char *note;
float freq = 0.0f;
int count_freq;

void MICROPHONE_init(void)
{
	/* start audio interrupts */
	MICROPHONE_DDR &= ~(1 << MICROPHONE_P);
	PCICR |= (1 << MICROPHONE_PCIE);
	MICROPHONE_PCMSK |= (1 << MICROPHONE_PCINT);
}

void TIMER1_init(void)
{
	/* set timer to one second, or one Hertz */
	TCCR1B |= (1 << CS12) | (1 << WGM12);
	TIMSK1 |= (1 << OCIE1A);
	OCR1A = 62500 - 1;
}

void TIMER1_free(void)
{
	TCCR1B = 0;
	TIMSK1 = 0;
	OCR1A = 0;
}

ISR(TIMER1_COMPA_vect)
{
	TIMER1_free();
	char buff[BUFF_SIZE];
	float f = count_freq;
	float df = freq - f;

	LCD_clear();
	LCD_printAt(LCD_FIRST_LINE_BEGIN, note);
	sprintf(buff, "%d", count_freq);
	LCD_printAt(LCD_SECOND_LINE_BEGIN, buff);
	if (fabsf(df) < FREQ_TOLERANCE) {
		/* note frequency is in tolerance interval */
		note = NULL;
		freq = 0.0f;
		_delay_ms(1000);
		LCD_clear();
		LCD_printAt(LCD_FIRST_LINE_BEGIN, note);
		LCD_printAt(LCD_SECOND_LINE_BEGIN, "OK");
		count_freq = 0;
	} else {
		/* tune note */
		if (f > FREQ_TOLERANCE)
			STEPPER_rotation(df);
		count_freq = 0;
		TIMER1_init();
	}
}

ISR(PCINT0_vect)
{
	/* count changes of sign in oscillation */
	if ((MICROPHONE_PIN & (1 << MICROPHONE_P)) == 0)
		count_freq++;
}