adc_freerunner.cpp

#include "adc_freerunner.h"

#include <avr/interrupt.h> 

uint16_t volatile adc_values[ADC_CHANNELS];

void setup_adc(){
   ADCSRA |= (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0); // Set ADC prescaler to 128 - 125KHz sample rate @ 16MHz

   ADMUX |= (1 << REFS0); // Set ADC reference to AVCC
//   ADMUX |= (1 << ADLAR); // Left adjust ADC result to allow easy 8 bit reading

//   ADCSRA |= (1 << ADFR);  // Set ADC to Free-Running Mode
   ADCSRA |= (1 << ADATE);

   ADCSRA |= (1 << ADEN);  // Enable ADC
   ADCSRA |= (1 << ADSC);  // Start A2D Conversions

   // enable ADC interrupt
   ADCSRA |= (1 << ADIE);

   // start interrupts
//    sei(); 
}

ISR(ADC_vect) {
  static uint8_t oldchan;
  static uint8_t counter;
  static uint16_t adc_buffer[ADC_CHANNELS];
  uint8_t curchan = ADMUX & 7;
  adc_buffer[oldchan] += ADCL | (ADCH << 8);
  oldchan = curchan;
  if(++curchan == ADC_CHANNELS){
    curchan = 0;
    if(++counter == ADC_OVERSAMPLING){
      counter = 0;
      for(uint8_t i=0; i<ADC_CHANNELS; ++i){
	adc_values[i] = adc_buffer[i];
	adc_buffer[i] = 0;
      }
    }
  }
  ADMUX = (ADMUX & ~7) | curchan;
}