diff --git a/lambda-test/lambda-test.c b/lambda-test/lambda-test.c
index 5b435d7..ef3d450 100644
--- a/lambda-test/lambda-test.c
+++ b/lambda-test/lambda-test.c
@@ -44,14 +44,19 @@
 	// test that the pull-up resistor for the mouton is enabled
 	assertTrue(bit_is_set(PORTB, PB0));
 
+	// test that the beep output pin is enabled
+	assertTrue(bit_is_set(DDRB, PB1));
+
 	return true;
 }
 
 bool testSetupSleepMode(void) {
 	setupSleepMode();
 
-	// set_sleep_mode(SLEEP_MODE_ADC);
-	assertTrue(bit_is_set(SMCR, SM0));
+	// set_sleep_mode(SLEEP_MODE_IDLE);
+	assertFalse(bit_is_set(SMCR, SM2));
+	assertFalse(bit_is_set(SMCR, SM1));
+	assertFalse(bit_is_set(SMCR, SM0));
 
 	return true;
 }
@@ -66,6 +71,9 @@
 	// assertTrue(bit_is_set(PCMSK0, PB0));
 	// enable timer 0 overflow interrupt
 	assertTrue(bit_is_set(TIMSK0, TOIE0));
+	// USART RX complete interrupt 0 enabled
+	assertTrue(bit_is_set(UCSR0B, RXCIE0));
+
 	// sei(); // enable global interrupts
 	assertTrue(bit_is_set(SREG, SREG_I));
 
@@ -75,10 +83,19 @@
 bool testInitTimers(void) {
 	initInterrupts();
 
-	// timer clock prescaler /64 = 15.625 kHz overflowing every 16.2 ms
+	// timer0 clock prescaler /64 = 15.625 kHz overflowing every 16.2 ms
 	uint8_t prescalerBy64 = (1 << CS00) | (1 << CS01);
 	assertTrue((TCCR0B & prescalerBy64) == prescalerBy64);
 
+	// timer1 CTC mode, TOP OCR1A
+	assertTrue(bit_is_set(TCCR1B, WGM12));
+	// timer clock prescaler/8
+	assertTrue(bit_is_set(TCCR1B, CS11));
+	// toggles PB1 at 7.8 kHz generating a 3.9 kHz beep
+	// assertTrue(OCR1A == 16);
+	// less noisy 1.8 kHz
+	assertTrue(OCR1A == 32);
+
 	return true;
 }
 
diff --git a/lambda/interrupts.c b/lambda/interrupts.c
index 50f009a..0a902c0 100644
--- a/lambda/interrupts.c
+++ b/lambda/interrupts.c
@@ -30,7 +30,7 @@
 	// enable timer 0 overflow interrupt
 	TIMSK0 |= (1 << TOIE0);
 
-	// enable RC complete interrupt 0
+	// enable USART RX complete interrupt 0
 	UCSR0B |= (1 << RXCIE0);
 	// enable data register empty interrupt 0
 	// UCSR0B |= (1 << UDRIE0);
diff --git a/lambda/lambda.c b/lambda/lambda.c
index 4c0ca1c..570cd3a 100644
--- a/lambda/lambda.c
+++ b/lambda/lambda.c
@@ -53,6 +53,9 @@
 	}
 }
 
+/**
+ * Called when data was received via USART.
+ */
 ISR(USART_RX_vect) {
 	if (bit_is_set(UCSR0A, RXC0) && ! usartReceived) {
 		char data = UDR0;