CTAOS v3

SysCore/hal/idt/compile.bat

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+@echo off
+rem The name of the loader assembly file (without extension, must be .asm):
+set loader_name=loader
+
+rem NASM and DJGPP executable paths:
+set nasm_path=C:\nasm
+set djgpp_path=C:\DJGPP\bin
+set objpath=../../objects
+set incpath=../../include
+
+@echo on
+%nasm_path%\nasm.exe -f aout -o %objpath%/idt_asm.o idt.asm
+%djgpp_path%\gcc.exe -Wall -O -fstrength-reduce -fomit-frame-pointer -nostdinc -fno-builtin -I%incpath% -c -o %objpath%/idt.o idt.c 
+
+@echo off
+@echo .
+@echo Done!
+
+@pause

SysCore/hal/idt/idt.asm

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+bits 32
+
+; !!!  IDT  !!!
+; Loads the IDT defined in '_idtp'
+global _i86_idt_load
+extern _idtp
+_i86_idt_load:
+      lidt [_idtp]
+      ret

SysCore/hal/idt/idt.c

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+/******************************************************************
+ *    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();
+}

SysCore/hal/idt/idt.h

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+/******************************************************************
+ *    idt.h  -  INTERRUPT DESCRIPTOR TABLE                        *
+ *      Contains structures and function declarations for IDT     *
+ ******************************************************************/
+
+#ifndef __IDT_H
+#define __IDT_H
+
+/* Defines an IDT entry */
+struct idt_entry
+{
+    unsigned short base_lo;
+    unsigned short sel;
+    unsigned char always0;
+    unsigned char flags;
+    unsigned short base_hi;
+} __attribute__((packed));
+
+struct idt_ptr
+{
+    unsigned short limit;
+    unsigned int base;
+} __attribute__((packed));
+
+
+/* This exists in 'start.asm', and is used to load our IDT */
+extern void i86_idt_load();
+extern void i86_idt_set_gate(unsigned char num, unsigned long base, unsigned short sel, unsigned char flags);
+extern struct idt_entry* i86_idt_get_gate(unsigned char num);
+extern void i86_idt_install();
+
+#endif