Tooltron

#include "current.h"

#include <avr/io.h>

#include <avr/interrupt.h>

#include <math.h>

#define CYCLES_PER_SECOND 60 // wall power

#define SAMPLES_PER_CYCLE 10

#define N_SAMPLES 20

unsigned int samples[N_SAMPLES];

int sample_idx;

unsigned int sum;

unsigned long sum_sq;

void current_init() {

  /*

   * COM0A = 0, disconnect pin

   * WGM0 = 2, clear timer on compare

   */

  TCCR0A |= _BV(WGM01);

  /*

   * CS0 = 5, 1024 prescaler

   */

  TCCR0B |= _BV(CS02) | _BV(CS00);

  OCR0A = F_CPU / 1024 / SAMPLES_PER_CYCLE / CYCLES_PER_SECOND;

  /*

   * REFS = 0, Vcc reference (set to 2 for internal 1.1V reference)

   * MUX = 8, PB3(ADC8)

   */

  ADMUX = _BV(MUX3);

  /* TODO reduce power consumption with DIDR* */

  /*

   * ADLAR = 0, right adjust result

   * ADTS = 3, start on timer 0 compare match A

   */

  ADCSRB = _BV(ADTS1) | _BV(ADTS0);

  /*

   * ADEN = 1, enable

   * ADSC = 0, don't start yet

   * ADATE = 1, auto trigger

   * ADIE = 1, enable interrupt

   * ADPS = 4, prescale clock by 16

   */

  ADCSRA |= _BV(ADEN) | _BV(ADATE) | _BV(ADIE) | _BV(ADPS2);

}

ISR(ADC_vect) {

  unsigned int old, new;

  new = ADC;

  /* put sample into ring buffer */

  old = samples[sample_idx];

  samples[sample_idx++] = new;

  if (sample_idx == N_SAMPLES)

    sample_idx = 0;

  /* keep a running total of samples and samples squared */

  sum += new;

  sum -= old;

  sum_sq += new*new;

  sum_sq -= old*old;

}

/*unsigned char isqrt(unsigned int x) {

  unsigned int sqrt, mulmask;

  sqrt = 0;

  mulmask = 0x80;

  if (x > 0) {

    while (mulmask) {

      sqrt |= mulmask;

      if (sqrt * sqrt > x)

        sqrt &= ~mulmask;

      mulmask >>= 1;

    }

  }

  return sqrt;

}*/

unsigned int current_read() {

  unsigned int _sum;

  unsigned long _sum_sq;

  cli();

  _sum = sum;

  _sum_sq = sum_sq;

  sei();

  /* calculate the variance using sum and sum_sq */

  return (N_SAMPLES*_sum_sq - _sum*_sum) / (N_SAMPLES*(N_SAMPLES-1));

}