// Very basic Karplus-Strong 

// based on this explanation http://sites.music.columbia.edu/cmc/MusicAndComputers/chapter4/04_09.php


#include <Adafruit_MCP4728.h>
#include <Wire.h>

Adafruit_MCP4728 mcp;

#define nsamp 256
#define dacmax 256

unsigned int phase;
unsigned int length;
unsigned int repeats;
int note = 0;
//int freqs[] = { 256, 228, 205, 192, 171, 154, 137, 128, 114, 102, 96, 85, 77, 68, 64 };
//int freqs[] = { 128, 114, 102, 96, 85, 77, 68, 64, 56, 51, 48, 42, 38, 34, 32 };
int freqs[] = { 64, 56, 51, 48, 42, 38, 34, 32, 28, 25, 24, 21, 19, 17, 16  };
int tune[] = { 0, 4, 3, 5, -1, -1, -1, -1 };

byte waveform[nsamp];

int pd = 30;

void setup() {

  cli();

//set timer1 interrupt at 1Hz
  TCCR1A = 0;// set entire TCCR1A register to 0
  TCCR1B = 0;// same for TCCR1B
  TCNT1  = 0;//initialize counter value to 0
  // set compare match register for 1hz increments
  //OCR1A = 15624;// = (16*10^6) / (1*1024) - 1 (must be <65536)
  //OCR1A = 7812;// = (16*10^6) / (1*1024) - 1 (must be <65536)
  OCR1A = 10000;
  // turn on CTC mode
  TCCR1B |= (1 << WGM12);
  // Set CS10 and CS12 bits for 1024 prescaler
  TCCR1B |= (1 << CS12) | (1 << CS10);  
  // enable timer compare interrupt
  TIMSK1 |= (1 << OCIE1A);

  sei();


  Serial.begin(115200);

  if (!mcp.begin(0x64)) {
    while (1) {
      delay(100);
    }
  }

  randomSeed(analogRead(A0));
  mcp.setSpeed(800000L);

  phase=0;
  note=0;
}

ISR(TIMER1_COMPA_vect){//timer1
  if( tune[note] > -1 ) {
    length=freqs[tune[note]];
    for (int i=0; i<nsamp; ++i){  
      waveform[i]=random(256);
    }
  }
  note++;
  if( note > 7 ) {
    note = 0;
  }
  pd = analogRead(A0) >> 4;
  Serial.println(pd);
}



void loop() {
  byte s1, s2;
  int p0 = phase;
  int p1 = phase - pd;
  if( p1 < 0 ) {
    p1 += length;
  } 
  phase += 1;
  if( phase >= length ) {
    phase = 0;
  }
  s1 = waveform[p1];
  s2 = waveform[p0];
  waveform[p0] =   ( s1 & s2 ) + ((s1 ^ s2) >> 1);
  mcp.fastWrite(s1 << 4, 0, 0, 0);
}