From f81bf65484fa8c81a1886f456c71f1e6eebe84e9 Mon Sep 17 00:00:00 2001
From: Alexis211 <alexis211@gmail.com>
Date: Tue, 10 Aug 2010 20:39:57 +0200
Subject: Added a lot of comments in kernel code. A bit of cleaning too.

---
 src/kernel/core/kmain.c   | 12 +++++++++--
 src/kernel/core/monitor.c | 27 ++++++++++++-----------
 src/kernel/core/monitor.h |  5 +++++
 src/kernel/core/sys.c     | 21 ++++++++++++++----
 src/kernel/core/sys.h     | 10 +++++----
 src/kernel/ipc/shm.c      | 16 ++++++++++++++
 src/kernel/ipc/shm.h      |  5 -----
 src/kernel/lib/mutex.c    |  1 +
 src/kernel/mem/gdt.c      | 18 ++++++++++------
 src/kernel/mem/gdt.h      |  9 ++++++++
 src/kernel/mem/heap.c     |  7 ++++++
 src/kernel/mem/heap.h     |  5 +++++
 src/kernel/mem/mem.c      |  4 ++++
 src/kernel/mem/mem.h      |  3 +++
 src/kernel/mem/paging.c   | 27 ++++++++++++++++++++++-
 src/kernel/mem/seg.c      | 20 ++++++++++++++++-
 src/kernel/mem/seg.h      | 13 +++++------
 src/kernel/task/idt.c     | 14 +++++++++---
 src/kernel/task/idt.h     |  6 ++++++
 src/kernel/task/syscall.c |  2 +-
 src/kernel/task/syscall.h |  2 ++
 src/kernel/task/task.c    | 55 ++++++++++++++++++++++++++++++++++++-----------
 src/kernel/task/task.h    |  7 +++---
 src/kernel/task/timer.c   |  5 +++++
 24 files changed, 232 insertions(+), 62 deletions(-)

(limited to 'src')

diff --git a/src/kernel/core/kmain.c b/src/kernel/core/kmain.c
index d8f059a..cfb9935 100644
--- a/src/kernel/core/kmain.c
+++ b/src/kernel/core/kmain.c
@@ -10,7 +10,16 @@
 #include <mem/mem.h>
 #include <linker/elf.h>
 
+/*	The kernel's main procedure. This function is called in loader_.asm.
+	This function calls the initializer functions for all system parts.
+	It then loads the modules the kernel was given by the bootloader. 
+	This function never returns : once multitasking is started for good,
+	the execution flow of this function is never returned to. */
 void kmain(struct multiboot_info_t* mbd, int32_t magic) {
+	monitor_clear();
+
+	ASSERT(magic == MULTIBOOT_BOOTLOADER_MAGIC);
+
 	size_t totalRam = 0;
 	uint32_t i;
 
@@ -25,8 +34,6 @@ void kmain(struct multiboot_info_t* mbd, int32_t magic) {
 			mem_placementAddr = (mods[i].mod_end & 0xFFFFF000) + 0x1000;
 	}
 
-	monitor_clear();
-
 	if (magic != MULTIBOOT_BOOTLOADER_MAGIC) {
 		PANIC("wrong multiboot magic number.");
 	}
@@ -62,4 +69,5 @@ void kmain(struct multiboot_info_t* mbd, int32_t magic) {
 	monitor_write("Modules now RULE THE WORLD !\n");
 	sti();
 	tasking_switch();
+	PANIC("Should never happen. Something probably went wrong with multitasking.");
 }
diff --git a/src/kernel/core/monitor.c b/src/kernel/core/monitor.c
index 6660fe0..0d0f5eb 100644
--- a/src/kernel/core/monitor.c
+++ b/src/kernel/core/monitor.c
@@ -4,6 +4,9 @@
 static int cursor_x = 0, cursor_y = 0;
 static uint16_t *video_memory = (uint16_t*)0xE00B8000;
 
+static uint8_t attribute = 0x07; // 0 = background = black, 7 = foreground = white
+
+/*	For internal use only. Tells hardware to move the cursor at (cursor_x, cursor_y). */
 static void move_cursor() {
 	uint16_t cursor_location = cursor_y * 80 + cursor_x;
 	outb(0x3D4, 14);	//Sending high cursor byte
@@ -12,9 +15,9 @@ static void move_cursor() {
 	outb(0x3D5, cursor_location);
 }
 
+/*	For internal use only. Scrolls everything up one line. */
 static void scroll() {
-	uint8_t attribute_byte = (0 /* black */ << 4) | (7/* white */ & 0x0F);
-	uint16_t blank = (attribute_byte << 8) | 0x20;
+	uint16_t blank = (attribute << 8) | 0x20;
 
 	if (cursor_y >= 25) {
 		int i;
@@ -28,16 +31,11 @@ static void scroll() {
 	}
 }
 
+/*	Put one character on the screen. This function handles special characters \b, \t, \r and  \n. */
 void monitor_put(char c) {
-	uint8_t fg = 7;	//White
-	uint8_t bg = 0; //Black
-
-	uint16_t attribute = (fg & 0x0F) | (bg << 4);
-	attribute = attribute << 8;
-
-	if (c == 0x08 && cursor_x) {	//Backspace
+	if (c == '\b' && cursor_x) {	//Backspace
 		cursor_x--;
-	} else if (c == 0x09) {	//Tab
+	} else if (c == '\t') {	//Tab
 		cursor_x = (cursor_x + 8) & ~(8 - 1);
 	} else if (c == '\r') {	//Carriage return
 		cursor_x = 0;
@@ -45,7 +43,7 @@ void monitor_put(char c) {
 		cursor_x = 0;
 		cursor_y++;
 	} else if (c >= ' ') {	//Any printable character
-		video_memory[cursor_y * 80 + cursor_x] = c | attribute;
+		video_memory[cursor_y * 80 + cursor_x] = c | (attribute << 8);
 		cursor_x++;
 	}
 	if (cursor_x >= 80) {
@@ -57,9 +55,9 @@ void monitor_put(char c) {
 	move_cursor();
 }
 
+/* Clears the screen and moves cursor to (0,0) (top left corner) */
 void monitor_clear() {
-	uint8_t attribute_byte = (0 /* black */ << 4) | (15 /* white */ & 0x0F);
-	uint16_t blank = (attribute_byte << 8) | 0x20;
+	uint16_t blank = (attribute << 8) | 0x20;
 
 	int i;
 
