diff --git a/include/sound4calc.h b/include/sound4calc.h
index c9d213c..73ee0a1 100644
--- a/include/sound4calc.h
+++ b/include/sound4calc.h
@@ -1,14 +1,15 @@
 #ifndef _SOUND4CALC_H
     #define _SOUND4CALC_H
 
-extern char wave_signal[25]; // simple waveform*
-extern unsigned short duration; // equivalent as 2000 ms duration sound
+extern char wave_signal[25];
+extern unsigned short duration;
 extern unsigned int freq;
 
 void CallSequence();
 void PutPinState(char level);
 void PlayNote();
 void InitPorts();
+void StopTimer();
 
 //SH4 addresses
 #define	SH7305_PJCR 0xA4050110
diff --git a/src/main.c b/src/main.c
index 7aa12c1..7b5b4fc 100644
--- a/src/main.c
+++ b/src/main.c
@@ -44,7 +44,7 @@ int main(void)
             case KEY_F2 : CallSequence(); break;
 
             case KEY_EXIT :
-                timer_stop(TIMER_USER);
+                StopTimer();
                     return 1;
         }
     }
diff --git a/src/sound4calc.c b/src/sound4calc.c
index 78e4e3f..6a4b3fe 100644
--- a/src/sound4calc.c
+++ b/src/sound4calc.c
@@ -49,6 +49,10 @@ void CallNote()
     timer_start(TIMER_USER, freq * wavelength, Clock_Hz, PlayNote, freq * duration / 1000);
 }
 
+void StopTimer()
+{
+    timer_stop(TIMER_USER);
+}
 /*
   PlayNote()
   allow to make different waveforms with '-' and '_'