Initial commit

src/idt.c

@@ -0,0 +1,59 @@
+#include "../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 = &idt;
+
+    /* Clear out the entire IDT, initializing it to zeros */
+    memset(&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();
+}