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Code: Select all

[GLOBAL hwint00]
[extern _timer_handler]
hwint00:
	REG_SAVE
	cli
    call _timer_handler
	mov dx,20h
	mov al,20h
	out dx,al
	REG_RESTORE_MASTER
	ret ; shouldn't get here, but...

%macro REG_SAVE 0
	cld
	pushad
	push ds
	push es
	push fs
	push gs
	mov eax,[cPROC] ;put the adress of the struct of CURRENT PROCESS in eax.(the CONTENT of pointer p)
	mov [eax],esp ;save esp in the location of esp in the CURRENT PROCESS-STRUCT.
	lea eax,[kstackend] ; switch to the kernel's own stack.
	mov esp,eax
%endmacro

%macro REG_RESTORE_MASTER 0
	mov eax,[cPROC] ;put adress of struct of current process in eax.
	mov esp,[eax] ;restore adress of esp.
	mov ebx,[eax+8];put content of the k-stack field into ebx.
	mov [cTSS+4],ebx ;update system tss.
	mov al,0x20
	out 0x20,al
	pop gs
	pop fs
	pop es
	pop ds
	popad
	iretd
%endmacro

Code: Select all

#include <system.h>

#define KSTACKTOP 1024
#define USTACKTOP 1024

typedef struct {
	uint_t esp;
	uint_t ss;
	uint_t kstack;
	uint_t ustack;
	uint_t cr3;
	ulong_t PADDING;
	uint_t pid;
	uchar_t name[32];
} pdata_t;

typedef struct {
	ushort_t	backlink, __blh;
	uint_t		esp0;
	ushort_t	ss0, __ss0h;
	uint_t		esp1;
	ushort_t	ss1, __ss1h;
	uint_t		esp2;
	ushort_t	ss2, __ss2h;
	uint_t		cr3;
	uint_t		eip;
	uint_t		eflags;
	uint_t		eax, ecx, edx, ebx;
	uint_t		esp, ebp, esi, edi;
	ushort_t	es, __esh;
	ushort_t	cs, __csh;
	ushort_t	ss, __ssh;
	ushort_t	ds, __dsh;
	ushort_t	fs, __fsh;
	ushort_t	gs, __gsh;
	ushort_t	ldt, __ldth;
	ushort_t	trace, bitmap;
} tss_t;

tss_t cTSS;
pdata_t processes[32];
pdata_t* cPROC;
uint_t procnum = 1;
unsigned char kstacks[32][KSTACKTOP];
unsigned char stacks[32][USTACKTOP]; 

void init_task( int task , unsigned epoint )
{
	uint_t *stacksetup;
	stacksetup=(uint_t*)&kstacks[task][KSTACKTOP]; //esp0
	 stacksetup-- ;         //SS
	*stacksetup--=0x0202;  //flags
	*stacksetup--=0x08;    // CS
	*stacksetup--=epoint;  // Instruction pointer
	*stacksetup--= 0;      //error code
	*stacksetup--=0x20;    // interupt no.
	
	*stacksetup--=0;    //ebp
	*stacksetup--=0;    //esp
	*stacksetup--=0;    //edi
	*stacksetup--=0;    //esi
	*stacksetup--=0;    //edx
	*stacksetup--=0;    //ecx
	*stacksetup--=0;    //ebx
	*stacksetup--=0;    //eax
	
	*stacksetup--=0x20; //ds
	*stacksetup--=0x20; //es
	*stacksetup--=0x20; //fs
	*stacksetup=  0x20; //gs
	
	//filling in the struct.
    processes[task].esp=(uint_t)stacksetup;
    processes[task].ss=0x10;
    processes[task].kstack=(uint_t)&kstacks[task][KSTACKTOP];
    processes[task].ustack=(uint_t)&stacks[task][USTACKTOP];
	processes[task].PADDING = (ulong_t)"PUDDING!";
	processes[task].pid = task;
	
}

void schedule()
{
	//putch('s');
	++procnum;
	if (procnum > 3) {procnum = 1;}
	cPROC = &processes[procnum];
}

void t1() {putch('1');}
void t2() {putch('2');}
void t3() {putch('3');}

void mtask_init()
{
	init_task(1,(unsigned)t1);
	init_task(2,(unsigned)t2);
	init_task(3,(unsigned)t3);
}

Code: Select all

void timer_handler()
{
    ++timer_ticks;
    if (timer_ticks % 18 == 0)
    {
		++seconds;
		if (seconds % 60 == 0)
		{
			++minutes;
		}
    }
	schedule();
}