dsctbl.c

#include "head.h"




void init_gdtidt(void);
void set_segmdesc(struct SEGMENT_DESCRIPTOR *sd, unsigned int limit, int base, int ar);
void set_gatedesc(struct GATE_DESCRIPTOR *gd, int offset, int selector, int ar);
void load_gdtr(int size, int base);
void load_idtr(int size, int base);
void asm_inthandler21();
void asm_inthandler2c();
void asm_inthandler27();
void init_pic(void);

void init_gdtidt(void)
{
	//gdt 从0x270000 - 0x271fff 总共8192项
	struct SEGMENT_DESCRIPTOR *gdt = (struct SEGMENT_DESCRIPTOR*) 0x00270000;
	//idt 从0x26f800 - 0x26ffff 总共256个
	struct GATE_DESCRIPTOR *idt = (struct GATE_DESCRIPTOR*) 0x0026f800;
	int i;

	for(i = 0; i < 8192; i++){
		set_segmdesc(gdt + i, 0, 0, 0);
	}
	set_segmdesc(gdt + 1, 0xffffffff, 0x00000000, 0x4092);
	set_segmdesc(gdt + 2, 0x0007ffff, 0x00280000, 0x409a);
	load_gdtr(0xffff, 0x00270000);

	for(i = 0; i < 256; i++)
	{
		set_gatedesc(idt + i, 0, 0, 0);
	}

	load_idtr(LIMIT_IDT, ADR_IDT);

	set_gatedesc(idt + 0x21, (int) asm_inthandler21, 2 * 8, AR_INTGATE32);
	set_gatedesc(idt + 0x27, (int) asm_inthandler27, 2 * 8, AR_INTGATE32);
	set_gatedesc(idt + 0x2c, (int) asm_inthandler2c, 2 * 8, AR_INTGATE32);


	return;
}

void set_segmdesc(struct SEGMENT_DESCRIPTOR *sd, unsigned int limit, int base, int ar){
	if(limit > 0xfffff){
		ar |= 0x8000;
		limit /= 0x1000;
	}
	sd->limit_low = limit & 0xffff;
	sd->base_low = base & 0xffff;
	sd->base_mid = (base >> 16) &0xff;
	sd->access_right = ar & 0xff;
	sd->limit_high = ((limit >> 16) & 0x0f) | ((ar >> 8) & 0xf0);
	sd->base_high = (base >> 24) & 0xff;
	return;
}

void set_gatedesc(struct GATE_DESCRIPTOR *gd, int offset, int selector, int ar)
{
	gd->offset_low = offset & 0xffff;
	gd->selector = selector;
	gd->dw_count = (ar >> 8) & 0xff;
	gd->access_right = ar & 0xff;
	gd->offset_high = (offset >> 16) &0xffff;
	return;
}