54,  55,  56,  57,  59,  60,  61,  63,  64,  66,  67,  68,  70,  71,  72,  74,  75,  77,  78,  80,  81, 

   83,  84,  86,  87,  88,  90,  91,  93,  95,  96,  98,  99, 101, 102, 104, 105, 107, 108, 110, 111, 113, 

  115, 116, 118, 119, 121, 122, 124, 125

};

inline uint8_t afsk_read_sample(int phase)

{

  return pgm_read_byte_near(afsk_sine_table + phase);

}

volatile uint16_t phase = 10;

volatile uint16_t phasedelta = 3300;

extern const uint16_t TABLE_SIZE = sizeof(afsk_sine_table);

void afsk_setup() {

  // Source timer2 from clkIO (datasheet p.164)

  ASSR &= ~(_BV(EXCLK) | _BV(AS2));

  // Set fast PWM mode with TOP = 0xff: WGM22:0 = 3  (p.150)

  TCCR2A |= _BV(WGM21) | _BV(WGM20);

  TCCR2B &= ~_BV(WGM22);

  // Do non-inverting PWM on pin OC2B (arduino pin 3) (p.159).

  // OC2A (arduino pin 11) stays in normal port operation:

  // COM2B1=1, COM2B0=0, COM2A1=0, COM2A0=0

  TCCR2A = (TCCR2A | _BV(COM2B1)) & ~(_BV(COM2B0) | _BV(COM2A1) | _BV(COM2A0));

  // No prescaler (p.162)

  TCCR2B = (TCCR2B & ~(_BV(CS22) | _BV(CS21))) | _BV(CS20);

  // Enable interrupt when TCNT2 reaches TOP (0xFF) (p.151, 163)

	//TIMSK2 |= _BV(TOIE2);

	TIMSK2 |= 0b00000001;

	// Initialize PORTA

	DDRA = 0xff;

	PORTA = 0x00;

	DDRD = 0xff;

	PORTD = 0xff;

	// todo: init radio, maybe in main

	sei();

}

void afsk_test() {	

	afsk_start();

	while(afsk_busy());

	_delay_ms(500);

}

// constants

#define MODEM_CLOCK_RATE F_CPU

#define PLAYBACK_RATE MODEM_CLOCK_RATE / 256  // Fast PWM

#define BAUD_RATE 1200

//#define SAMPLES_PER_BAUD PLAYBACK_RATE / BAUD_RATE // = 36

#define SAMPLES_PER_BAUD 36

// phase offset of 1800 gives ~1900 Hz

// phase offset of 3300 gives ~2200 Hz

#define PHASE_DELTA_1200 1800

#define PHASE_DELTA_2200 2200

// Module globals

volatile unsigned char current_byte;

volatile unsigned char current_sample_in_baud;    // 1 bit = SAMPLES_PER_BAUD samples

volatile bool go = false;                 

volatile unsigned int packet_pos;                 // Next bit to be sent out

volatile unsigned int afsk_packet_size = 10;

volatile const uint8_t *afsk_packet;

void afsk_send(const uint8_t *buffer, int len)

{

	afsk_packet_size = len;

	afsk_packet = buffer;

}

int afsk_busy()

{

	return go;

}

void afsk_start()

{

	phasedelta = PHASE_DELTA_1200;

	phase = 0;

	packet_pos = 0;

	current_sample_in_baud = 0;

	go = true;

	// Key the radio

	afsk_ptt_on();

	// Start transmission

	afsk_timer_start();

}

afsk_ptt_off() {

}

afsk_ptt_on() {

}

ISR(TIMER2_OVF_vect) 

{

	if (go) {

		// If done sending packet

		if (packet_pos == afsk_packet_size) {

			go = false;         // End of transmission

			afsk_timer_stop();  // Disable modem

			afsk_ptt_off();    // Release PTT

			return; // done

		}

		// If sent SAMPLES_PER_BAUD already, go to the next bit

		if (current_sample_in_baud == 0) {    // Load up next bit

			if ((packet_pos & 7) == 0) {          // Load up next byte

				current_byte = afsk_packet[packet_pos >> 3];

			}				

			else {

				current_byte = current_byte / 2;  // ">>1" forces int conversion

			}			

			if ((current_byte & 1) == 0) {

				// Toggle tone (1200 <> 2200)

				phasedelta ^= (PHASE_DELTA_1200 ^ PHASE_DELTA_2200);

			}

		}

		phase += phasedelta;

		uint8_t s = afsk_read_sample((phase >> 7) & (TABLE_SIZE - 1));

		afsk_output_sample(s);

		if(++current_sample_in_baud == SAMPLES_PER_BAUD) {

			// sounds fun when this is commented out... but why??!?!

			packet_pos++;

		}

	}

}	

void afsk_output_sample(uint8_t s) {

	OCR2B = s;

}

void afsk_timer_start()

{

	// Clear the overflow flag, so that the interrupt doesn't go off

	// immediately and overrun the next one (p.163).

	TIFR2 |= _BV(TOV2);       // Yeah, writing a 1 clears the flag.

	// Enable interrupt when TCNT2 reaches TOP (0xFF) (p.151, 163)

	TIMSK2 |= _BV(TOIE2);

}

void afsk_timer_stop()

{

	// Resting duty cycle

	// Output 0v (could be 255/2, which is 0v after coupling... doesn't really matter)

	// Disable playback interrupt

	TIMSK2 &= ~_BV(TOIE2);

}