#include <stdio.h>
#include <conio.h>
#include <dos.h>

#ifdef __cplusplus
    #define __CPPARGS ...
#else
    #define __CPPARGS
#endif


#define	MAXKEYQUEUE	0x40
static	char	kqQueue[MAXKEYQUEUE];	// 队列
static	int	kqFirst = 0;	// 指向首个数据
static	int	kqLast = 0;	// 指向首个空位
static	int	kqCount = 0;	// 该队列有多少元素

#define KSC_PRESS	0x80
#define KSC_DATAMASK	0x7F
#define	KSC_EXTEND	0xE0

#define	KSC_ESC	1

void interrupt get_out(__CPPARGS);    /* interrupt prototype */

void interrupt (*oldfunc)(__CPPARGS); /* interrupt function pointer */


int main(void)
{
	unsigned char	byKey;
	int	iEscCount=0;

	puts("Esc*3: Exit\n");

	/* save the old interrupt */
	oldfunc  = _dos_getvect(9);

	/* install interrupt handler */
	_dos_setvect(9,get_out);

	/* do nothing */
	while (iEscCount < 3){
		/* show key queue */
		while(kqCount > 0){
			/* get curent ScanCode */
			__asm	cli;
				byKey = kqQueue[kqFirst++];
				if (kqFirst >= MAXKEYQUEUE)	kqFirst -= MAXKEYQUEUE;
				kqCount--;
			__asm	sti;

			/* show */
			printf("%X\t", byKey);

			/* check Esc */
			if (byKey & KSC_PRESS)	{
				if (KSC_ESC == (byKey & KSC_DATAMASK))	{
					iEscCount++;
					if (2 == iEscCount){
						clrscr();
					}
				}else	{
					iEscCount = 0;
				}
			}
		}
	};

	/* restore to original interrupt routine */
	_dos_setvect(9,oldfunc);

	puts("Success");
	return 0;
}

void interrupt get_out(__CPPARGS)
{
	{
		unsigned char byKey;

		/* get ScanCode */
		byKey = inportb(0x60);

		/* add to key queue */
		if (kqCount < MAXKEYQUEUE){
			kqQueue[kqLast++] = byKey;
			if (kqLast >= MAXKEYQUEUE)	kqLast -= MAXKEYQUEUE;
			kqCount++;
		}
	}
	oldfunc(__CPPARGS);
}