/******************************************************************
 *    idt.h  -  INTERRUPT DESCRIPTOR TABLE                        *
 *      Contains structures and function declarations for IDT     *
 ******************************************************************/
#include <system.h>
#include "idt.h"

/* Declare an IDT of 256 entries. Although we will only use the
*  first 32 entries in this tutorial, the rest exists as a bit
*  of a trap. If any undefined IDT entry is hit, it normally
*  will cause an "Unhandled Interrupt" exception. Any descriptor
*  for which the 'presence' bit is cleared (0) will generate an
*  "Unhandled Interrupt" exception */
struct idt_entry idt[256];
struct idt_ptr idtp;

/* Use this function to set an entry in the IDT. Alot simpler
*  than twiddling with the GDT ;) */
void i86_idt_set_gate(unsigned char num, unsigned long base, unsigned short sel, unsigned char flags)
{
    /* The interrupt routine's base address */
    idt[num].base_lo = (base & 0xFFFF);
    idt[num].base_hi = (base >> 16) & 0xFFFF;

    /* The segment or 'selector' that this IDT entry will use
    *  is set here, along with any access flags */
    idt[num].sel = sel;
    idt[num].always0 = 0;
    idt[num].flags = flags;
}

struct idt_entry* i86_idt_get_gate(unsigned char num)
{
      return &idt[num];
}

/* Installs the IDT */
void i86_idt_install()
{
    /* Sets the special IDT pointer up, just like in 'gdt.c' */
    idtp.limit = (sizeof (struct idt_entry) * 256) - 1;
    idtp.base = (unsigned int)&idt;

    /* Clear out the entire IDT, initializing it to zeros */
    memset (&idt, 0, sizeof(struct idt_entry) * 256);

    /* Points the processor's internal register to the new IDT */
    i86_idt_load();
}