Arduino-Pedal-Effects/c/clean_ring_buffer.ino

// RING BUFFER CLEAN
// via www.Electrosmash.com
// via OpenMusicLabs

//defining hardware resources.
#define LED 13
#define FOOTSWITCH 12
#define TOGGLE 2
#define PUSHBUTTON_1 A5
#define PUSHBUTTON_2 A4

//defining the output PWM parameters
#define PWM_FREQ 0x00FF // pwm frequency - 31.3KHz
#define PWM_MODE 0 // Fast (1) or Phase Correct (0)
#define PWM_QTY 2 // 2 PWMs in parallel
#define BUFF_SIZE 500 // size of ring buffer, can theoretically be anything
                      // 500 should hold 15.9 ms of audio

// STRUCTURES

// can be used to implement a virtual debounce, e.g.
// if (millis() - button_time_s.pb1 > 250)
// {
//    do something
//    button_time_s.pb1 = millis();
// }
// {
//    don't do something as it will be the same press as before
// }
// also keeps track of when the footswitch is turned on
struct button_time_s
{
  long footswitch;
  long pb1;
  long pb2;
};

// counts iterations of main and interrupt loops
struct count_s
{
  int main;
  int interrupt;
};

// keeps track of when the footswitch is turned on
// by storing a current and an old
// if current != old
// switch has just been turned on
struct switch_flag_s
{
  bool current;
  bool old;
};

// ring buffer structure
// buff is array to store the audio
// head and tail and head and tail, respectively
struct ring_buff_s
{
  int buff[BUFF_SIZE];
  int head;
  int tail;
};

// VARIABLES
int input, vol_variable=512;
byte ADC_low, ADC_high;
int offset = 5;  //offset of 5 ms will still be "real time", can theoretically have up to 30 ms delay between input and output and still appear "real time"
long milli;
button_time_s button_time;
count_s count;
switch_flag_s switch_flag;
ring_buff_s buf;

// BUFFER FUNCTIONS
void push_to_buff(int in)
{
  buf.buff[buf.head] = in;
  buf.head++;
  if (buf.head == BUFF_SIZE)
  {
    buf.head = 0;
  }
}

int pop_from_buff (void)
{
  int out = buf.buff[buf.tail];
  if (buf.tail != buf.head)
  {
    buf.tail++;
  }
  if (buf.tail == BUFF_SIZE)
  {
    buf.tail = 0;
  }
  return out;
}

void setup()
{
  //setup IO
  pinMode(FOOTSWITCH, INPUT_PULLUP);
  pinMode(PUSHBUTTON_1, INPUT_PULLUP);
  pinMode(PUSHBUTTON_2, INPUT_PULLUP);
  pinMode(LED, OUTPUT);

  // setup ADC
  ADMUX = 0x60; // left adjust, adc0, internal vcc
  ADCSRA = 0xe5; // turn on adc, ck/32, auto trigger
  ADCSRB = 0x07; // t1 capture for trigger
  DIDR0 = 0x01; // turn off digital inputs for adc0

  // setup PWM
  TCCR1A = (((PWM_QTY - 1) << 5) | 0x80 | (PWM_MODE << 1)); //
  TCCR1B = ((PWM_MODE << 3) | 0x11); // ck/1
  TIMSK1 = 0x20; // interrupt on capture interrupt
  ICR1H = (PWM_FREQ >> 8);
  ICR1L = (PWM_FREQ & 0xff);
  DDRB |= ((PWM_QTY << 1) | 0x02); // turn on outputs
  sei(); // turn on interrupts - not really necessary with arduino
}


// MAIN LOOP
// checks the footswitch is pushed every 100 loops
// changes the switch_flag.current
// checks if the footswitch has been recently pressed
// if switch flag is true call functions
// else just set LED here,
// doesn't need to optimised if no audio is being processed
// finally, increment count
void loop()
{
  if (count.main % 100 == 0)
  {
    switch_flag.current = digitalRead(FOOTSWITCH);
    if (switch_flag.current != switch_flag.old)
    {
      button_time.footswitch = millis();
      digitalWrite(LED, true);
    }
    switch_flag.old = switch_flag.current;
    if (switch_flag.current == true)
    {
      milli = millis();
      // add code here when effect is on
    }
    else
    {
      digitalWrite(LED, false);
    }
  }
  count.main++;
}

// AUDIO INPUTTER
// pulls the audio from the ADC
// pushes it to the ring buffer
void audio_inputter()
{
  ADC_low = ADCL; // you need to fetch the low byte first
  ADC_high = ADCH;
  input = ((ADC_high << 8) | ADC_low); // make a signed 16b value
  if (input > 0x8000)
  {
    input = input + 0x8000;
  }
  push_to_buff(input);
}

// AUDIO OUTPUTTER
// wait until
// pop audio from ring buffer and output to PWM
void audio_outputter()
{
  if (milli - button_time.footswitch > offset)
  {
    int output = pop_from_buff();
    OCR1AL = ((output + 0x8000) >> 8); // convert to unsigned, send out high byte
    OCR1BL = output; // send out low byt
  }
}

// TIMER1 INTERRUPT
// checks the switch flag is true
// inputs then outputs audio
// increment count
ISR(TIMER1_CAPT_vect)
{
  if (switch_flag.current == true)
  {
    audio_inputter();
    audio_outputter();
    count.interrupt++;
  }
}