diff --git a/CMakeLists.txt b/CMakeLists.txt
index e25c6fc..a873ef1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.15)
 project(new_kernel C ASM)
-set(CMAKE_VERBOSE_MAKEFILE ON)
+#set(CMAKE_VERBOSE_MAKEFILE ON)
 set(CMAKE_C_FLAGS "-g -ffreestanding -Wall -Wextra -fno-exceptions -fno-stack-protector -nostdinc -nostdlib -fno-pie -m32")
 set(CMAKE_ASM_NASM_OBJECT_FORMAT "elf")
 set(CMAKE_ASM_FLAGS --32)
diff --git a/kernel/cpu/idt.h b/kernel/cpu/idt.h
index de9cbb2..af39a1f 100644
--- a/kernel/cpu/idt.h
+++ b/kernel/cpu/idt.h
@@ -1,7 +1,7 @@
 //
 // Created by rick on 8/18/19.
 //
-#include "../types.h"
+#include <types.h>
 
 #ifndef MY_KERNEL_IDT_H
 #define MY_KERNEL_IDT_H
diff --git a/kernel/cpu/isr.c b/kernel/cpu/isr.c
index 0057c9f..dd9c2e7 100644
--- a/kernel/cpu/isr.c
+++ b/kernel/cpu/isr.c
@@ -9,6 +9,8 @@
 #include <libc/libc.h>
 #include <drivers/ports.h>
 
+#define PIC_END_OF_INTERRUPT 0x20
+
 isr_t interrupt_handlers[256];
 
 void isr_install() {
@@ -133,11 +135,11 @@ void register_interrupt_handler(u8 n, isr_t handler) {
 void irq_handler(registers_t r) {
     /* After every interrupt we need to send an EOI to the PICs
      * or they will not send another interrupt again */
-    if (r.int_no >= 40) port_byte_out(0xA0, 0x20); /* slave */
-    port_byte_out(0x20, 0x20); /* master */
+    if (r.int_no >= 40) port_byte_out(PORT_PIC_SLAVE_COMMAND, PIC_END_OF_INTERRUPT); /* slave */
+    port_byte_out(PORT_PIC_MASTER_COMMAND, PIC_END_OF_INTERRUPT); /* master */
 
     /* Handle the interrupt in a more modular way */
-    if (interrupt_handlers[r.int_no] != 0) {
+    if (interrupt_handlers[r.int_no] != NULL) {
         isr_t handler = interrupt_handlers[r.int_no];
         handler(r);
     }
diff --git a/kernel/cpu/isr.h b/kernel/cpu/isr.h
index 01afdd7..982534b 100644
--- a/kernel/cpu/isr.h
+++ b/kernel/cpu/isr.h
@@ -2,7 +2,7 @@
 // Created by rick on 8/18/19.
 //
 
-#include "../types.h"
+#include <types.h>
 
 #ifndef MY_KERNEL_ISR_H
 #define MY_KERNEL_ISR_H
diff --git a/kernel/cpu/timer.c b/kernel/cpu/timer.c
index d5e2c9d..b20571b 100644
--- a/kernel/cpu/timer.c
+++ b/kernel/cpu/timer.c
@@ -7,6 +7,28 @@
 #include <drivers/ports.h>
 #include <cpu/isr.h>
 
+// https://wiki.osdev.org/PIT
+#define PIT_MODE_BIN_BCD                            (1 << 0)
+#define PIT_MODE_BIN                                (0 << 0)
+#define PIT_MODE_BCD                                (1 << 0)
+#define PIT_GENERATOR_MODE                          (0b111 << 1)
+#define PIT_MODE_INTERRUPT_ON_TERMINAL_COUNT        (0b000 < 1)
+#define PIT_MODE_HARDWARE_RETRIGGERABLE_ONE_SHOT    (0b001 < 1)
+#define PIT_MODE_HARDWARE_RATE_GENERATOR            (0b010 < 1)
+#define PIT_MODE_HARDWARE_SQUARE_WAVE_GENERATOR     (0b011 < 1)
+#define PIT_MODE_SOFTWARE_TRIGGERED_STROBE          (0b100 << 1)
+#define PIT_MODE_HARDWARE_TRIGGERED_STROBE          (0b101 << 1)
+#define PIT_ACCESS_MODE                             (0b11 << 4)
+#define PIT_ACCESS_MODE_LATCH_COUNT                 (0b00 << 4)
+#define PIT_ACCESS_MODE_L                           (0b01 << 4)
+#define PIT_ACCESS_MODE_H                           (0b10 << 4)
+#define PIT_ACCESS_MODE_LH                          (0b11 << 4)
+#define PIT_CHANNEL                                 (0b11 << 6)
+#define PIT_CHANNEL_0                               (0b00 << 6)
+#define PIT_CHANNEL_1                               (0b01 << 6)
+#define PIT_CHANNEL_2                               (0b10 << 6)
+#define PIT_CHANNEL_READ_BACK                       (0b11 << 6)
+
 u32 tick = 0;
 
