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	/*
	*		idt.c
	*	x86 interrupt descriptor table definition and initialization.
	*	For WolfNet OS
	*	By John Wolfe 2015
	*/

/* LibC headers. */
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* LibK headers. */
#include <arch.h>
#include <kernelint.h>
#include <core/interrupts.h>
#include <drivers/virt_ic.h>

/*
*	Name		Bit	Full Name			Description
*	Offset		48..63	Offset 16..31			Higher part of the offset.
*	P		47	Present				Set to 0 for unused interrupts.
*	DPL		45,46	Descriptor Privilege Level	Gate call protection. Specifies the lowest privilege Level the caller can have. So hardware and CPU interrupts can be protected from being called out of userspace.
*	S		44	Storage Segment			Set to 0 for interrupt gates (see below).
*	Type		40..43	Gate Type 0..3			
*		IDT gate types:
*		0b0101		0x5	32 bit task gate
*		0b0110		0x6	16-bit interrupt gate
*		0b0111		0x7	16-bit trap gate
*		0b1110		0xE	32-bit interrupt gate
*		0b1111		0xF	32-bit trap gate
*	0		32..39	Unused 0..7			Have to be 0.
*	Selector	16..31	Selector 0..15			Selector of the interrupt function (to make sense - the kernel's selector). The selector's descriptor's DPL field has to be 0.
*	Offset		0..15	Offset 0..15			Lower part of the interrupt function's offset address (also known as pointer).
*/

static inline void idt_defineidtr(void*, kernel_uint16_t);

void idt_initialize(void)
{
	printf("Initializing IDT...\n");
	for (int i = 0; i < (IDT_ENTRIES - 1); ++i) {
		memset(&idt[i], '0', sizeof(idt_table_t));
	}
	#ifdef __debug_kernel
	printf("sizeof(idt): %u bytes.\n", (unsigned int) sizeof(idt));
	printf("sizeof idt_table_t: %u bytes.\n", (unsigned int) sizeof(idt_table_t));
	printf("idt_table_t.offset_1 offset: %u bytes.\n", (unsigned int) offsetof(idt_table_t, offset_1));
	printf("idt_table_t.selector offset: %u bytes.\n", (unsigned int) offsetof(idt_table_t, selector));
	printf("idt_table_t.zero offset: %u bytes.\n", (unsigned int) offsetof(idt_table_t, zero));
	printf("idt_table_t.type_attr offset: %u bytes.\n", (unsigned int) offsetof(idt_table_t, type_attr));
	printf("idt_table_t.offset_2 offset: %u bytes.\n", (unsigned int) offsetof(idt_table_t, offset_2));
	#endif
	idt_defineidtr(&idt, sizeof(idt));
	printf("IDT initialization complete!\n");
}

void idt_encode_entry(void* idt_entry, kernel_uint16_t selector, void* offset, kernel_uint8_t gate_type, kernel_uint8_t priv_level, kernel_uint8_t used_bit)
{
	idt_table_t* new_entry = (idt_table_t*) idt_entry;
	kernel_uint32_t pointer = (kernel_uint32_t) offset;
	new_entry->offset_1 = (kernel_uint16_t) pointer & 0xFFFF;
	new_entry->offset_2 = (kernel_uint16_t) pointer >> 16;
	new_entry->selector = selector;				/* NOTE: Minimum privilege for calling process. */
	new_entry->zero = 0; 						/* NOTE: THIS MUST NEVER BE CHANGED! */
	new_entry->type_attr = gate_type & 0x0F;
	new_entry->type_attr |= (priv_level & 0x03) << 5;
	if (used_bit == 1) {
		new_entry->type_attr |= 0x80;
	}
	else if (used_bit == 0) {
		new_entry->type_attr &= ~(0x80);
	}
	if (gate_type == 0xE || gate_type == 0x6) {
		new_entry->type_attr &= ~(0x10); 				/* NOTE: This is always set to zero for interrupt gates. */
	}
}

/* IDT definition function. */
static inline void idt_defineidtr(void* base, kernel_uint16_t size)
{
	typedef struct lidt_data {
		kernel_uint16_t length;
		kernel_uint32_t base;
	} __attribute__((packed)) lidt_data_t;
	lidt_data_t lidt_data;
	lidt_data.length = size;
	lidt_data.base = (kernel_uint32_t) base;
	if (offsetof(lidt_data_t, base) != 2) {
		printf("IDT Error: LIDT base offset = %u\n", (unsigned int) offsetof(lidt_data_t, base));
		kernel_exit();
	}
	#ifdef __debug_kernel
	printf("LIDT length offset = %u\n", (unsigned int) offsetof(lidt_data_t, length));
	printf("LIDT length base = %u\n", (unsigned int) offsetof(lidt_data_t, base));
	#endif
	__asm__ __volatile__ ("lidt (%0)"::"r"(&lidt_data));
}

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idt_encode_entry(idt+32, KERNEL_CODE_DESCRIPTOR, irq0handler, INTERRUPT_GATE, 0, 1);

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/* IDT. */
void idt_initialize(void);
void idt_encode_entry(void*, kernel_uint16_t, void *, kernel_uint8_t, kernel_uint8_t, kernel_uint8_t);

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idt_defineidtr(idt, sizeof(idt) - 1);

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int $0x80

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int $0x80