@@ -71,12 +69,14 @@ void monitor_clear() {
 	move_cursor();
 }
 
+/* Writes a string to the monitor */
 void monitor_write(char *s) {
 	while (*s) {
 		monitor_put(*(s++));
 	}
 }
 
+/* Writes a number in hexadecimal notation to the monitor */
 void monitor_writeHex(uint32_t v) {
 	int i;
 
@@ -89,6 +89,7 @@ void monitor_writeHex(uint32_t v) {
 	}
 }
 
+/* Writes a number in decimal notation to the monitor */
 void monitor_writeDec(uint32_t v) {
 	if (v == 0) {
 		monitor_put('0');
diff --git a/src/kernel/core/monitor.h b/src/kernel/core/monitor.h
index f4605cf..c04632e 100644
--- a/src/kernel/core/monitor.h
+++ b/src/kernel/core/monitor.h
@@ -10,6 +10,11 @@ void monitor_writeHex(uint32_t v);
 void monitor_writeDec(uint32_t v);
 
 #define NL monitor_put('\n');
+#define WHERE { monitor_write("(kernel:");	\
+				monitor_write(__FILE__);	\
+				monitor_write(":");			\
+				monitor_writeDec(__LINE__);	\
+				monitor_write(") "); }
 
 #endif
 
diff --git a/src/kernel/core/sys.c b/src/kernel/core/sys.c
index 1e07f7c..96d4908 100644
--- a/src/kernel/core/sys.c
+++ b/src/kernel/core/sys.c
@@ -1,6 +1,9 @@
 #include "sys.h"
 #include "monitor.h"
 
+/*	These four functions are wrappers around ASM operations.
+	These functions are used when comunicating with the system hardware. */
+
 void outb(uint16_t port, uint8_t value) {
 	asm volatile("outb %1, %0" : : "dN"(port), "a"(value));
 }
@@ -21,14 +24,24 @@ uint16_t inw(uint16_t port) {
 	return ret;
 }
 
+/*	These two functions stop the system, reporting an error message, because something bad happenned. */
+
 void panic(char* message, char* file, int line) {
-	monitor_write("\n>> PANIC: >>");
-	monitor_write(message); monitor_write("<< at "); monitor_write(file);
-	monitor_write(":"); monitor_writeDec(line);
-	monitor_write("\nSystem halted -_-'");
+	monitor_write("\n\nPANIC:\t\t"); monitor_write(message);
+	monitor_write("\n File:\t\t"); monitor_write(file); monitor_put(':'); monitor_writeDec(line);
+	monitor_write("\n\t\tSystem halted -_-'\n");
+	asm volatile("cli; hlt");
+}
+
+void panic_assert(char* assertion, char* file, int line) {
+	monitor_write("\n\nASSERT FAILED:\t"); monitor_write(assertion);
+	monitor_write("\n File:\t\t"); monitor_write(file); monitor_put(':'); monitor_writeDec(line);
+	monitor_write("\n\t\tSystem halted -_-'\n");
 	asm volatile("cli; hlt");
 }
 
+/* Global system mutex. See comments in sys.h. */
+
 static uint32_t if_locks = 1;
 
 void cli() {
diff --git a/src/kernel/core/sys.h b/src/kernel/core/sys.h
index 2f8cd5e..f147922 100644
--- a/src/kernel/core/sys.h
+++ b/src/kernel/core/sys.h
@@ -9,11 +9,13 @@ uint8_t inb(uint16_t port);
 uint16_t inw(uint16_t port);
 
 #define PANIC(s) panic(s, __FILE__, __LINE__);
+#define ASSERT(s) { if (!(s)) panic_assert(#s, __FILE__, __LINE__); }
 void panic(char* message, char* file, int line);
+void panic_assert(char* assertion, char* file, int line);
 
-void sti();		//GLOBAL SYSTEM MUTEX
-void cli();
-
-#define WHERE { monitor_write("(kernel:"); monitor_write(__FILE__); monitor_write(":"); monitor_writeDec(__LINE__); monitor_write(") "); }
+/*	For some actions, we use cli and sti as a global system mutex.
+	These actions include : system initialization, process creation, interrupt handling. */
+void cli();	//lock
+void sti();	//unlock
 
 #endif
diff --git a/src/kernel/ipc/shm.c b/src/kernel/ipc/shm.c
index e760a0f..6e48613 100644
--- a/src/kernel/ipc/shm.c
+++ b/src/kernel/ipc/shm.c
@@ -4,6 +4,13 @@
 #include <task/task.h>
 #include <core/sys.h>
 
+static struct segment_map* shmseg_map(struct segment* seg, struct page_directory *pagedir, size_t offset);
+static void shmseg_unmap(struct segment_map*);
+static void shmseg_delete(struct segment *seg);
+static int shmseg_handleFault(struct segment_map *map, size_t addr, int write);
+
+/*	Call this function when creating a new shared memory segment.
+	Creates the shmseg struct and segment struct, fills them in. */
 struct segment* shmseg_make(size_t len, struct process* owner) {
 	struct shmseg *ss = kmalloc(sizeof(struct shmseg));
 	struct segment *se = kmalloc(sizeof(struct segment));
@@ -21,6 +28,8 @@ struct segment* shmseg_make(size_t len, struct process* owner) {
 	return se;
 }
 
+/*	For internal use only. Called when the shared memory is mapped somewhere.
+	Creates the segment_map struct and fills it up. */
 struct segment_map *shmseg_map(struct segment *seg, struct page_directory *pagedir, size_t offset) {
 	struct segment_map *sm = kmalloc(sizeof(struct segment_map));
 	sm->start = offset;
@@ -28,6 +37,8 @@ struct segment_map *shmseg_map(struct segment *seg, struct page_directory *paged
 	return sm;
 }
 
+/*	For internal use only. Called when the shared memory is unmapped from somewhere.
+	Unmaps all the pages from that place. */
 void shmseg_unmap(struct segment_map *sm) {
 	size_t i;
 	for (i = 0; i < sm->len; i += 0x1000) {
@@ -36,6 +47,8 @@ void shmseg_unmap(struct segment_map *sm) {
 	}
 }
 