 static void timer_callback(registers_t regs) {
@@ -19,7 +41,7 @@ int init_timer(u32 freq) {
     u32 divisor = 1193180 / freq;
     u8 low = (u8) (divisor & 0xFF);
     u8 high = (u8) ((divisor >> 8) & 0xFF);
-    port_byte_out(PORT_PIT_COMMAND, PIT_MODE_BIN | PIT_MODE_SQUARE_WAVE | PIT_ACCESS_MODE_HL | PIT_CHANNEL_0);
+    port_byte_out(PORT_PIT_COMMAND, PIT_MODE_BIN | PIT_MODE_HARDWARE_SQUARE_WAVE_GENERATOR | PIT_ACCESS_MODE_LH | PIT_CHANNEL_0);
     port_byte_out(PORT_PIT_DATA_0, low);
     port_byte_out(PORT_PIT_DATA_0, high);
     return 0;
diff --git a/kernel/cpu/timer.h b/kernel/cpu/timer.h
index 569348a..a91e2c3 100644
--- a/kernel/cpu/timer.h
+++ b/kernel/cpu/timer.h
@@ -5,7 +5,7 @@
 #ifndef MY_KERNEL_TIMER_H
 #define MY_KERNEL_TIMER_H
 
-#include "../types.h"
+#include <types.h>
 
 int init_timer(u32 freq);
 
diff --git a/kernel/drivers/ports.h b/kernel/drivers/ports.h
index fad2d61..11db0a0 100644
--- a/kernel/drivers/ports.h
+++ b/kernel/drivers/ports.h
@@ -1,6 +1,11 @@
 #ifndef MY_KERNEL_DRIVERS_PORT_H
 #define MY_KERNEL_DRIVERS_PORT_H
 
+#define PORT_PIC_MASTER_COMMAND 0x20
+#define PORT_PIC_MASTER_DATA 0x21
+#define PORT_PIC_SLAVE_COMMAND 0xA0
+#define PORT_PIC_SLAVE_DATA 0xA1
+
 //http://www.osdever.net/FreeVGA/vga/crtcreg.htm#0A
 #define PORT_REG_SCREEN_CTRL 0x3d4
 #define PORT_REG_SCREEN_CTRL_CURSOR_H 0x0E
@@ -26,11 +31,6 @@
 
 // https://wiki.osdev.org/PIT
 #define PORT_PIT_COMMAND 0x43
-#define PIT_MODE_BIN 0x0
-#define PIT_MODE_HW_STROBE 0b0101
-#define PIT_MODE_SQUARE_WAVE 0b0110
-#define PIT_ACCESS_MODE_HL 0b000011
-#define PIT_CHANNEL_0 0b00000000
 #define PORT_PIT_DATA_0 0x40
 #define PORT_PIT_DATA_1 0x41
 #define PORT_PIT_DATA_3 0x42
diff --git a/kernel/drivers/serial.c b/kernel/drivers/serial.c
index 595c066..3ad0744 100644
--- a/kernel/drivers/serial.c
+++ b/kernel/drivers/serial.c
@@ -6,16 +6,73 @@
 #include <types.h>
 #include <drivers/ports.h>
 
