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/*
karplus.pde
guest openmusiclabs 4.3.12
*/


// setup codec parameters
// must be done before #includes
// see readme file in libraries folder for explanations
#define SAMPLE_RATE 44 // 44.1Khz
#define ADCS 1 // no ADCs are being used

// include necessary libraries
#include <Wire.h>
#include <SPI.h>
#include <AudioCodec.h>

// create data variables for audio transfer
int left_in = 0x0000;
int left_out = 0x0000;
int right_in = 0x0000;
int right_out = 0x0000;
int last_value = 0x0000;
int curr_value = 0x0000;
unsigned int decay = 0x0000;
#define DECAY 65000
unsigned int mod0_value =0;

// create a delay buffer in memory
#define SIZE 800 // buffer size is limited by microcontroller SRAM size
int delaymem[SIZE]; // 800 positions x 2 bytes = 1600 bytes of SRAM
unsigned int location = 0; // buffer location to read/write from
unsigned int boundary = SIZE;

void setup() {
  
  for (int i = 0; i < SIZE; i++) {
    delaymem[i] = random(65535);
  }
  
  AudioCodec_init(); // setup codec registers
  // call this last if setting up other parts
}

void loop() {
  while (1); // reduces clock jitter
}

// timer1 interrupt routine - all data processed here
ISR(TIMER1_COMPA_vect, ISR_NAKED) { // dont store any registers

  // &'s are necessary on data_in variables
  AudioCodec_data(&left_in, &right_in, left_out, right_out);
  
   // & is required before adc variable
  AudioCodec_ADC(&mod0_value);
  
  if (decay++ < DECAY) {
  
    delaymem[location++] = left_out;
    // check if location has gotten bigger than buffer size
    if (location >= boundary) {
      location = 0; // reset location
    }
    curr_value = delaymem[location];
    left_out = (last_value>>1) + (curr_value>>1);
    last_value = curr_value;
    }
  else {
    for (int i = 0; i < SIZE; i++) {
      delaymem[i] = random(65535);
    }
    decay = 0;
    
    unsigned int scale = SIZE;
    MultiU16X16toH16(boundary, mod0_value, scale);
  }
  // dont forget to return from interrupt
  reti();
}