+/*	For internal use only. Called when a page fault occurs.
+	Maps a page at that place, possibly requesting a free frame first. */
 int shmseg_handleFault(struct segment_map *sm, size_t addr, int write) {
 	struct shmseg *ss = sm->seg->seg_data;
 	addr &= 0xFFFFF000;
@@ -49,6 +62,8 @@ int shmseg_handleFault(struct segment_map *sm, size_t addr, int write) {
 	return 0;
 }
 
+/*	For internal use only. Called when the shared memory is deleted.
+	Frees all the frames. */
 void shmseg_delete(struct segment *seg) {
 	struct shmseg *ss = seg->seg_data;
 	unsigned i;
@@ -58,6 +73,7 @@ void shmseg_delete(struct segment *seg) {
 	kfree(ss->frames);
 }
 
+/*	Looks through the mapped segment for a process, looking for a shared memory segment at given offset. */
 struct segment_map* shmseg_getByOff(struct process* pr, size_t offset) {
 	struct segment_map* m = pr->pagedir->mappedSegs;
 	while (m != 0) {
diff --git a/src/kernel/ipc/shm.h b/src/kernel/ipc/shm.h
index 895a619..5459dbb 100644
--- a/src/kernel/ipc/shm.h
+++ b/src/kernel/ipc/shm.h
@@ -11,11 +11,6 @@ struct shmseg {
 
 //Shared memory segment stuff
 struct segment* shmseg_make(size_t len, struct process* owner);
-struct segment_map* shmseg_map(struct segment* seg, struct page_directory *pagedir, size_t offset);
-void shmseg_unmap(struct segment_map*);
-void shmseg_delete(struct segment *seg);
-int shmseg_handleFault(struct segment_map *map, size_t addr, int write);
-
 		//find a shared memory segment in current address space by its offset
 struct segment_map* shmseg_getByOff(struct process* pr, size_t offset);	
 
diff --git a/src/kernel/lib/mutex.c b/src/kernel/lib/mutex.c
index f3ed11f..2664eb0 100644
--- a/src/kernel/lib/mutex.c
+++ b/src/kernel/lib/mutex.c
@@ -1,6 +1,7 @@
 #include "mutex.h"
 #include <task/task.h>
 
+/*	Internal use only. This function is atomic, meaning it cannot be interrupted by a system task switch. */
 static uint32_t atomic_exchange(uint32_t* ptr, uint32_t newval) {
 	uint32_t r;
 	asm volatile("xchg (%%ecx), %%eax" : "=a"(r) : "c"(ptr), "a"(newval));
diff --git a/src/kernel/mem/gdt.c b/src/kernel/mem/gdt.c
index e9a1be5..8ee403a 100644
--- a/src/kernel/mem/gdt.c
+++ b/src/kernel/mem/gdt.c
@@ -2,19 +2,23 @@
 #include <stdlib.h>
 #include <core/monitor.h>
 
-extern void gdt_flush(uint32_t);	//ASM (idt_.asm)
+extern void gdt_flush(uint32_t);	//ASM (imported from idt_.asm)
 extern void tss_flush();
 
-#define GDT_ENTRIES 6
+#define GDT_ENTRIES 6	// The contents of each entry is defined in gdt_init.
 
 static struct tss_entry tss_entry;
 static struct gdt_entry gdt_entries[GDT_ENTRIES];
 static struct gdt_ptr gdt_ptr;
 
+/*	This function is called by the task_switch function on each context switch.
+	It updates the TSS so that an interrupt will be handled on the correct kernel stack
+	(one kernel stack is allocated to each thread). */
 void gdt_setKernelStack(uint32_t esp0) {
 	tss_entry.esp0 = esp0;
 }
 
+/*	For internal use only. Writes one entry of the GDT with given parameters. */
 static void gdt_setGate(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;
@@ -26,6 +30,7 @@ static void gdt_setGate(int num, uint32_t base, uint32_t limit, uint8_t access,
 	gdt_entries[num].access = access;
 }
 
+/*	For internal use only. Writes one entry of the GDT, that entry being a pointer to the TSS. */
 static void gdt_writeTss(int num, uint32_t ss0, uint32_t esp0) {
 	uint32_t base = (uint32_t)&tss_entry;
 	uint32_t limit = base + sizeof(struct tss_entry);
@@ -40,15 +45,16 @@ static void gdt_writeTss(int num, uint32_t ss0, uint32_t esp0) {
 	tss_entry.ss = tss_entry.ds = tss_entry.es = tss_entry.fs = tss_entry.gs = 0x13;
 }
 
+/*	Write data to the GDT and enable it. */
 void gdt_init() {
 	gdt_ptr.limit = (sizeof(struct gdt_entry) * GDT_ENTRIES) - 1;
 	gdt_ptr.base = (uint32_t)&gdt_entries;
 
 	gdt_setGate(0, 0, 0, 0, 0);					//Null segment
-	gdt_setGate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);	//Kernel code segment
-	gdt_setGate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);	//Kernel data segment
-	gdt_setGate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);	//User code segment
-	gdt_setGate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);	//User data segment
+	gdt_setGate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);	//Kernel code segment	0x08
+	gdt_setGate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);	//Kernel data segment	0x10
+	gdt_setGate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);	//User code segment		0x18
+	gdt_setGate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);	//User data segment		0x20
 	gdt_writeTss(5, 0x10, 0);
 
 	gdt_flush((uint32_t)&gdt_ptr);
diff --git a/src/kernel/mem/gdt.h b/src/kernel/mem/gdt.h
index 485002b..1b33dac 100644
--- a/src/kernel/mem/gdt.h
+++ b/src/kernel/mem/gdt.h
@@ -3,6 +3,11 @@
 
 #include <types.h>
 
+/*	The GDT is one of the x86's descriptor tables. It is used for memory segmentation.
+	Here, we don't use segmentation to separate processes from one another (this is done with paging).
+	We only use segmentation to make the difference between kernel mode (ring 3) and user mode (ring 0) */
+
+/* 	One entry of the table */
 struct gdt_entry {
 	uint16_t limit_low;
 	uint16_t base_low;
@@ -12,11 +17,15 @@ struct gdt_entry {
 	uint8_t base_high;
 } __attribute__((packed));
 
+/*	Structure defining the whole table : address and size (in bytes). */
 struct gdt_ptr {
 	uint16_t limit;
 	uint32_t base;
 } __attribute__((packed));
 
