text: #include "system.h"
  
  /* Defines an IDT entry */
  struct idt_entry
  {
      unsigned short base_lo;
      unsigned short sel;        /* Our kernel segment goes here! */
      unsigned char always0;     /* This will ALWAYS be set to 0! */
      unsigned char flags;       /* Set using the above table! */
      unsigned short base_hi;
  } __attribute__((packed));
  
  struct idt_ptr
  {
      unsigned short limit;
      unsigned int base;
  } __attribute__((packed));
  
  /* 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;
  
  /* This exists in 'start.asm', and is used to load our IDT */
  extern void idt_load();
  /* Use this function to set an entry in the IDT. Alot simpler
  *  than twiddling with the GDT ;) */
  void 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;
  }
  
  /* Installs the IDT */
  void idt_install()
  {
      /* Sets the special IDT pointer up, just like in 'gdt.c' */
      idtp.limit = (sizeof (struct idt_entry) * 256) - 1;
      idtp.base =(int) &idt;
  
      /* Clear out the entire IDT, initializing it to zeros */
       memset((char *)&idt, 0, sizeof(struct idt_entry) * 256);
  
      /* Add any new ISRs to the IDT here using idt_set_gate */
  
      /* Points the processor's internal register to the new IDT */
      idt_load();
  }
  		
  
  