/*
 * fsk.c
 *
 * Created: 10/29/2012 7:40:34 PM
 *  Author: ethanzonca
 */

#define F_CPU 11059200

#include <stdint.h>
#include <stdbool.h>
#include <avr/io.h>
#include <avr/interrupt.h> 
#include <util/delay.h>
#include <avr/pgmspace.h>


PROGMEM extern const uint8_t afsk_sine_table[512] = {
  127, 129, 130, 132, 133, 135, 136, 138, 139, 141, 143, 144, 146, 147, 149, 150, 152, 153, 155, 156, 158, 
  159, 161, 163, 164, 166, 167, 168, 170, 171, 173, 174, 176, 177, 179, 180, 182, 183, 184, 186, 187, 188, 
  190, 191, 193, 194, 195, 197, 198, 199, 200, 202, 203, 204, 205, 207, 208, 209, 210, 211, 213, 214, 215, 
  216, 217, 218, 219, 220, 221, 223, 224, 225, 226, 227, 228, 228, 229, 230, 231, 232, 233, 234, 235, 236, 
  236, 237, 238, 239, 239, 240, 241, 242, 242, 243, 244, 244, 245, 245, 246, 247, 247, 248, 248, 249, 249, 
  249, 250, 250, 251, 251, 251, 252, 252, 252, 253, 253, 253, 253, 254, 254, 254, 254, 254, 254, 254, 254, 
  254, 254, 255, 254, 254, 254, 254, 254, 254, 254, 254, 254, 254, 253, 253, 253, 253, 252, 252, 252, 251, 
  251, 251, 250, 250, 249, 249, 249, 248, 248, 247, 247, 246, 245, 245, 244, 244, 243, 242, 242, 241, 240, 
  239, 239, 238, 237, 236, 236, 235, 234, 233, 232, 231, 230, 229, 228, 228, 227, 226, 225, 224, 223, 221, 
  220, 219, 218, 217, 216, 215, 214, 213, 211, 210, 209, 208, 207, 205, 204, 203, 202, 200, 199, 198, 197, 
  195, 194, 193, 191, 190, 188, 187, 186, 184, 183, 182, 180, 179, 177, 176, 174, 173, 171, 170, 168, 167, 
  166, 164, 163, 161, 159, 158, 156, 155, 153, 152, 150, 149, 147, 146, 144, 143, 141, 139, 138, 136, 135, 
  133, 132, 130, 129, 127, 125, 124, 122, 121, 119, 118, 116, 115, 113, 111, 110, 108, 107, 105, 104, 102, 
  101,  99,  98,  96,  95,  93,  91,  90,  88,  87,  86,  84,  83,  81,  80,  78,  77,  75,  74,  72,  71, 
   70,  68,  67,  66,  64,  63,  61,  60,  59,  57,  56,  55,  54,  52,  51,  50,  49,  47,  46,  45,  44, 
   43,  41,  40,  39,  38,  37,  36,  35,  34,  33,  31,  30,  29,  28,  27,  26,  26,  25,  24,  23,  22, 
   21,  20,  19,  18,  18,  17,  16,  15,  15,  14,  13,  12,  12,  11,  10,  10,   9,   9,   8,   7,   7, 
    6,   6,   5,   5,   5,   4,   4,   3,   3,   3,   2,   2,   2,   1,   1,   1,   1,   0,   0,   0,   0, 
    0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   1,   1,   1,   1, 
    2,   2,   2,   3,   3,   3,   4,   4,   5,   5,   5,   6,   6,   7,   7,   8,   9,   9,  10,  10,  11, 
   12,  12,  13,  14,  15,  15,  16,  17,  18,  18,  19,  20,  21,  22,  23,  24,  25,  26,  26,  27,  28, 
   29,  30,  31,  33,  34,  35,  36,  37,  38,  39,  40,  41,  43,  44,  45,  46,  47,  49,  50,  51,  52, 
   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
};

static 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);

// 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
#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_ptt_off() {
	// turn ptt off
}

void afsk_ptt_on() {
	// turn the ptt on... possibly delay based on spec
}







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??!?!
			current_sample_in_baud = 0;
			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)
	OCR2B = 0x80;

	// Disable playback interrupt
	TIMSK2 &= ~_BV(TOIE2);
}





// External

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();
}

int afsk_busy()
{
	return go;
}

void afsk_send(const uint8_t *buffer, int len)
{
	afsk_packet_size = len;
	afsk_packet = buffer;
}


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() {
	uint8_t flap[26] = {"abcdefghijklmnopqrstuvwxyz"};
	afsk_send(flap, sizeof(flap)*8);
	afsk_start();
	while(afsk_busy());
	_delay_ms(500);
}