diff --git a/Makefile b/Makefile
index 45e656c..03db139 100644
--- a/Makefile
+++ b/Makefile
@@ -35,6 +35,8 @@ OBJS+= usartu.o
 OBJS+= scheduler.o
 OBJS+= atomic.o
 OBJS+= semaphore.o
+OBJS+= mutex.o
+
 
 main.elf: $(OBJS)
 	$(TARGET)-gcc $(^F) $(LDFLAGS) -o $@
diff --git a/atomic.S b/atomic.S
index 4f72bd6..cc67731 100644
--- a/atomic.S
+++ b/atomic.S
@@ -3,10 +3,10 @@
 
 .text
 
-.globl  atom_inc32
-.type   atom_inc32, %function
+.globl  atomic_inc32
+.type   atomic_inc32, %function
 
-atom_inc32:
+atomic_inc32:
 1:      ldrex           r2, [r0]
         add             r2, r2, r1
         strex           r3, r2, [r0]
@@ -16,10 +16,10 @@ atom_inc32:
         bx              lr
 
 
-.globl  atom_dec32
-.type   atom_dec32, %function
+.globl  atomic_dec32
+.type   atomic_dec32, %function
 
-atom_dec32:
+atomic_dec32:
 2:      ldrex           r2, [r0]
         sub             r2, r2, r1
         strex           r3, r2, [r0]
diff --git a/atomic.h b/atomic.h
index 90563eb..2cd54c3 100644
--- a/atomic.h
+++ b/atomic.h
@@ -7,7 +7,7 @@
 
 #include <stdint.h>
 
-int32_t atom_inc32(volatile int32_t *addr, int32_t value);
-int32_t atom_dec32(volatile int32_t *addr, int32_t value);
+int32_t atomic_inc32(volatile int32_t *addr, int32_t value);
+int32_t atomic_dec32(volatile int32_t *addr, int32_t value);
 
 #endif
diff --git a/main.c b/main.c
index 3fcffdc..0f7a993 100644
--- a/main.c
+++ b/main.c
@@ -92,7 +92,7 @@ void task3(void) {
 void task4(void) {
     static volatile int32_t t4;
     while (true) {
-        atom_inc32(&t4, (int32_t)1);
+        atomic_inc32(&t4, (int32_t)1);
         sem_wait(&g_sem);
         printf("task 4 %d %lu\r\n", g_uptime, t4);
         sem_post(&g_sem);
diff --git a/mutex.c b/mutex.c
new file mode 100644
index 0000000..6a87ea3
--- /dev/null
+++ b/mutex.c
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2022 Oleg Borodin  <borodin@unix7.org>
+ */
+
+#include "mutex.h"
+#include "atomic.h"
+
+void mutex_init(mutex_t* mutex) {
+    mutex->value = 1;
+}
+
+int32_t mutex_wait(mutex_t* mutex) {
+    //while(mutex->value <= 0);
+    //mutex->value--;
+    //return mutex->value;
+    while (atomic_dec32(&(mutex->value), (int32_t)0) <= 0);
+    return atomic_dec32(&(mutex->value), (int32_t)1);
+}
+
+int32_t mutex_post(mutex_t* mutex) {
+    //mutex->value++;
+    //return mutex->value;
+    return atomic_inc32(&(mutex->value), (int32_t)1);
+}
diff --git a/mutex.h b/mutex.h
new file mode 100644
index 0000000..6c3e03d
--- /dev/null
+++ b/mutex.h
@@ -0,0 +1,14 @@
+/*
+ * Copyright 2022 Oleg Borodin  <borodin@unix7.org>
+ */
+
+
+#include <stdint.h>
+
+typedef struct {
+    int32_t value;
+} mutex_t;
+
+void mutex_init(mutex_t* mutex);
+int32_t mutex_wait(mutex_t* mutex);
+int32_t mutex_post(mutex_t* mutex);
diff --git a/semaphore.c b/semaphore.c
index c8edee4..5cd116b 100644
--- a/semaphore.c
+++ b/semaphore.c
@@ -13,12 +13,12 @@ int32_t sem_wait(sem_t* sem) {
     //while(sem->value <= 0);
     //sem->value--;
     //return sem->value;
-    while (atom_dec32(&(sem->value), (int32_t)0) <= 0);
-    return atom_dec32(&(sem->value), (int32_t)1);
+    while (atomic_dec32(&(sem->value), (int32_t)0) <= 0);
+    return atomic_dec32(&(sem->value), (int32_t)1);
 }
 
 int32_t sem_post(sem_t* sem) {
     //sem->value++;
     //return sem->value;
-    return atom_inc32(&(sem->value), (int32_t)1);
+    return atomic_inc32(&(sem->value), (int32_t)1);
 }