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// descriptor_tables.c - Initialises the GDT and IDT, and defines the
// default ISR and IRQ handler.
// Based on code from Bran's kernel development tutorials.
// Rewritten for JamesM's kernel development tutorials.
#include "headers/common.h"
#include "headers/descriptor_tables.h"
#include "headers/isr.h"
#include <stdint.h>
// Lets us access our ASM functions from our C code.
extern void gdt_flush(uint32_t);
extern void idt_flush(uint32_t);
// Internal function prototypes.
static void init_gdt();
static void gdt_set_gate(int,uint32_t,uint32_t,uint8_t,uint8_t);
static void init_idt();
static void idt_set_gate(uint8_t,uint32_t,uint16_t,uint8_t);
gdt_entry_t gdt_entries[5];
gdt_ptr_t gdt_ptr;
idt_entry_t idt_entries[256];
idt_ptr_t idt_ptr;
// extern the isr handler array so it can nullified on start
extern isr_t interrupt_handlers[];
// Initialisation routine - zeroes all the interrupt service routines,
// initialises the GDT and IDT.
void init_descriptor_tables()
// Initialise the global descriptor table.
//nullify all the interrupt handlers
static void init_gdt()
gdt_ptr.limit = (sizeof(gdt_entry_t) * 5) - 1;
gdt_ptr.base = (uint32_t)&gdt_entries;
gdt_set_gate(0, 0, 0, 0, 0); // Null segment
gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF); // Code segment
gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF); // Data segment
gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF); // User mode code segment
gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF); // User mode data segment
// Set the value of one GDT entry.
static void gdt_set_gate(int num, uint32_t base,uint32_t limit, uint8_t access, uint8_t gran)
gdt_entries[num].base_low = (base & 0xFFFF);
gdt_entries[num].base_middle = (base >> 16) & 0xFF;
gdt_entries[num].base_high = (base >> 24) & 0xFF;
gdt_entries[num].limit_low = (limit & 0xFFFF);
gdt_entries[num].granularity = (limit >> 16) & 0x0F;
gdt_entries[num].granularity |= gran & 0xF0;
gdt_entries[num].access = access;
static void init_idt()
idt_ptr.limit = sizeof(idt_entry_t) * 256 -1;
idt_ptr.base = (uint32_t)&idt_entries;
memset(&idt_entries, 0, sizeof(idt_entry_t)*256);
// Remap the irq table.
outb(0x20, 0x11);
outb(0xA0, 0x11);
outb(0x21, 0x20);
outb(0xA1, 0x28);
outb(0x21, 0x04);
outb(0xA1, 0x02);
outb(0x21, 0x01);
outb(0xA1, 0x01);
outb(0x21, 0x0);
outb(0xA1, 0x0);
idt_set_gate( 0, (uint32_t)isr0 , 0x08, 0x8E);
idt_set_gate( 1, (uint32_t)isr1 , 0x08, 0x8E);
idt_set_gate( 2, (uint32_t)isr2 , 0x08, 0x8E);
idt_set_gate( 3, (uint32_t)isr3 , 0x08, 0x8E);
idt_set_gate( 4, (uint32_t)isr4 , 0x08, 0x8E);
idt_set_gate( 5, (uint32_t)isr5 , 0x08, 0x8E);
idt_set_gate( 6, (uint32_t)isr6 , 0x08, 0x8E);
idt_set_gate( 7, (uint32_t)isr7 , 0x08, 0x8E);
idt_set_gate( 8, (uint32_t)isr8 , 0x08, 0x8E);
idt_set_gate( 9, (uint32_t)isr9 , 0x08, 0x8E);
idt_set_gate(10, (uint32_t)isr10, 0x08, 0x8E);
idt_set_gate(11, (uint32_t)isr11, 0x08, 0x8E);
idt_set_gate(12, (uint32_t)isr12, 0x08, 0x8E);
idt_set_gate(13, (uint32_t)isr13, 0x08, 0x8E);
idt_set_gate(14, (uint32_t)isr14, 0x08, 0x8E);
idt_set_gate(15, (uint32_t)isr15, 0x08, 0x8E);
idt_set_gate(16, (uint32_t)isr16, 0x08, 0x8E);
idt_set_gate(17, (uint32_t)isr17, 0x08, 0x8E);
idt_set_gate(18, (uint32_t)isr18, 0x08, 0x8E);
idt_set_gate(19, (uint32_t)isr19, 0x08, 0x8E);
idt_set_gate(20, (uint32_t)isr20, 0x08, 0x8E);
idt_set_gate(21, (uint32_t)isr21, 0x08, 0x8E);
idt_set_gate(22, (uint32_t)isr22, 0x08, 0x8E);
idt_set_gate(23, (uint32_t)isr23, 0x08, 0x8E);
idt_set_gate(24, (uint32_t)isr24, 0x08, 0x8E);
idt_set_gate(25, (uint32_t)isr25, 0x08, 0x8E);
idt_set_gate(26, (uint32_t)isr26, 0x08, 0x8E);
idt_set_gate(27, (uint32_t)isr27, 0x08, 0x8E);
idt_set_gate(28, (uint32_t)isr28, 0x08, 0x8E);
idt_set_gate(29, (uint32_t)isr29, 0x08, 0x8E);
idt_set_gate(30, (uint32_t)isr30, 0x08, 0x8E);
idt_set_gate(31, (uint32_t)isr31, 0x08, 0x8E);
static void idt_set_gate(uint8_t num, uint32_t base, uint16_t sel, uint8_t flags)
idt_entries[num].base_lo = base & 0xFFFF;
idt_entries[num].base_hi = (base >> 16) & 0xFFFF;
idt_entries[num].sel = sel;
idt_entries[num].always0 = 0;
// We must uncomment the OR below when we get to using user-mode.
// It sets the interrupt gate's privilege level to 3.
idt_entries[num].flags = flags /* | 0x60 */;