#include <avr/io.h>


void adc_init(void) {
	uint16_t dummyResult;
	// AVCC with external capacitor at AREF pin
	ADMUX = _BV(REFS0);  
 
	// set frequency prescaler to 64
	ADCSRA = _BV(ADPS2) | _BV(ADPS1);
	
	// enable ADC	
	ADCSRA |= _BV(ADEN);
 
	// make a dummy read out
	ADCSRA |= _BV(ADSC);
	while (ADCSRA & _BV(ADSC) ) {
	}
	
	// we have to read, otherwise the next result is not available
	dummyResult = ADCW;
}


uint16_t adc_read_single(const uint8_t channel) {
    // strip all MUX bits, keep the 3 msb (REFS1, REFS0, ADLAR)
    ADMUX = (ADMUX & ~(0x1F)) | (channel & 0x1F);
    ADCSRA |= _BV(ADSC);
    while (ADCSRA & _BV(ADSC) ) {
    }
    return ADCW;
}
 
uint16_t adc_read_avg(const uint8_t channel, const uint8_t nsamples) {
    uint16_t sum = 0;
    uint8_t count = nsamples % 60;

    for (uint8_t i=0; i<count;++i ) {
        sum += adc_read_single(channel);
    }

    return (sum / count);
}