+/*	The TSS is used for hardware multitasking.
+	We don't use that, but we still need a TSS so that user mode process exceptions
+	can be handled correctly by the kernel.	*/
 struct tss_entry {
 	uint32_t prev_tss;   // The previous TSS - if we used hardware task switching this would form a linked list.
 	uint32_t esp0;       // The stack pointer to load when we change to kernel mode.
diff --git a/src/kernel/mem/heap.c b/src/kernel/mem/heap.c
index b6d2cd4..b7f6c97 100644
--- a/src/kernel/mem/heap.c
+++ b/src/kernel/mem/heap.c
@@ -6,6 +6,7 @@
 
 /* *******************			HEADER    	   ****************** */
 
+/*	For internal use only. Inserts a hole in the heap's hole index at the correct position. */
 static void heapIdx_insert(struct heap *heap, struct heap_header *e) {
 	if ((heap->idxused + sizeof(struct heap_header*) + (size_t)heap->idx) >= heap->start_addr) return;
 
@@ -28,6 +29,7 @@ static void heapIdx_insert(struct heap *heap, struct heap_header *e) {
 	}
 }
 
+/* For internal use only. Removes a hole from the heap's hole index. */
 static void heapIdx_remove(struct heap *heap, struct heap_header *e) {
 	uint32_t iterator;
 	for (iterator = 0; iterator < heap->idxused; iterator++) {
@@ -43,6 +45,7 @@ static void heapIdx_remove(struct heap *heap, struct heap_header *e) {
 
 /* ********************			CONTENTS		********************* */
 
+/*	Initializes the heap, creates the correct data structures. */
 void heap_create(struct heap *heap, size_t start, size_t idxsize, size_t datasize, size_t maxdatasize) {
 	uint32_t i;
 
@@ -71,6 +74,7 @@ void heap_create(struct heap *heap, size_t start, size_t idxsize, size_t datasiz
 	heapIdx_insert(heap, hole);
 }
 
+/*	For internal use only. Called by heap_alloc when necessary. Expands the heap to take more space. */
 static uint32_t heap_expand(struct heap *heap, size_t quantity) {
 	uint32_t i;
 
@@ -116,6 +120,7 @@ static uint32_t heap_expand(struct heap *heap, size_t quantity) {
 	return 1;
 }
 
+/*	For internal use only. Called by heap_free when necessary. Reduces the heap's size. */
 static void heap_contract(struct heap *heap) {
 	struct heap_footer *last_footer = (struct heap_footer*)(heap->end_addr - sizeof(struct heap_footer));
 	struct heap_header *last_header = last_footer->header;
@@ -142,6 +147,7 @@ static void heap_contract(struct heap *heap) {
 	}
 }
 
+/*	Alocate some bytes on the heap. */
 void* heap_alloc(struct heap *heap, size_t sz) {
 	size_t newsize = sz + sizeof(struct heap_header) + sizeof(struct heap_footer);
 	uint32_t iterator = 0;
@@ -185,6 +191,7 @@ void* heap_alloc(struct heap *heap, size_t sz) {
 	return (void*)((size_t)loc + sizeof(struct heap_header));
 }
 
+/*	Frees a block previously allocated on the heap. */
 void heap_free(struct heap *heap, void* ptr) {
 	if (ptr == 0) return;
 	if ((size_t)ptr < heap->start_addr || (size_t)ptr > heap->end_addr) return;
diff --git a/src/kernel/mem/heap.h b/src/kernel/mem/heap.h
index 39ba37e..8f8cdcf 100644
--- a/src/kernel/mem/heap.h
+++ b/src/kernel/mem/heap.h
@@ -1,6 +1,11 @@
 #ifndef DEF_HEAP_H
 #define DEF_HEAP_H
 
+/*	The heap is the data structure that permits allocating and freeing memory easily.
+	The functions in this file are only used by mem.c, which provides kmalloc and kfree.
+	The heap algorithm used is the one described here : 
+	http://www.jamesmolloy.co.uk/tutorial_html/7.-The%20Heap.html */
+
 #include "types.h"
 
 struct heap_header {
diff --git a/src/kernel/mem/mem.c b/src/kernel/mem/mem.c
index 06242a5..47a03dc 100644
--- a/src/kernel/mem/mem.c
+++ b/src/kernel/mem/mem.c
@@ -22,6 +22,7 @@ static struct freepage {
 } freepages[FREEPAGESTOKEEP];
 uint32_t freepagecount = 0;
 
+/*	For internal use only. Populates the cache of pages that can be given to requesters. */
 static void get_free_pages() {
 	static uint32_t locked = 0;
 	uint32_t i;
@@ -49,6 +50,7 @@ static void get_free_pages() {
 	locked = 0;
 }
 
+/*	Gives one page from the cache to someone requesting it. */
 void* kmalloc_page(size_t *phys) {
 	cli();
 	get_free_pages();
@@ -72,12 +74,14 @@ void kfree_page(void* ptr) {
 
 static struct heap kheap;
 
+/*	Called on kernel start. Creates the kernel heap. */
 void kheap_init() {
 	heap_create(&kheap, (mem_placementAddr & 0xFFFFF000) + 0x1000, KHEAP_IDXSIZE, KHEAP_INITSIZE, KHEAP_MAXSIZE);
 	kheap_working = 1;
 	monitor_write("[KHeap] ");
 }
 
+/*	Allocates on the heap if possible. If not possible, allocates just after the kernel code. */
 void* kmalloc(size_t size) {
 	if (kheap_working) {
 		return heap_alloc(&kheap, size);
diff --git a/src/kernel/mem/mem.h b/src/kernel/mem/mem.h
index 5417d5f..b372fae 100644
--- a/src/kernel/mem/mem.h
+++ b/src/kernel/mem/mem.h
@@ -1,6 +1,9 @@
 #ifndef DEF_MEM_H
 #define DEF_MEM_H
 
+/*	mem.c provides the kernel's allocation and freeing functions.
+	kmalloc_page and kfree_page are used mostly for paging. */
+
 #include <types.h>
 
 void* kmalloc_page(size_t *phys);
diff --git a/src/kernel/mem/paging.c b/src/kernel/mem/paging.c
index 4992d5e..f8f69f1 100644
--- a/src/kernel/mem/paging.c
+++ b/src/kernel/mem/paging.c
@@ -11,7 +11,9 @@ static struct bitset frames;
 
 struct page_directory *kernel_pagedir, *current_pagedir;
 
