");
      else
         printf("%x ", LOBYTE(str[j]));
   }
   printf("     ");
   for( j=0; j < 16; j++ )
   {
      if ( LOBYTE(str[j]) < SPACE )
         printf("%c", '.');
      else
         printf("%c", LOBYTE(str[j]));
   }
   printf("\n");

}


#include <time.h>
void main (void)
{
   unsigned ch;

   break_Install();

   ch = 0;

   while( ch != ESC )
   {
      printf("%ld\n", (long)clock());
      ch = getch();
      if ( ch == CTRL_C_REPLACE )
         printf("\nCtrl-C value\n");

      if ( break_IsCTRLC() )
         printf("\nCtrl-C key was pressed!\n");

      KbdHexDump( kbd_buf );
   }

   break_Remove();
}

#endif