diff --git a/include/asm/io.h b/include/asm/io.h
index bc51561472e9d42e432f7cf9a635905fda7eabb9..b2f16c15bae528f9efb79f34f814c3f4a0be53ad 100644
--- a/include/asm/io.h
+++ b/include/asm/io.h
@@ -1,10 +1,31 @@
 #ifndef _IO_H
 #define _IO_H
 
+#define outb(value,port) \
+__asm__ ("outb %%al,%%dx"::"a" (value),"d" (port))
+
+
+#define inb(port) ({ \
+i   unsigned char _v; \
+    __asm__ volatile ("inb %%dx,%%al":"=a" (_v):"d" (port)); \
+    _v; \
+})
+
+
 #define outb_p(value, port)     \
 __asm__("outb %%al, %%dx\n"     \
         "\tjmp 1f\n"            \
         "1:\tjmp 1f\n"          \
         "1:" :: "a"(value), "d"(port))
 
+
+#define inb_p(port) ({ \
+unsigned char _v; \
+__asm__ volatile ("inb %%dx,%%al\n" \
+    "\tjmp 1f\n" \
+    "1:\tjmp 1f\n" \
+    "1:":"=a" (_v):"d" (port)); \
+_v; \
+})
+
 #endif
diff --git a/include/linux/sched.h b/include/linux/sched.h
index dce71186b97e61d967b13ab8e2da1dfedcb58bbc..2278399dac843f834d5e7c5afe40b319ceb79644 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1,6 +1,8 @@
 #ifndef _SCHED_H
 #define _SCHED_H
 
+#define HZ 100
+
 #include <linux/head.h>
 #include <linux/mm.h>
 
diff --git a/kernel/sched.c b/kernel/sched.c
index b7a5043608e01042cdb0e8f5bc1d9145cf06057b..503810ee3c943cabecea03ff5bd45cffcd6ee4b7 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1,10 +1,13 @@
 #include <linux/sched.h>
 
 #include <asm/system.h>
-
+#include <asm/io.h>
+ 
+#define LATCH (1193180/HZ)
 #define PAGE_SIZE 4096
 
 extern int system_call();
+extern void timer_interrupt();
 
 union task_union {
     struct task_struct task;
@@ -21,6 +24,14 @@ struct
     short b;
 } stack_start = {&user_stack[PAGE_SIZE >> 2], 0x10};
 
+void do_timer(long cpl) {
+    static unsigned char c = '0';
+    if (c > 127) {
+        c = '0';
+    }
+    printk("\b%c", c++);
+}
+
 void sched_init() {
     struct desc_struct* p;
     set_tss_desc(gdt + FIRST_TSS_ENTRY, &(init_task.task.tss));
@@ -28,6 +39,14 @@ void sched_init() {
     __asm__("pushfl; andl $0xffffbfff, (%esp); popfl");
     ltr(0);
     lldt(0);
+
+    /* open the clock interruption! */
+    outb_p(0x36, 0x43);
+    outb_p(LATCH & 0xff, 0x40);
+    outb(LATCH >> 8, 0x40);
+    set_intr_gate(0x20, &timer_interrupt);
+    outb(inb_p(0x21) & ~0x01, 0x21);
+
     set_system_gate(0x80, &system_call);
 }
 
diff --git a/kernel/sys_call.S b/kernel/sys_call.S
index a71dab3cbcbaa2e5de6aec6443a0aac9d6bb6fb2..a75406c7e14c02cabf34e35d63482418bb0a1589 100644
--- a/kernel/sys_call.S
+++ b/kernel/sys_call.S
@@ -1,11 +1,24 @@
 .code32
 .text
-.globl system_call
+.globl system_call, timer_interrupt
+
+EAX        = 0x00
+EBX        = 0x04
+ECX        = 0x08
+EDX        = 0x0C
+FS         = 0x10
+ES         = 0x14
+DS         = 0x18
+EIP        = 0x1c
+CS         = 0x20
+EFLAGS     = 0x24
+OLDESP     = 0x28
+OLDSS      = 0x2c
+
 int_msg:
-    .asciz  "In kernel interrupt"
+    .asciz  "In kernel interrupt\n\r"
 
 system_call:
-    /* we do not have function _printk now, so trick it */
     pushl %eax
     pushl %ecx
     pushl %edx
@@ -28,3 +41,35 @@ system_call:
     popl  %eax
     iret
 
+ret_from_sys_call:
+    popl %eax
+    popl %ebx
+    popl %ecx
+    popl %edx
+    popw %fs
+    popw %es
+    popw %ds
+    iret
+
+.align 4
+timer_interrupt:
+    pushw %ds
+    pushw %es
+    pushw %fs
+    pushl %edx
+    pushl %ecx
+    pushl %ebx
+    pushl %eax
+    movl  $0x10, %eax
+    movw  %ax, %ds
+    movw  %ax, %es
+    movl  $0x17, %eax
+    movw  %ax, %fs
+    movb  $0x20, %al
+    outb  %al, $0x20
+    movl  CS(%esp), %eax
+    andl  $3, %eax
+    pushl %eax
+    call  do_timer
+    addl  $4, %esp
+    jmp   ret_from_sys_call