-/* ACCESSOR FUNCTIONS FOR STATIC BITSET */
+/**************************		PHYSICAL MEMORY ALLOCATION	************************/
+
+/*	Allocates a page of physical memory. */
 uint32_t frame_alloc() {
 	uint32_t free = bitset_firstFree(&frames);
 	bitset_set(&frames, free);
@@ -22,6 +24,13 @@ void frame_free(uint32_t id) {
 	bitset_clear(&frames, id);
 }
 
+/*************************		PAGING INITIALIZATION		*****************************/
+
+/*	This function creates the kernel page directory. It must be called before the GDT is loaded.
+	It maps 0xE0000000+ to the corresponding physical kernel code, but it also maps
+	0x00000000+ to that code because with the false GDT we set up in loader_.asm,
+	the code will be looked for at the beginning of the memory. Only when the real GDT is loaded
+	we can de-allocate pages at 0x00000000 ; this is done by paging_cleanup. */
 void paging_init(size_t totalRam) {
 	uint32_t i;
 
@@ -50,6 +59,7 @@ void paging_init(size_t totalRam) {
 	monitor_write("} [Paging] ");
 }
 
+/*	De-allocates pages at 0x00000000 where kernel code was read from with the GDT from loader_.asm. */
 void paging_cleanup() {
 	uint32_t i;
 	for (i = 0; i < (mem_placementAddr - 0xE0000000) / 0x100000; i++) {
@@ -59,6 +69,10 @@ void paging_cleanup() {
 	monitor_write("[PD Cleanup] ");
 }
 
+/*************************		PAGING EVERYDAY USE		*****************************/
+
+/*	Switch to a page directory. Can be done if we are sure not to be interrupted by a task switch.
+	Example use for cross-memory space writing in linker/elf.c */
 void pagedir_switch(struct page_directory *pd) {
 	current_pagedir = pd;
 	asm volatile("mov %0, %%cr3" : : "r"(pd->physicalAddr));
@@ -68,6 +82,7 @@ void pagedir_switch(struct page_directory *pd) {
 	asm volatile("mov %0, %%cr0" : : "r"(cr0));
 }
 
+/*	Creates a new page directory for a process, and maps the kernel page tables on it. */
 struct page_directory *pagedir_new() {
 	uint32_t i;
 
@@ -87,6 +102,7 @@ struct page_directory *pagedir_new() {
 	return pd;
 }
 
+/*	Deletes a page directory, cleaning it up. */
 void pagedir_delete(struct page_directory *pd) {
 	uint32_t i;
 	//Unmap segments
@@ -99,6 +115,9 @@ void pagedir_delete(struct page_directory *pd) {
 	kfree(pd);
 }
 
+/*	Handle a paging fault. First, looks for the corresponding segment.
+	If the segment was found and it handles the fault, return normally.
+	Else, display informatinos and return an error. */
 uint32_t paging_fault(struct registers *regs) {
 	size_t addr;
 	struct segment_map *seg = 0;
@@ -127,6 +146,9 @@ uint32_t paging_fault(struct registers *regs) {
 	return 0;
 }
 
+/*	Gets the corresponding page in a page directory for a given address.
+	If make is set, the necessary page table can be created.
+	Can return 0 if make is not set. */
 struct page *pagedir_getPage(struct page_directory *pd, uint32_t address, int make) {
 	address /= 0x1000;
 	uint32_t table_idx = address / 1024;
@@ -145,6 +167,7 @@ struct page *pagedir_getPage(struct page_directory *pd, uint32_t address, int ma
 	}
 }
 
+/*	Modifies a page structure so that it is mapped to a frame. */
 void page_map(struct page *page, uint32_t frame, uint32_t user, uint32_t rw) {
 	if (page != 0 && page->frame == 0 && page->present == 0) {
 		page->present = 1;
@@ -154,6 +177,7 @@ void page_map(struct page *page, uint32_t frame, uint32_t user, uint32_t rw) {
 	}
 }
 
+/*	Modifies a page structure so that it is no longer mapped to a frame. */
 void page_unmap(struct page *page) {
 	if (page != 0) {
 		page->frame = 0;
@@ -161,6 +185,7 @@ void page_unmap(struct page *page) {
 	}
 }
 
+/*	Same as above but also frees the frame. */
 void page_unmapFree(struct page *page) {
 	if (page != 0) {
 		if (page->frame != 0) frame_free(page->frame);
diff --git a/src/kernel/mem/seg.c b/src/kernel/mem/seg.c
index e3eca67..4a33db3 100644
--- a/src/kernel/mem/seg.c
+++ b/src/kernel/mem/seg.c
@@ -2,6 +2,8 @@
 #include "mem.h"
 #include <core/sys.h>
 
+/*	Call this function when mapping a segment to a page directory.
+	Calls the appropriate map method and updates the segment's and pagedir's information. */
 struct segment_map *seg_map(struct segment* seg, struct page_directory *pagedir, size_t offset) {
 	struct segment_map *sm = seg->map(seg, pagedir, offset);
 	if (sm == 0) return 0;
@@ -13,6 +15,9 @@ struct segment_map *seg_map(struct segment* seg, struct page_directory *pagedir,
 	return sm;
 }
 
+/*	Call this function when unmapping a segment from a page directory.
+	The segment will automatically be deleted if it is not mapped.
+	Calls the appropriate unmap method and updates the segment's and pagedir's information. */
 void seg_unmap(struct segment_map *map) {
 	map->seg->unmap(map);
 	if (map->pagedir->mappedSegs == map) {
@@ -32,7 +37,14 @@ void seg_unmap(struct segment_map *map) {
 }
 
 // ************************************   SIMPLESEG stuff *************
+ 
+static struct segment_map* simpleseg_map(struct segment* seg, struct page_directory* pagedir, size_t offset);
+static void simpleseg_unmap(struct segment_map*);
+static void simpleseg_delete(struct segment *seg);
+static int simpleseg_handleFault(struct segment_map* map, size_t addr, int write);
 
+/*	Call this when creating a simpleseg.
+	Creates the simpleseg structure and the segment structure and fills them up. */
 struct segment* simpleseg_make(size_t start, size_t len, int writable) {
 	struct simpleseg *ss = kmalloc(sizeof(struct simpleseg));
 	struct segment *se = kmalloc(sizeof(struct segment));
@@ -46,6 +58,7 @@ struct segment* simpleseg_make(size_t start, size_t len, int writable) {
 	return se;
 }
 