+#define SERIAL_INTERRUPT_DATA_AVAILABLE     (1 << 0)
+#define SERIAL_INTERRUPT_TRANSMITTER_EMPTY  (1 << 1)
+#define SERIAL_INTERRUPT_BREAK_ERROR        (1 << 2)
+#define SERIAL_INTERRUPT_STATUS_CHANGE      (1 << 3)
+
+#define LINE_STATUS_DATA_READY                          (1 << 0)
+#define LINE_STATUS_OVERRUN_ERROR                       (1 << 1)
+#define LINE_STATUS_PARITY_ERROR                        (1 << 2)
+#define LINE_STATUS_FRAMING_ERROR                       (1 << 3)
+#define LINE_STATUS_BREAK_INDICATOR                     (1 << 4)
+#define LINE_STATUS_TRANSMITTER_HOLDING_REGISTER_EMPTY  (1 << 5)
+#define LINE_STATUS_TRANSMITTER_EMPTY                   (1 << 6)
+#define LINE_STATUS_IMPENDING_ERROR                     (1 << 7)
+
+#define LINE_CONTROL_DATA_BITS_5        (0b00)
+#define LINE_CONTROL_DATA_BITS_6        (0b01)
+#define LINE_CONTROL_DATA_BITS_7        (0b10)
+#define LINE_CONTROL_DATA_BITS_8        (0b11)
+#define LINE_CONTROL_STOP_BITS_1        (0 << 2)
+#define LINE_CONTROL_STOP_BITS_1_5_2    (1 << 2)
+#define LINE_CONTROL_PARTY_NONE         (0b000 << 3)
+#define LINE_CONTROL_PARTY_ODD          (0b001 << 3)
+#define LINE_CONTROL_PARTY_EVEN         (0b010 << 3)
+#define LINE_CONTROL_PARTY_MARK         (0b101 << 3)
+#define LINE_CONTROL_PARTY_SPACE        (0b111 << 3)
+#define LINE_CONTROL_DIVISOR            (1 << 7)
+
+#define FIFO_CONTROL_ENABLE                 (1 << 0)
+#define FIFO_CONTROL_CLEAR_RECEIVE          (1 << 1)
+#define FIFO_CONTROL_CLEAR_TRANSMIT         (1 << 2)
+#define FIFO_CONTROL_DMA_MODE_SELECT        (1 << 3)
+// reserved
+#define FIFO_CONTROL_64_BYTE_ENABLE         (1 << 5)
+#define FIFO_CONTROL_TRIGGER_LEVEL_1_BYTE   (0b00 << 6)
+#define FIFO_CONTROL_TRIGGER_LEVEL_4_BYTE   (0b01 << 6)
+#define FIFO_CONTROL_TRIGGER_LEVEL_8_BYTE   (0b10 << 6)
+#define FIFO_CONTROL_TRIGGER_LEVEL_14_BYTE  (0b11 << 6)
+
+#define MODEM_CONTROL_DATA_TERMINAL_READY       (1 << 0)
+#define MODEM_CONTROL_REQUEST_TO_SEND           (1 << 1)
+#define MODEM_CONTROL_AUX_OUTPUT_1              (1 << 2)
+#define MODEM_CONTROL_AUX_OUTPUT_2              (1 << 3)
+#define MODEM_CONTROL_LOOPBACK_MODE             (1 << 4)
+#define MODEM_CONTROL_AUTOFLOW_CONTROL_ENABLED  (1 << 5)
+
 int serial_init() {
-    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_INTERRUPT, 0x00);    // Disable all interrupts
-    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_LINE_CONTROL, 0x80);    // Enable DLAB (set baud rate divisor)
+    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_INTERRUPT, 0);    // Disable all interrupts
+    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_LINE_CONTROL,
+                  LINE_CONTROL_DIVISOR);    // Enable DLAB (set baud rate divisor)
     port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_DLAB_LSB, 0x03);    // Set divisor to 3 (lo byte) 38400 baud
     port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_DLAB_MSB, 0x00);    //                  (hi byte)
-    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_LINE_CONTROL, 0x03);    // 8 bits, no parity, one stop bit
+    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_LINE_CONTROL,
+                  LINE_CONTROL_DATA_BITS_8);    // 8 bits, no parity, one stop bit
     port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_INTERRUPT_ID_FIFO,
-                  0xC7);    // Enable FIFO, clear them, with 14-byte threshold
-    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_MODEM_CONTROL, 0x0B);    // IRQs enabled, RTS/DSR set
-    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_MODEM_CONTROL, 0x1E);    // Set in loopback mode, test the serial chip
+                  FIFO_CONTROL_ENABLE
+                  | FIFO_CONTROL_CLEAR_RECEIVE
+                  | FIFO_CONTROL_CLEAR_TRANSMIT
+                  | FIFO_CONTROL_TRIGGER_LEVEL_14_BYTE);    // Enable FIFO, clear them, with 14-byte threshold
+    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_MODEM_CONTROL,
+                  MODEM_CONTROL_DATA_TERMINAL_READY
+                  | MODEM_CONTROL_REQUEST_TO_SEND
+                  | MODEM_CONTROL_AUX_OUTPUT_2);    // IRQs enabled, RTS/DSR set
+    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_MODEM_CONTROL,
+                  MODEM_CONTROL_REQUEST_TO_SEND
+                  | MODEM_CONTROL_AUX_OUTPUT_1
+                  | MODEM_CONTROL_AUX_OUTPUT_2
+                  | MODEM_CONTROL_LOOPBACK_MODE);    // Set in loopback mode, test the serial chip
     port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_DATA,
                   0xAE);    // Test serial chip (send byte 0xAE and check if serial returns same byte)
 
