// based on https://wokwi.com/projects/330112801381024338
// for https://forum.arduino.cc/t/oversampled-adc-pwm-synchronization-for-my-ball-on-beam-project-at-high-frequency-on-my-arduino-uno/1084814/18


volatile uint16_t AnalogReadings;               // Wanted 10 bit value as a variable
const byte InputPin = A0;                       // Input 8-bit Voltage signal at A0
 

ISR(ADC_vect)                              
{
   while(ADCSRA & (1<<ADSC));              // wait for conversion
   ADC = (ADCL | (ADCH << 8));            // Bit shifting for 10-bit resolution from 8-bit
   AnalogReadings = ADC;                          
} 

ISR(TIMER1_COMPA_vect)                   
{
  AnalogReadings = ADC;                          
  ADCSRA |= (1<<ADSC);                    // Start the next conversion
}

ISR(Timer1_COMPB_vect)                   
{ 
  AnalogReadings = ADC;                          
  ADCSRA |= (1<<ADSC);                   // Start the next conversion 
}

ISR(TIMER1_OVF_vect)                     
{
  AnalogReadings = ADC;                          
  TCNT1 = 0;                             // TCNT1 set to initialise again; maybe not needed as TCNT starts by itself
  ADCSRA |= (1<<ADSC);                   // Event the conversion start
}

void setup()
  {
  Serial.begin(115200); // set baudrate

  //CONFIGURE ADC
  cli();                                 //disable all interrupts
  ADCSRA = 0;                  
  ADCSRB= 0;                            // Initialize ADC 
  ADMUX = 0;
  
  // Enable Input channel A0;
  ADMUX |= (1<<ADLAR);                                 // (1<<ADLAR) for bit shifting for 8-10 bit conversion
  ADMUX &= (ADMUX & 0xF8) | (InputPin);              // AREF; so not bit to set
  
  ADCSRA |= (1<<ADEN);                      
  ADCSRA |= (1<<ADIF);                 // enable interrupt flag
  ADCSRA |= (1<<ADIE);                 // enable interrupts 
  sei();                               // enable global interrupts
  ADCSRA |= (1<<ADPS2);                     // Prescalar of 16;  16MHz/ 16 = 1MHz/13 clock cycles= ~76Khz (ADC Sampling rate) = ~13 uS (one conversion period) 
  ADCSRB |= (1<<ADTS2) | (1<<ADTS0);        // 
 
  ADCSRA |= (1<<ADSC);                       // Start the first conversion
  while (ADCSRA & (1<<ADSC));                   //wait for the completion of ADC conversion
   
  cli();                               // disable interrupts                                                                               
  // Timer  Settings
  TCCR1A  = 0;
  TCCR1B  = 0;                             // Initialise timer1
  TCNT1   = 0;

  // choose phase and frequency correct PWM, TOP defined by ICR1
  TCCR1A  |= (1<<COM1A0) | (1<<COM1A1);                                   // toggle outputs OC1A and OC1B
  TCCR1A |= (1<<COM1B1);                                                  // OC1A should be logical negated to OC1B
  TCCR1B  |= (0b101<<CS10) | (1<<WGM13);                                       // choose PWM mode (see above) and set prescaler to 1
   // TCCR1B https://onlinedocs.microchip.com/pr/GUID-80B1922D-872B-40C8-A8A5-0CBE009FD908-en-US-3/index.html?GUID-07C6751D-0319-41A4-AC9F-9B0AFDA21A07
   // prescaler /1024 for slower output
  ICR1 = 255;                                                            // set TOP value to 255 --> resulting PWM-frequency = 16MHz / (2 * 1 * 255) = 31.372kHz = 32uS ;one pwm period
  OCR1A   = 128;                                                         //Duty cyycle 50%
  OCR1B   = 128;                                                         // for both signals    

  TIMSK1  |= (1<<OCIE1A)| (1<<OCIE1B) |(1<<TOIE1);                       // set 2 compare match interrupt & 1 overflow event masks 
  TIFR1 |= (1<<OCF1A)| (1<<OCF1B) |(1<<TOV1);                            // may not be needed as the flag is reset when the interrupt vector is initiated    
                           
  sei();                                        // enable interrupts again  

  DDRB |= (1<<PB1) | (1<<PB2);                                  // Enable output ports 9&10 digital PWM pin

  ADCSRA |= (1<<ADATE);   
  Serial.println("Setup Complete");
                                       // enable auto triggering mode
}

void loop()
{
 while(1) 
 {
  while(ADCSRA & ~(ADSC));

  if(TIMSK1 & ~(1<<OCF1A))
   {
     Serial.println(AnalogReadings);
     Serial.flush();
   }
  else if(TIMSK1 & ~(1<<OCF1B))
   {
     Serial.println(AnalogReadings);
     Serial.flush();
   }
  else if(TIMSK1 & ~(1<<TOV1))
   {
     Serial.println(AnalogReadings);
     Serial.flush();
   }
  } 
}