+/*	For internal use only. Called when a simpleseg is mapped to a pagedirectory. */
 struct segment_map* simpleseg_map(struct segment* seg, struct page_directory* pagedir, size_t offset) {
 	struct segment_map *sm = kmalloc(sizeof(struct segment_map));
 	sm->start = ((struct simpleseg*)(seg->seg_data))->start;
@@ -53,6 +66,8 @@ struct segment_map* simpleseg_map(struct segment* seg, struct page_directory* pa
 	return sm;
 }
 
+/*	For internal use only. Called when a simpleseg is unmapped.
+	Frees all the allocated pages. */
 void simpleseg_unmap(struct segment_map* sm) {
 	size_t i;
 	for (i = sm->start; i < sm->start + sm->len; i += 0x1000) {
@@ -60,6 +75,7 @@ void simpleseg_unmap(struct segment_map* sm) {
 	}
 }
 
+/*	For internal use only. Handles a page fault. Can allocate and map a frame if necessary. */
 int simpleseg_handleFault(struct segment_map* sm, size_t addr, int write) {
 	struct simpleseg *ss = sm->seg->seg_data;
 	if (write && !ss->writable) return 1;
@@ -70,14 +86,16 @@ int simpleseg_handleFault(struct segment_map* sm, size_t addr, int write) {
 	return 0;
 }
 
+/*	For internal use only. Called when the simpleseg is deleted. Does nothing. */
 void simpleseg_delete(struct segment* seg) {
 }
 
+/*	Call this to resize a simpleseg. Ajusts the size and frees pages if the new size is smaller.*/
 int simpleseg_resize(struct segment_map *map, size_t len) {
 	size_t i;
 
 	if (map == 0) return -1;
-	if (map->seg->delete != simpleseg_delete) return -2;
+	if (map->seg->delete != simpleseg_delete) return -2;	//check segment is a simpleseg
 
 	struct simpleseg *s = (struct simpleseg*)map->seg->seg_data;
 	if (len & 0xFFF) len = (len & 0xFFFFF000) + 0x1000;
diff --git a/src/kernel/mem/seg.h b/src/kernel/mem/seg.h
index 26664dc..d37ba59 100644
--- a/src/kernel/mem/seg.h
+++ b/src/kernel/mem/seg.h
@@ -1,6 +1,9 @@
 #ifndef DEF_SEG_H
 #define DEF_SEG_H
 
+/*	Segments are pieces of usable memory in a process' address space.
+	They have nothing to do with GDT segments, they are created over paging. */
+
 #include "paging.h"
 
 struct segment_map;
@@ -8,6 +11,7 @@ struct segment {
 	void* seg_data;
 	int mappings;
 
+	// these 4 functions must not be used directly by anyone
 	struct segment_map* (*map)(struct segment* seg, struct page_directory* pagedir, size_t offset);
 	void (*unmap)(struct segment_map*);
 	void (*delete)(struct segment* seg);
@@ -21,8 +25,9 @@ struct segment_map {
 	struct segment_map *next;
 };
 
-//parameter offset in seg_map needs not be used
+//parameter offset in seg_map doesn't need to be used
 struct segment_map *seg_map(struct segment* seg, struct page_directory* pagedir, size_t offset);
+/*	When unmapping a segment, the segment is deleted if it is not mapped anywhere anymore. */
 void seg_unmap(struct segment_map* map);
 
 /// *************************************     SIMPLESEG stuff *****************
@@ -32,11 +37,7 @@ struct simpleseg {
 	size_t start, len;
 };
 
-struct segment* simpleseg_make(size_t start, size_t len, int writable); 
-struct segment_map* simpleseg_map(struct segment* seg, struct page_directory* pagedir, size_t offset);
-void simpleseg_unmap(struct segment_map*);
-void simpleseg_delete(struct segment *seg);
-int simpleseg_handleFault(struct segment_map* map, size_t addr, int write);
+struct segment* simpleseg_make(size_t start, size_t len, int writable);
 int simpleseg_resize(struct segment_map *map, size_t len);
 
 #endif
diff --git a/src/kernel/task/idt.c b/src/kernel/task/idt.c
index 80f13db..887ebf7 100644
--- a/src/kernel/task/idt.c
+++ b/src/kernel/task/idt.c
@@ -67,6 +67,8 @@ struct idt_ptr idt_ptr;
 static int_callback irq_handlers[16] = {0};
 static struct thread* irq_wakeup[16] = {0};
 
+/*	Called in idt_.asm when an exception fires (interrupt 0 to 31).
+	Tries to handle the exception, panics if fails. */
 void idt_isrHandler(struct registers regs) {
 	if ((regs.int_no == 14 && paging_fault(&regs) != 0) || regs.int_no != 14) {
 		if (tasking_handleException(&regs) == 0) {
@@ -80,6 +82,8 @@ void idt_isrHandler(struct registers regs) {
 	}
 } 
 
+/*	Called in idt_.asm when an IRQ fires (interrupt 32 to 47)
+	Possibly wakes up a thread that was waiting, possibly calls a handler. */
 void idt_irqHandler(struct registers regs) {
 	uint32_t doSwitch = (regs.err_code == 0);	//IRQ0 = timer
 	if (regs.err_code > 7) {
@@ -97,14 +101,15 @@ void idt_irqHandler(struct registers regs) {
 	if (doSwitch) tasking_switch();
 }
 
+/*	Called in idt_.asm on a system call (interrupt 64).
+	Calls the correct syscall handler (if any). */
 void idt_syscallHandler(struct registers regs) {
-	if (syscalls[regs.eax] != 0) {
+	if (regs.eax < NUMBER_OF_SYSCALLS && syscalls[regs.eax] != 0) {
 		syscalls[regs.eax](&regs);
-	} else {
-		monitor_write("Unhandled syscall...\n");
 	}
 }
 
+/*	For internal use only. Sets up an entry of the IDT with given parameters. */
 static void idt_setGate(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;
@@ -114,6 +119,7 @@ static void idt_setGate(uint8_t num, uint32_t base, uint16_t sel, uint8_t flags)
 	idt_entries[num].flags = flags | 0x60;
 }
 
