#include <gdt.h>


#define GDT_ENTRIES 3

struct gdt_entry gdt[GDT_ENTRIES];
struct gdt_ptr gp;

extern void gdt_flush(uint32_t);

void gdt_install()
{
  gp.limit = (sizeof(struct gdt_entry) * GDT_ENTRIES) - 1;
  gp.base  = (uint32_t)&gdt;

  gdt_set_entry(0, 0, 0, 0, 0);                /* Null segment */
  gdt_set_entry(1, 0, 0xFFFFFFFF, 0x9A, 0xCF); /* Code segment */
  gdt_set_entry(2, 0, 0xFFFFFFFF, 0x92, 0xCF); /* Data segment */

  gdt_flush((uint32_t)&gp);
}

void gdt_set_entry(int num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran)
{
  gdt[num].base_low    = (base & 0xFFFF);
  gdt[num].base_middle = (base >> 16) & 0xFF;
  gdt[num].base_high   = (base >> 24) & 0xFF;

  gdt[num].limit_low   = (limit & 0xFFFF);
  gdt[num].granularity = (limit >> 16) & 0x0F;

  gdt[num].granularity |= (gran & 0xF0);
  gdt[num].access      = access;
}