diff --git a/core/interrupt.h b/core/interrupt.h
index 7bef8c9..50ac724 100644
--- a/core/interrupt.h
+++ b/core/interrupt.h
@@ -1,13 +1,21 @@
 #pragma once
 #include "stdarg.h"
 
-struct interrupt_frame;
 
-//Exception
+// c.f. intel software-developer-vol-1 6.4.1
+struct interrupt_frame {
+        uint32_t eip;
+        uint32_t cs;
+        uint32_t eflags;
+        uint32_t esp;
+        uint32_t ss;
+};
+
+// Exception
 void print_handler(struct interrupt_frame *frame, ulong error_code);
 void pagefault_handler(struct interrupt_frame *frame, ulong error_code);
 
-//IRQ
+// IRQ
 void keyboard_handler(struct interrupt_frame *frame);
 void timer_handler(struct interrupt_frame *frame);
 void serial_handler(struct interrupt_frame *frame);
diff --git a/core/main.c b/core/main.c
index a1812b2..c958b59 100644
--- a/core/main.c
+++ b/core/main.c
@@ -70,17 +70,16 @@ void kmain(unsigned long magic, unsigned long addr)
         }
 
         if (CHECK_FLAG(mbi->flags, 6)) {
-            struct multiboot_mmap_entry *mmap = (struct multiboot_mmap_entry*)mbi->mmap_addr;
+            struct multiboot_mmap_entry *mmap = (struct multiboot_mmap_entry *)mbi->mmap_addr;
             uint size = mbi->mmap_length / sizeof(struct multiboot_mmap_entry);
-            printf("mmap buffer at %d size %d %d\n", mbi->mmap_addr, mbi->mmap_length, sizeof(multiboot_memory_map_t) );
-            for (uint i = 0; i < size; i++){
+            printf("mmap buffer at %d size %d %d\n", mbi->mmap_addr, mbi->mmap_length,
+                   sizeof(multiboot_memory_map_t));
+            for (uint i = 0; i < size; i++) {
                 printf("base_addr_high = 0x%x, base_addr_low = 0x%x, "
-                        "length_high = 0x%x, length_low = 0x%x, type = 0x%x\n",
-                    (unsigned)  (mmap[i].addr >> 32),
-                     (unsigned) (mmap[i].addr & 0xffffffff),
-                     (unsigned) (mmap[i].len >> 32),
-                     (unsigned) (mmap[i].len & 0xffffffff),
-                        (uint32_t)mmap[i].type);
+                       "length_high = 0x%x, length_low = 0x%x, type = 0x%x\n",
+                       (unsigned)(mmap[i].addr >> 32), (unsigned)(mmap[i].addr & 0xffffffff),
+                       (unsigned)(mmap[i].len >> 32), (unsigned)(mmap[i].len & 0xffffffff),
+                       (uint32_t)mmap[i].type);
             }
         }
     }
@@ -100,6 +99,7 @@ void kmain(unsigned long magic, unsigned long addr)
 
     printf("Setting up IRQ handlers\n");
     irqSetRoutine(IRQ_KEYBOARD, keyboard_handler);
+    irqSetRoutine(IRQ_TIMER, timer_handler);
 
     printf("Enabling HW interrupts\n");
     exceptionSetRoutine(EXCEPTION_DOUBLE_FAULT, print_handler);
diff --git a/drivers/pit.c b/drivers/pit.c
index 697d76c..c600a3e 100644
--- a/drivers/pit.c
+++ b/drivers/pit.c
@@ -11,6 +11,5 @@ int pitSetup(unsigned int freq)
 	outb(PIT_CHAN_0, divisor & 0xFF);
 	outb(PIT_CHAN_0, divisor >> 8u);
 
-	irqSetRoutine(IRQ_TIMER, timer_handler);
 	return 0;
 }