+/*	Remaps the IRQs. Sets up the IDT. */
 void idt_init() {
 	idt_ptr.limit = (sizeof(struct idt_entry) * 256) - 1;
 	idt_ptr.base = (uint32_t)&idt_entries;
@@ -189,12 +195,14 @@ void idt_init() {
 	monitor_write("[IDT] ");
 }
 
+/*	Sets up an IRQ handler for given IRQ. */
 void idt_handleIrq(int number, int_callback func) {
 	if (number < 16 && number >= 0) {
 		irq_handlers[number] = func;
 	}
 }
 
+/*	Tells the IRQ handler to wake up the current thread when specified IRQ fires. */
 void idt_waitIrq(int number) {
 	if (number < 16 && number >= 0 && proc_priv() <= PL_DRIVER) {
 		irq_wakeup[number] = current_thread;
diff --git a/src/kernel/task/idt.h b/src/kernel/task/idt.h
index b12d6c5..1ac03e2 100644
--- a/src/kernel/task/idt.h
+++ b/src/kernel/task/idt.h
@@ -1,6 +1,12 @@
 #ifndef DEF_IDT_H
 #define DEF_IDT_H
 
+/*	The IDT is the system descriptor table that tells the CPU what to do when an interrupt fires.
+	There are three categories of interrupts :
+	- Exceptions ; ex: page fault, divide by 0
+	- IRQ : interrupts caused by hardware
+	- System calls : when an applications asks the system to do something */
+
 #include <types.h>
 
 struct idt_entry {
diff --git a/src/kernel/task/syscall.c b/src/kernel/task/syscall.c
index a5142eb..41cd0ea 100644
--- a/src/kernel/task/syscall.c
+++ b/src/kernel/task/syscall.c
@@ -38,7 +38,7 @@ static void thread_new_sc(struct registers* r) {
 	thread_new(current_thread->process, (thread_entry)r->ebx, (void*)r->ecx);
 }
 
-int_callback syscalls[] = {
+int_callback syscalls[NUMBER_OF_SYSCALLS] = {
 	thread_exit_sc,			//0
 	schedule_sc,
 	thread_sleep_sc,
diff --git a/src/kernel/task/syscall.h b/src/kernel/task/syscall.h
index 54af108..f03be55 100644
--- a/src/kernel/task/syscall.h
+++ b/src/kernel/task/syscall.h
@@ -3,6 +3,8 @@
 
 #include "idt.h"
 
+#define NUMBER_OF_SYSCALLS 32
+
 extern int_callback syscalls[];
 
 #endif
diff --git a/src/kernel/task/task.c b/src/kernel/task/task.c
index 8afc609..d8670a0 100644
--- a/src/kernel/task/task.c
+++ b/src/kernel/task/task.c
@@ -17,19 +17,20 @@ static void thread_exit2(uint32_t reason);
 static void thread_delete(struct thread *th);
 static void process_delete(struct process *pr);
 
+static uint32_t thread_runnable(struct thread *th);
+
 //From task_.asm
 extern uint32_t read_eip();
 extern void task_idle(void*);
 
-static uint32_t thread_runnable(struct thread *th);
-
 static uint32_t nextpid = 1;
-
 struct process *processes = 0, *kernel_process;
 struct thread *threads = 0, *current_thread = 0, *idle_thread;
 
 uint32_t tasking_tmpStack[KSTACKSIZE];
 
+/*	Sets up tasking. Called by kmain on startup.
+	Creates a kernel process and an IDLE thread in it. */
 void tasking_init() {
 	cli();
 	kernel_process = kmalloc(sizeof(struct process));	//This process must be hidden to users
@@ -45,6 +46,19 @@ void tasking_init() {
 	monitor_write("[Tasking] ");
 }
 
+/*	Called by the paging functions when a page table is allocated in the kernel space (>0xE0000000).
+	Updates the page directories of all the processes. */
+void tasking_updateKernelPagetable(uint32_t idx, struct page_table *table, uint32_t tablephysical) {
+	if (idx < 896) return;
+	struct process* it = processes;
+	while (it != 0) {
+		it->pagedir->tables[idx] = table;
+		it->pagedir->tablesPhysical[idx] = tablephysical;
+		it = it->next;
+	}
+}
+
+/*	Looks through the list of threads, finds the next thread to run. */
 static struct thread *thread_next() {
 	if (current_thread == 0 || current_thread == idle_thread) current_thread = threads;
 	struct thread *ret = current_thread;
@@ -60,6 +74,7 @@ static struct thread *thread_next() {
 	}
 }
 
+/*	Called when a timer IRQ fires. Does a context switch. */
 void tasking_switch() {
 	if (threads == 0) PANIC("No more threads to run !");
 	asm volatile("cli");
@@ -94,16 +109,8 @@ void tasking_switch() {
 		: : "r"(current_thread->ebp), "r"(current_thread->esp), "r"(current_thread->eip));
 }
 
-void tasking_updateKernelPagetable(uint32_t idx, struct page_table *table, uint32_t tablephysical) {
-	if (idx < 896) return;
-	struct process* it = processes;
-	while (it != 0) {
-		it->pagedir->tables[idx] = table;
-		it->pagedir->tablesPhysical[idx] = tablephysical;
-		it = it->next;
-	}
-}
-
+/*	Called when an exception happens. Provides a stack trace if it was in kernel land.
+	Ends the thread for most exceptions, ends the whole process for page faults. */
 uint32_t tasking_handleException(struct registers *regs) {
 	if (current_thread == 0) return 0;	//No tasking yet
 	NL; WHERE; monitor_write("Unhandled exception : ");
@@ -134,6 +141,7 @@ uint32_t tasking_handleException(struct registers *regs) {
 	return 0;
 }
 
+/*	Makes the current thread sleep. */
 void thread_sleep(uint32_t msecs) {
 	if (current_thread == 0) return;
 	current_thread->state = TS_SLEEPING;
@@ -141,20 +149,25 @@ void thread_sleep(uint32_t msecs) {
 	tasking_switch();
 }
 
+/*	Puts the current thread in an inactive state. */
 void thread_goInactive() {
 	current_thread->state = TS_WAKEWAIT;
 	tasking_switch();
 }
 
+/*	Wakes up the given thread. */
 void thread_wakeUp(struct thread* t) {
 	if (t->state == TS_WAKEWAIT) t->state = TS_RUNNING;
 }
 
+/*	Returns the privilege level of the current process. */
 int proc_priv() {
 	if (current_thread == 0 || current_thread->process == 0) return PL_UNKNOWN;
 	return current_thread->process->privilege;
 }
 
