root / toolbox / current.c @ f15d9227
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#include "current.h" |
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#include <avr/io.h> |
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#include <avr/interrupt.h> |
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#include <math.h> |
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#define CYCLES_PER_SECOND 60 // wall power |
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#define SAMPLES_PER_CYCLE 16 |
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#define N_SAMPLES 48 |
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unsigned int samples[N_SAMPLES]; |
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int sample_idx;
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unsigned int sum; |
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unsigned long sum_sq; |
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void current_init() {
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/* TODO reduce power consumption with DIDR* */
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/*
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* COM1A = COM1B = 0, disconnect pins
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* WGM1 = 4, clear timer on compare A
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* CS1 = 1, no prescaler
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*/
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TCCR1B = _BV(WGM12) | _BV(CS10); |
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/* Timer is cleared on A, ADC is triggered on B */
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OCR1A = F_CPU / SAMPLES_PER_CYCLE / CYCLES_PER_SECOND; |
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OCR1B = OCR1A; |
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/*
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* REFS = 0, Vcc reference (set to 2 for internal 1.1V reference)
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* MUX = 8, PB3(ADC8)
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*/
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ADMUX = _BV(MUX3); |
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/*
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* ADLAR = 0, right adjust result
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* ADTS = 5, start on timer 1 compare match B
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*/
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ADCSRB = _BV(ADTS2) | _BV(ADTS0); |
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/*
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* ADEN = 1, enable
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* ADSC = 0, don't start yet
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* ADATE = 1, auto trigger
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* ADIE = 1, enable interrupt
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* ADPS = 6, prescale clock by 64
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*/
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ADCSRA = _BV(ADEN) | _BV(ADATE) | _BV(ADIE) | _BV(ADPS2) | _BV(ADPS1); |
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} |
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ISR(ADC_vect) { |
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unsigned int old, new; |
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/* clear the timer interrupt flag so that the ADC will be triggered again
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* next time the timer resets */
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TIFR |= _BV(OCF1B); |
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new = ADC; |
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/* put sample into ring buffer */
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old = samples[sample_idx]; |
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samples[sample_idx++] = new; |
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if (sample_idx == N_SAMPLES)
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sample_idx = 0;
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/* keep a running total of samples and samples squared */
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sum += new; |
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sum -= old; |
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sum_sq += (unsigned long)new*new; |
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sum_sq -= (unsigned long)old*old; |
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} |
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unsigned int current_read() { |
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unsigned int _sum; |
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unsigned long _sum_sq; |
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cli(); |
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_sum = sum; |
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_sum_sq = sum_sq; |
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sei(); |
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/* calculate the variance using sum and sum_sq */
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return (N_SAMPLES*_sum_sq - (unsigned long)_sum*_sum) / |
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(N_SAMPLES*(N_SAMPLES-1));
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} |