//waveform generator

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

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

Adafruit_MCP4728 mcp;

#define nsamp 256
#define dacmax 256

const byte nclk=42; //number of clock cycles of the loop
long int freq; //frequency in mHz
long unsigned int phase;
long unsigned int phase_inc;

void setup() {
  //TIMSK0 &= ~_BV(TOIE0); // disable timer0 overflow interrupt
 
  //Wire.setClock(1400000L); // wooooo
  Serial.begin(115200);
  while (!Serial)
    delay(10); // will pause Zero, Leonardo, etc until serial console opens


  // Try to initialize!
  if (!mcp.begin(0x64)) {
    Serial.println("Failed to find MCP4728 chip");
    while (1) {
      delay(10);
    }
  } else {
    Serial.println("Adafruit MCP4728 initialised");
  }


  freq=660;
  phase=0;
  calc_phase_inc();
  //phase_inc = 1;

  setwave();
}

const float pi=3.14159265;
byte waveform[nsamp];
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. 2^32/16E6=268.435456
void calc_phase_inc(){
  phase_inc=0.268435456*nclk*freq;
  Serial.println("phase inc");
  Serial.println(phase_inc);
}

//regular running: generate waves
void loop() {
  //phase+=900;
  //int redphase = phase >> 24;
  phase += analogRead(A0);
  int redphase = phase % nsamp;
  mcp.fastWrite(waveform[redphase] << 4, 0, 0,   0);
}