diff --git a/arch/x86/kernel/timer.c b/arch/x86/kernel/timer.c
index 1acf1fb1..4b3b2fd4 100644
--- a/arch/x86/kernel/timer.c
+++ b/arch/x86/kernel/timer.c
@@ -41,7 +41,7 @@ void schedule_entry(void);
  */
 static void timer_handler(struct regs *r)
 {
-	unsigned int tmp;
+	//unsigned int tmp;
 
 	/* Increment our 'tick counter' */
 	timer_ticks++;
@@ -50,10 +50,10 @@ static void timer_handler(struct regs *r)
          * Every TIMER_FREQ clocks (approximately 1 second), we will
 	 * display a message on the screen 
          */
-	tmp = (unsigned int) (timer_ticks & 0xFFFFFFFF);
+	/*tmp = (unsigned int) (timer_ticks & 0xFFFFFFFF);
 	if (tmp % TIMER_FREQ == 0) {
 		kputs("One second has passed\n");
-	}
+	}*/
 
 	if (current_task && !(current_task->ip)) {
 		current_task->ip = r->eip;
diff --git a/include/metalsvm/semaphore.h b/include/metalsvm/semaphore.h
new file mode 100644
index 00000000..9d7750a1
--- /dev/null
+++ b/include/metalsvm/semaphore.h
@@ -0,0 +1,98 @@
+/* 
+ * Copyright 2010 Stefan Lankes, Chair for Operating Systems,
+ *                               RWTH Aachen University
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * This file is part of MetalSVM.
+ */
+
+#ifndef __SEMAPHORE_H__
+#define __SEMAPHORE_H__
+
+#include <metalsvm/string.h>
+#include <metalsvm/tasks.h>
+#include <metalsvm/spinlocks.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+	unsigned int value;
+	tid_t queue[MAX_TASKS];
+	unsigned int pos;
+	spinlock_t lock;
+} sem_t;
+
+inline static void sem_init(sem_t* s, unsigned int v) {
+	unsigned int i;
+
+	s->value = v;
+	s->pos = 0;
+	for(i=0; i<MAX_TASKS; i++)
+		s->queue[i] = MAX_TASKS;
+	spinlock_init(&s->lock);
+}
+
+inline static void sem_destroy(sem_t* s) {
+	spinlock_destroy(&s->lock);
+}
+
+inline static int sem_wait(sem_t* s) {
+next_try:
+        spinlock_lock(&s->lock);
+	if (s->value > 0) {
+		s->value--;
+		spinlock_unlock(&s->lock);
+	} else {
+		s->queue[s->pos] = current_task->id;
+		s->pos = (s->pos + 1) % MAX_TASKS;
+		current_task->status = TASK_BLOCKED;
+		spinlock_unlock(&s->lock);
+		schedule();
+		goto next_try;
+	}
+
+	return 0;
+}
+
+inline static int sem_post(sem_t* s) {
+	spinlock_lock(&s->lock);
+	if (s->value > 0) {
+		s->value++;
+		spinlock_unlock(&s->lock);
+	} else {
+		unsigned int k, i;
+
+		i = s->pos;
+		s->value++;
+		for(k=0; k<MAX_TASKS; k++) {
+			if (s->queue[i] < MAX_TASKS) {
+				wakeup_task(s->queue[i]);
+				s->queue[i] = MAX_TASKS;
+				break;
+			}
+			i = (i + 1) % MAX_TASKS;
+		}
+		spinlock_unlock(&s->lock);
+	}
+
+	return 0;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/include/metalsvm/tasks.h b/include/metalsvm/tasks.h
index c88c8228..fb89eb77 100644
--- a/include/metalsvm/tasks.h
+++ b/include/metalsvm/tasks.h
@@ -36,6 +36,7 @@ int create_kernel_task(tid_t*, entry_point_t, void*, size_t);
 int join_kernel_task(tid_t);
 void schedule(void);
 task_t* get_new_task(void);
+int wakeup_task(tid_t);
 
 #ifdef __cplusplus
 }
diff --git a/kernel/main.c b/kernel/main.c
index eb57cdda..e45f5fef 100644
--- a/kernel/main.c
+++ b/kernel/main.c
@@ -25,8 +25,40 @@
 #include <metalsvm/mmu.h>
 #include <metalsvm/tasks.h>
 #include <metalsvm/processor.h>
+#include <metalsvm/semaphore.h>
 #include <asm/kb.h>
 
+static sem_t consuming, producing;
+static int val = 0;
+
+void* STDCALL producer(void* arg)
+{
+	int i;
+
+	for(i=0; i<5; i++) {
+		sem_wait(&producing);
+		kprintf("Produce value: current val %d\n", val);
+		val = 42;
+		sem_post(&consuming);
+	}
+
+	return NULL;
+}
+
+void* STDCALL consumer(void* arg)
+{
+	int i;
+
+	for(i=0; i<5; i++) {
+		sem_wait(&consuming);
+                kprintf("Consumer got %d\n", val);
+                val = 0;
+                sem_post(&producing);
+        }
+
+	return NULL;
+}
+
 void* STDCALL foo(void* arg)
 {
 	int i;
@@ -57,7 +89,7 @@ void* STDCALL join_test(void* arg)
 
 int main(void)
 {
-	tid_t id1, id2;
+	tid_t id1, id2, id3, id4;
 
 	system_init();
 	irq_init();
@@ -81,8 +113,13 @@ int main(void)
 
 	timer_set_frequency(TIMER_FREQ);
 
+	sem_init(&producing, 1);
+	sem_init(&consuming, 0);
+
 	create_kernel_task(&id1, foo, "Hello from foo1\n", 8192);
 	create_kernel_task(&id2, join_test, NULL, 0);
+	create_kernel_task(&id3, producer, NULL, 0);
+	create_kernel_task(&id4, consumer, NULL, 0);
 	current_task->idle = 1;
 	schedule();
 
diff --git a/kernel/tasks.c b/kernel/tasks.c
index 69514755..c5b9860e 100644
--- a/kernel/tasks.c
+++ b/kernel/tasks.c
@@ -149,6 +149,18 @@ out:
 	return ret;
 }
 
+int wakeup_task(tid_t id)
+{
+	if (task_table[id].status != TASK_BLOCKED) {
+		kprintf("Task %u is already unblocked\n", id);
+		return -1;
+	}
+
+	task_table[id].status = TASK_READY;
+	
+	return 0;
+}
+
 task_t* get_new_task(void) 
 {
 	unsigned int i, new_id;