//waveform generator

// hacked from https://www.instructables.com/Arduino-Waveform-Generator-1/

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

Adafruit_MCP4728 mcp;

#define nsamp 32
#define dacmax 256

const byte nclk = 200; // a guess
long int freq; //frequency in Hz
long unsigned int phase;
long unsigned int phase_inc;

void setup() {
  TIMSK0 &= ~_BV(TOIE0); // disable timer0 overflow interrupt

//  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)
//   // 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);
    }
  }

//  mcp.setSpeed(400000L);
//  mcp.setSpeed(800000L);
  mcp.setSpeed(800000L);

  freq=440;
  phase=0;
  calc_phase_inc();

  setwave();
}

const float pi=3.14159265;
byte waveform[nsamp];
byte phaseb = 0;
void setwave(){
  for (int isamp=0; isamp<nsamp; ++isamp){
    float phip=(isamp+0.5)/nsamp;
    float phi=2*pi*phip;
    int val=0;

    //saw
    //val = dacmax * isamp / nsamp;
    //val = ( isamp < nsamp / 2 ) ? 0 : dacmax - 1;
        //sine
    val=(sin(phi)+1.0)*dacmax/2;
    //val=((sin(phi)+0.333*sin(3*phi))/0.943+1)*dacmax/2;
    // val=max(val,0);
    // val=min(val,dacmax-1);
    waveform[isamp]=val;
  }
}


//calculate the phase increment. 
void calc_phase_inc(){
  // by measurement, 2^27 is about 138Hz (C below middle C)
  // 2^27 / 138 = 972592.231884058
  phase_inc = freq * 975592.231884058;
}

// ISR(TIMER1_COMPA_vect){//timer1 interrupt 1Hz 
//   freq = 55 + 1760.0 * analogRead(A0) / 1024.0;
//   Serial.println(freq);
//   calc_phase_inc();
// }
 


void loop() {
  phase += phase_inc;
  int redphase = phase >> 27;
  freq = 55 + 1760.0 * analogRead(A0) / 1024.0;
  calc_phase_inc();
  mcp.fastWrite(waveform[redphase] << 4, 0, 0, 0);
}