@@ -26,12 +83,16 @@ int serial_init() {
 
     // If serial is not faulty set it in normal operation mode
     // (not-loopback with IRQs enabled and OUT#1 and OUT#2 bits enabled)
-    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_MODEM_CONTROL, 0x0F);
+    port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_MODEM_CONTROL,
+                  MODEM_CONTROL_DATA_TERMINAL_READY
+                  | MODEM_CONTROL_REQUEST_TO_SEND
+                  | MODEM_CONTROL_AUX_OUTPUT_1
+                  | MODEM_CONTROL_AUX_OUTPUT_2);
     return 0;
 }
 
 int is_transmit_empty() {
-    return port_byte_in(PORT_SERIAL_0 + PORT_SERIAL_LINE_STATUS) & 0x20;
+    return port_byte_in(PORT_SERIAL_0 + PORT_SERIAL_LINE_STATUS) & LINE_STATUS_TRANSMITTER_HOLDING_REGISTER_EMPTY;
 }
 
 void write_serial(char a) {
@@ -40,7 +101,7 @@ void write_serial(char a) {
     port_byte_out(PORT_SERIAL_0 + PORT_SERIAL_DATA, a);
 }
 
-void serial_kprint(char *msg) {
+void serial_kprint(const char *msg) {
     u32 i = 0;
     while (1) {
         char c = msg[i];
diff --git a/kernel/drivers/serial.h b/kernel/drivers/serial.h
index 049de5d..9ba5577 100644
--- a/kernel/drivers/serial.h
+++ b/kernel/drivers/serial.h
@@ -7,6 +7,6 @@
 
 int serial_init();
 
-void serial_kprint(char *msg);
+void serial_kprint(const char *msg);
 
 #endif //NEW_KERNEL_SERIAL_H
diff --git a/kernel/drivers/vgascreen.c b/kernel/drivers/vgascreen.c
index b345383..a271b68 100644
--- a/kernel/drivers/vgascreen.c
+++ b/kernel/drivers/vgascreen.c
@@ -31,7 +31,7 @@ void vga_clear_screen() {
     set_cursor_offset(0);
 }
 
-void kprint_at(char *message, int col, int row) {
+void kprint_at(const char *message, int col, int row) {
     int offset;
     if (col > 0 && row > 0) {
         offset = get_offset(col, row);
@@ -50,7 +50,7 @@ void kprint_at(char *message, int col, int row) {
 }
 
 
-void vga_kprint(char *message) {
+void vga_kprint(const char *message) {
     kprint_at(message, -1, -1);
 }
 
diff --git a/kernel/drivers/vgascreen.h b/kernel/drivers/vgascreen.h
index 7b485a9..7940ec0 100644
--- a/kernel/drivers/vgascreen.h
+++ b/kernel/drivers/vgascreen.h
@@ -29,6 +29,6 @@
 
 void vga_clear_screen();
 
-void vga_kprint(char *msg);
+void vga_kprint(const char *msg);
 
 #endif //MY_KERNEL_VGASCREEN_H
diff --git a/kernel/kernel.c b/kernel/kernel.c
index fcee24d..84dd133 100644
--- a/kernel/kernel.c
+++ b/kernel/kernel.c
@@ -7,7 +7,7 @@
 #include <mem/mem.h>
 #include <multiboot.h>
 #include <drivers/serial.h>
-#include "kprint.h"
+#include <kprint.h>
 
 char *msg_booted = "Booted Successfully!\n";
 
@@ -25,8 +25,7 @@ void kmain(multiboot_info_t *multiboot_info) {
 //    vga_print_string(msg_booted, VGA_WHITE | (VGA_DARK_GRAY << VGA_SHIFT_BG));
     kprint(msg_booted);
     kprint((char *) multiboot_info->boot_loader_name);
-    multiboot_memory_map_t *fe = multiboot_info->mmap_addr;
-
+//    multiboot_memory_map_t *fe = multiboot_info->mmap_addr;
 //    port_byte_out(0x3d4, 14);
 //    int pos = port_byte_in(0x3d5);
 //    pos <<= 8;
diff --git a/kernel/kprint.h b/kernel/kprint.h
index 86b5b34..d638b29 100644
--- a/kernel/kprint.h
+++ b/kernel/kprint.h
@@ -9,7 +9,7 @@
 
 #include <types.h>
 
-typedef void (*kprint_handler)(char *);
+typedef void (*kprint_handler)(const char *);
 
 void kprint_register(kprint_handler);