diff --git a/firmware/include/pentabug/hal.h b/firmware/include/pentabug/hal.h
index 919591c..622186b 100644
--- a/firmware/include/pentabug/hal.h
+++ b/firmware/include/pentabug/hal.h
@@ -42,6 +42,13 @@ void motor_on(void);
 void motor_off(void);
 void motor_inv(void);
 
+// BUZZER
+
+void buzzer_up(void);
+void buzzer_down(void);
+void buzzer_inv(void);
+void buzzer_off(void);
+
 // WAITING
 
 // waits the given amount of ms
diff --git a/firmware/lib/hal.c b/firmware/lib/hal.c
index 932a6a1..0315023 100644
--- a/firmware/lib/hal.c
+++ b/firmware/lib/hal.c
@@ -19,17 +19,21 @@ inline static void major_interrupt(void) {
 	uint8_t i = 0;
 
 	for(i = 0; i < 2; ++i) {
+		// button pressed?
 		if(PINB & (1 << i)) {
-			if(button_count[i] && button_count[i] > 10 && button_count[i] < 200) {
+			// pressed for more than 50ms is a click
+			if(button_count[i] > 10 && button_count[i] < 200) {
 				button_pressed[i] = 1;
 			}
 
+			// not pressed, reset
 			button_count[i] = 0;
 		} else {
+			//.count time pressed
 			++button_count[i];
 		}
 
-		// 1s pressed
+		// 1s pressed, request next app
 		if(button_count[i] == 200) {
 			next_app(i ? 1 : -1);
 		}
@@ -38,10 +42,14 @@ inline static void major_interrupt(void) {
 
 // WARNING: this interrupt is already way too big. extend only in case of emergency!
 ISR(TIMER0_COMPA_vect) {
+	// generate 38kHz signal
+
 	if(ir_active) {
 		PORTD ^= 1 << 2;
 	}
 
+	// call button handling less often
+
 	++int_skip;
 
 	if(int_skip >= 64 * 5) {
@@ -49,6 +57,8 @@ ISR(TIMER0_COMPA_vect) {
 		major_interrupt();
 	}
 
+	// tell wait_ms() that 1/38 ms has passed
+
 	--wait_time;
 }
 
@@ -68,6 +78,8 @@ void init_hw(void) {
 	TCCR0A = (1 << WGM01);
 	TCCR0B = (1 << CS00);
 
+	// activate interrupts
+
 	sei();
 }
 
@@ -164,10 +176,32 @@ void motor_inv(void) {
 	PORTB ^= 1 << 6;
 }
 
+void buzzer_up(void) {
+	PORTB |= 1 << 7;
+	PORTC &= ~(1 << 0);
+}
+
+void buzzer_down(void) {
+	PORTB &= ~(1 << 7);
+	PORTC |= 1 << 0;
+}
+
+void buzzer_inv(void) {
+	PORTB ^= 1 << 7;
+	PORTC ^= 1 << 0;
+}
+
+void buzzer_off(void) {
+	PORTB &= ~(1 << 7);
+	PORTC &= ~(1 << 0);
+}
+
 void wait_ms(uint16_t ms) {
 	// TODO: this function seems to be ~10% too fast
 	int32_t cycles = ms * (int32_t)64;
 
+	// wait_time is int16_t for performance reasons, so we have to wait multiple times
+
 	while(cycles >= INT16_MAX) {
 		cycles -= INT16_MAX;
 		wait_time = INT16_MAX;
@@ -177,6 +211,8 @@ void wait_ms(uint16_t ms) {
 		}
 	}
 
+	// wait the odd time left
+
 	wait_time = cycles;
 
 	while(wait_time > 0) {
diff --git a/firmware/lib/music.c b/firmware/lib/music.c
index 8cc5002..7f72ccf 100644
--- a/firmware/lib/music.c
+++ b/firmware/lib/music.c
@@ -7,18 +7,20 @@
 #include <pentabug/hal.h>
 
 static void tune(void) {
-	PORTB ^= 1 << 7;
+	buzzer_inv();
 }
 
 void set_note(uint16_t note, uint8_t octave) {
 	if(note != NOTE_PAUSE) {
+		buzzer_up();
 		start_timer(PRESCALE_8, note >> octave, tune);
 	} else {
-		stop_timer();
+		stop_note();
 	}
 }
 
 void stop_note(void) {
+	buzzer_off();
 	stop_timer();
 }