kernel/idt.c

   1 /*
   2  *  ZeX/OS
   3  *  Copyright (C) 2007  Tomas 'ZeXx86' Jedrzejek (zexx86@gmail.com)
   4  *
   5  *  This program is free software: you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation, either version 3 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  This program is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License
  16  *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17  */
  18
  19
  20 #include <system.h>
  21 #include <x86.h>
  22 #include <string.h>
  23
  24 /* Defines an IDT entry */
  25 struct idt_entry
  26 {
  27         unsigned short base_lo;
  28         unsigned short sel;
  29         unsigned char always0;
  30         unsigned char flags;
  31         unsigned short base_hi;
  32 } __attribute__((packed));
  33
  34 struct idt_ptr
  35 {
  36         unsigned short limit;
  37         unsigned int base;
  38 } __attribute__((packed));
  39
  40 /* Declare an IDT of 256 entries. Although we will only use the
  41 *  first 32 entries in this tutorial, the rest exists as a bit
  42 *  of a trap. If any undefined IDT entry is hit, it normally
  43 *  will cause an "Unhandled Interrupt" exception. Any descriptor
  44 *  for which the 'presence' bit is cleared (0) will generate an
  45 *  "Unhandled Interrupt" exception */
  46 struct idt_entry idt[256];
  47 struct idt_ptr idtp;
  48
  49 /* This exists in 'start.asm', and is used to load our IDT */
  50 extern void idt_load();
  51
  52 #define set_intr_gate(n,addr) \
  53         _set_gate(&idt[n],14,0,addr)
  54
  55 #define set_trap_gate(n,addr) \
  56         _set_gate(&idt[n],15,0,addr)
  57
  58 #define set_system_gate(n,addr) \
  59         _set_gate(&idt[n],15,3,addr)
  60
  61 /* Use this function to set an entry in the IDT. Alot simpler
  62 *  than twiddling with the GDT ;) */
  63 void idt_set_gate(unsigned char num, unsigned long base, unsigned short sel, unsigned char flags)
  64 {
  65         /* The interrupt routine's base address */
  66         idt[num].base_lo = (base & 0xFFFF);
  67         idt[num].base_hi = (base >> 16) & 0xFFFF;
  68
  69         /* The segment or 'selector' that this IDT entry will use
  70         *  is set here, along with any access flags */
  71         idt[num].sel = sel;
  72         idt[num].always0 = 0;
  73         idt[num].flags = flags;
  74 }
  75
  76 extern int system_call (void);
  77
  78 /* Installs the IDT */
  79 unsigned int idt_install ()
  80 {
  81         /* Sets the special IDT pointer up, just like in 'gdt.c' */
  82         idtp.limit = (sizeof (struct idt_entry) * 256) - 1;
  83         idtp.base = &idt;
  84
  85         /* Clear out the entire IDT, initializing it to zeros */
  86         memset(&idt, 0, sizeof(struct idt_entry) * 256);
  87
  88         /* Add any new ISRs to the IDT here using idt_set_gate */
  89
  90         /* Points the processor's internal register to the new IDT */
  91         idt_load ();
  92
  93         set_system_gate(0x80, &system_call);
  94
  95         return 1;
  96 }