/* asm.h */
#ifndef _ASM_H
#define _ASM_H

typedef struct{
	unsigned short limit;
	unsigned short base;
} gdtptr;

typedef struct 
{
	unsigned short limit_low;
	unsigned short base_low;
	unsigned char base_middle;
	unsigned char access;
	unsigned char granularity;
	unsigned char base_high;
} gdtentry;


volatile gdtptr gdtaddr;

void pmode(void);

#endif

/* <EOF> */



/* ----- protected_mode.S --- */
.text
.globl _pmode, pmode

pmode:
_pmode:
	
	cli /* atomic */ 
	lgdt gdtaddr /* point it */
	mov %eax, %cr0
	or %eax, 1
	mov %cr0, %eax

	jmp somewhere_else /* to clear out the instruction prefetch queue */
	nop
	
somewhere_else:	
	sti /* end of atomic */
	ret

/* <EOF> */

/* -- kern_main.c -- */

#include <multiboot.h>
#include <asm.h>
void kern_main(unsigned long mbpointer)
{
	volatile unsigned char *video;
	video = (unsigned char *) 0xB8052;
	
	*video = 0x48 & 0xFF;
	*(video+2) = 0x49 & 0xFF;
	gdtentry mygdt[3];
	
	mygdt[0].limit_low = 0;
	mygdt[0].base_low = 0;
	mygdt[0].base_middle = 0;
	mygdt[0].access = 0;
	mygdt[0].granularity =  0;
	mygdt[0].base_high = 0;
	
	gdtaddr.base = &mygdt;
	gdtaddr.limit = (3 * sizeof(gdtentry)) - 1;

	mygdt[1].limit_low = (0xFFFFFFFF & 0xFFFF);
	mygdt[1].base_low = 0;
	mygdt[1].base_middle = 0;
	mygdt[1].access = 0x9A;
	mygdt[1].granularity =  ((0xFFFFFFFF >> 16) & 0x0F);
	mygdt[1].granularity |= (0xCF & 0xF0);
	mygdt[1].base_high = 0;
	
	mygdt[2].limit_low = (0xFFFFFFFF & 0xFFFF);
	mygdt[2].base_low = 0;
	mygdt[2].base_middle = 0;
	mygdt[2].access = 0x92;
	mygdt[2].granularity =  ((0xFFFFFFFF >> 16) & 0x0F);
	mygdt[2].granularity |= (0xCF & 0xF0);
	mygdt[2].base_high = 0;
	
	pmode();
	*(video+8) = 0x4A & 0xFF;
}

/* <EOF> */