/***********************************************************************
*
*	Name:   sys_sppt.c
*
*	Purpose:  Support Routines for Modules 3 and 4 of MPX-PC
*
*	Sample Call:
*                     sys_init()
*                     sys_exit()
*
* 	Procedures In Module:
*                     sys_init - Sets up interrupt vector 60 for MPX-PC
*                     sys_exit - Resets interrupt vector 60 and exits to DOS
*
*
****************************************************************************/

#include <stdio.h>
#include <dos.h>
#include "mpx.h"

void interrupt (*vect60)();  /* Storage for DOS int 60h */
			                 /* interrupt vector.       */

void sys_init()
{
    /* set up interrupt vector for MPX sys_calls */

	vect60 = getvect(0x60);
	setvect(0x60,&sys_call);
}


void sys_exit()
{
	/* restore interrupt vector 60 and exit */

	setvect(0x60,vect60);
	exit();
}


void interrupt dispatch()
{
 /* your dispatcher code */
 if (ready_queue == NULL) {
   sys_exit();
 } else {
   cop = ready_queue; // make the front of the queue the running process
   remove_pcb(&ready_queue, cop);
   _SP = cop->stack_ptr;
 }
}


void interrupt sys_call()
{
	struct parm {
		int op_number;
		int op_type;
		char *buffer;
		int *length;
	};

	static struct parm *parm_add;

	/* Save stack pointer for current process */
	cop->stack_ptr = _SP;

	/* Get address of sys_call parameters */
	parm_add = _SP + 0x1c; // parameter offset = 0x1C

	/* Note that you should save this parameter address
	   somewhere in the pcb as suggested below*/
	cop->parm_add = parm_add;

	// find out if the process wants to die... and kill it
	if(parm_add->op_number != EXIT_CODE) {
	  insert_pcb(&ready_queue, cop, 0);
	}

	dispatch();
}