avr_piano/notes.c

/*
 *  EEL4746C - AVR Piano - Speaker Section
 *  speaker is connected to PD2 and ground
 *  15 buttons are connected to PD3-7, PC0-4, PB0-4
 *  the LCD Arduino UNO is connected to TX/RX (PD0/1)
 */

#include <avr/io.h>
#include <avr/interrupt.h>

#define	T1_PRESCALAR	8
#define FREQ(f)		(16e6 / f / T1_PRESCALAR / 2)

#define HIGH(sn)	((sn >> 8) & 0xff)
#define LOW(sn)		(sn & 0xff)

#define P_RX		0
#define P_TX		1
#define P_SPKR		2

unsigned short freqs[] = {
	// PD3-7
	FREQ(100),
	FREQ(200),
	FREQ(250),
	FREQ(300),
	FREQ(350),
	// PB0-4
	FREQ(400),
	FREQ(500),
	FREQ(600),
	FREQ(700),
	FREQ(750),
	// PC0-4
	FREQ(1000),
	FREQ(1250),
	FREQ(1500),
	FREQ(1750),
	FREQ(2000),

	[255] = 0	// used as a 'silent' note
};
unsigned char note = 0;

ISR (PCINT0_vect)
{
	// check if any button in the whole port is pressed
	for (unsigned char i = 0; i <= 5; i++) {
		if (PINB & (1 << i)) {
			note = i + 5;
			break;
		}
	}
}

ISR (PCINT1_vect)
{
	// check if any button in the whole port is pressed
	for (unsigned char i = 0; i <= 5; i++) {
		if (PINC & (1 << i)) {
			note = i + 10;
			break;
		}
	}
}

ISR (PCINT2_vect)
{
	// check if any button in the whole port is pressed
	for (unsigned char i = 3; i <= 7; i++) {
		if (PIND & (1 << i)) {
			note = i - 3;
			break;
		}
	}
}

void
usart_init(void)
{
	// 115200 bps, RX/TX enabled
	UBRR0 = 8;
	UCSR0B = (1 << RXEN0) | (1 << TXEN0);
	UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);
}

void
usart_send(unsigned char c)
{
	while (!(UCSR0A & (1 << UDRE0)));
	UDR0 = c;
}

unsigned char
usart_read(void)
{
	while (!(UCSR0A & (1 << RXC0)));
	return UDR0;
}

int
main(void) 
{
	// Data Direction for Buttons, UART, Speaker
	DDRB = 0x00;
	DDRC = 0x00;
	DDRD = (1 << P_TX) | (1 << P_SPKR); 

	// Enabling Pin Change Interrupt for All Buttons
	PCMSK0 = 0b00011111;
	PCMSK1 = 0b00011111;
	PCMSK2 = 0b11111000;
	PCICR = (1 << PCIE0) | (1 << PCIE1) | (1 << PCIE2);

	TCCR1A = 0x00; // use timer1 CTC mode
	TCCR1B = 1 << WGM12; // already prescaled by 8 in table

	sei();

	usart_init();

	// Sends Square wave to the Speaker When a Button is Pressed
	unsigned short cycles = 0;
	unsigned char last_note = 0;
	for (unsigned char n = 0;; n = (n + 1) % 2) {
		// check if any buttons are pressed, otherwise don't play a note
		if (((PINB & PCMSK0) | (PINC & PCMSK1) | (PIND & PCMSK2)) == 0) {
			// if a button was released, then send note and cycles played
			if (cycles > 0) {
				usart_send(last_note);
				usart_send(HIGH(cycles));
				usart_send(LOW(cycles));
				usart_send('\xff');
				cycles = 0;
			}
			continue;
		}

		// Prepare Timer/Counter
		TCNT1 = 1;
		last_note = note;
		OCR1A = freqs[note];
		TCCR1B |= 1 << CS11;

		while ((TIFR1 & (1 << OCF1A)) == 0); // Monitor OutPut Compare Flag

		// Toggles port For Speaker
		PORTD ^= 1 << P_SPKR;
		TIFR1 |= 1 << OCF1A;
		TCCR1B &= ~(1 << CS11);
		cycles = (cycles + 1) % 0xffff;
	}
}