indos.c

操作系统：用C++编写的时间片轮转法

/* INDOS.C-Functions to manage DOS flags */

#include <stdlib.h>
#include <dos.h>

#define GET_INDOS 0x34
#define GET_CRIT_ERR 0x5d06

char far* indos_ptr=0;
char far* crit_err_ptr=0;

int dosBusy(void);
void initInDos(void);

/* initInDos 
 * This Funtion to get the address of INDOS and CRIT_ERR flags
 */
void initInDos(void)
{
	union REGS regs;
	struct SREGS segregs;

	/* get the address of INDOS flag */
	regs.h.ah = GET_INDOS;
	intdosx(&regs,&regs,&segregs);
	indos_ptr = MK_FP(segregs.es,regs.x.bx);

	/* get the address of CRIT_ERR flag */ 
	if(_osmajor < 3)
		crit_err_ptr = indos_ptr+1;
	else if(_osmajor == 3 && _osminor == 0)
		crit_err_ptr = indos_ptr-1;
	else{
		regs.x.ax = GET_CRIT_ERR;
		intdosx(&regs,&regs,&segregs);
		crit_err_ptr = MK_FP(segregs.ds,regs.x.si);
	}
}

/* dosBusy
 * Function return non_zero is busy
 */
int dosBusy(void)
{
	if(indos_ptr && crit_err_ptr)
		return (*indos_ptr || *crit_err_ptr);
	else
		return(-1);		/* initInDos() hasn't been called */
}