+/*	For internal use only. Called by thread_exit_stackJmp on a stack that will not be deleted.
+	Exits current thread or process, depending on the reason. */
 void thread_exit2(uint32_t reason) {		//See EX_TH_* defines in task.h
 	/*
 	 * if reason == EX_TH_NORMAL, it is just one thread exiting because it has to
@@ -170,9 +183,12 @@ void thread_exit2(uint32_t reason) {		//See EX_TH_* defines in task.h
 		process_delete(pr);
 	}
 	retrn:
+	sti();
 	tasking_switch();
 }
 
+/*	For internal use only. Called by thread_exit and process_exit.
+	Switches to a stack that will not be deleted when current thread is deleted. */
 void thread_exit_stackJmp(uint32_t reason) {
 	cli();
 	uint32_t *stack;
@@ -188,15 +204,18 @@ void thread_exit_stackJmp(uint32_t reason) {
 			"r"(stack), "r"(stack), "r"(thread_exit2), "r"(kernel_pagedir->physicalAddr));
 }
 
+/*	System call. Exit the current thread. */
 void thread_exit() {
 	thread_exit_stackJmp(EX_TH_NORMAL);
 }
 
+/*	System call. Exit the current process. */
 void process_exit(uint32_t retval) {
 	if (retval == EX_TH_NORMAL || retval == EX_TH_EXCEPTION) retval = EX_PR_EXCEPTION;
 	thread_exit_stackJmp(retval);
 }
 
+/*	Nonzero if given thread is not in a waiting state. */
 static uint32_t thread_runnable(struct thread *t) {
 	if (t->state == TS_RUNNING) return 1;
 	if (t->state == TS_SLEEPING && timer_time() >= t->timeWait) {
@@ -206,6 +225,9 @@ static uint32_t thread_runnable(struct thread *t) {
 	return 0;
 }
 
+/*	For internal use only. This is called when a newly created thread first runs
+	(its address is the value given for EIP).
+	It switches to user mode if necessary and calls the entry point. */
 static void thread_run(struct thread *thread, thread_entry entry_point, void *data) {
 	pagedir_switch(thread->process->pagedir);
 	if (thread->process->privilege >= PL_SERVICE) {	//User mode !
@@ -248,6 +270,9 @@ static void thread_run(struct thread *thread, thread_entry entry_point, void *da
 	thread_exit(0);
 }
 
+/*	Creates a new thread for given process.
+	Allocates a kernel stack and a user stack if necessary.
+	Sets up the kernel stack for values to be passed to thread_run. */
 struct thread *thread_new(struct process *proc, thread_entry entry_point, void *data) {
 	struct thread *t = kmalloc(sizeof(struct thread));
 	t->process = proc;
@@ -284,6 +309,7 @@ struct thread *thread_new(struct process *proc, thread_entry entry_point, void *
 	return t;
 }
 
+/*	Creates a new process. Creates a struct process and fills it up. */
 struct process *process_new(struct process* parent, uint32_t uid, uint32_t privilege) {
 	struct process* p = kmalloc(sizeof(struct process));
 	p->pid = (nextpid++);
@@ -307,6 +333,7 @@ struct process *process_new(struct process* parent, uint32_t uid, uint32_t privi
 	return p;
 }
 
+/*	Deletes given thread, freeing the stack(s). */
 static void thread_delete(struct thread *th) {
 	if (threads == th) {
 		threads = th->next;
@@ -327,6 +354,7 @@ static void thread_delete(struct thread *th) {
 	kfree(th);
 }
 
+/*	Deletes a process. First, deletes all its threads. Also deletes the corresponding page directory. */
 static void process_delete(struct process *pr) {
 	struct thread *it = threads;
 	while (it != 0) {
@@ -354,6 +382,7 @@ static void process_delete(struct process *pr) {
 	kfree(pr);
 }
 
+/*	System call. Called by the app to define the place for the heap. */
 int process_setheapseg(size_t start, size_t end) {		//syscall
 	struct process *p = current_thread->process;
 	if (start >= 0xE0000000 || end >= 0xE0000000) return -1;
diff --git a/src/kernel/task/task.h b/src/kernel/task/task.h
index 3dad63d..ef93c9f 100644
--- a/src/kernel/task/task.h
+++ b/src/kernel/task/task.h
@@ -57,13 +57,14 @@ void tasking_updateKernelPagetable(uint32_t idx, struct page_table *table, uint3
 uint32_t tasking_handleException(struct registers *regs);
 
 void thread_sleep(uint32_t msecs);
-void thread_goInactive();	//Blocks the current thread. another one must be there to wake it up at some point.
+void thread_goInactive();	//Blocks the current thread. it is then waked up by another thread or a system event. 
 void thread_wakeUp(struct thread *t);
 int proc_priv();	//Returns current privilege level
-void thread_exit();
-void process_exit(uint32_t retval);
 struct thread * thread_new(struct process *proc, thread_entry entry_point, void *data);
 struct process* process_new(struct process *parent, uint32_t uid, uint32_t privilege);
+
+void thread_exit();	//syscall
+void process_exit(uint32_t retval);	//syscall
 int process_setheapseg(size_t start, size_t end);	//syscall
 
 #endif
diff --git a/src/kernel/task/timer.c b/src/kernel/task/timer.c
index e924657..1ec1523 100644
--- a/src/kernel/task/timer.c
+++ b/src/kernel/task/timer.c
@@ -5,6 +5,8 @@
 
 static uint32_t tick = 0, frequency = 0, uptime = 0;
 
+/*	Called when IRQ0 fires. Updates the uptime variable.
+	DOES NOT provoke a task switch. The task switch is called in idt.c (IRQ handler). */
 void timer_callback(struct registers *regs) {
 	tick++;
 	if (tick == frequency) {
@@ -13,12 +15,15 @@ void timer_callback(struct registers *regs) {
 	}
 }
 
+/*	Accessor function to get machine uptime. */
 uint32_t timer_uptime() { return uptime; }
 
+/*	Accessor function, gets uptime in miliseconds. */
 uint32_t timer_time() {
 	return (uptime * 1000) + (tick * 1000 / frequency);
 }
 
+/*	Called by kmain. Sets up the PIT and the IRQ0 handler. */
 void timer_init(uint32_t freq) {
 	frequency = freq;
 
-- 
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