adc.c

// This is NOT GPL or any other ""free"" software license. 
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//
//
// (C) 2015 Mike Brent aka Tursi aka HarmlessLion.com
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#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <string.h>
#include "main.h"
#include "adc.h"

void AdcInit() {
	// configure ADC
	ADMUX 	= 0x20;		// left justify, MUX0, AREF. Note that this bit must always be set for correct results in this application!
	ADCSRA 	= 0x84;		// ADC on, prescaler of CLK/16 - this results in a worst-case conversion time of about 26uS, but we read twice (for MUX settling time) to make 52uS
	ADCSRB	= 0x00;		// no auto-trigger
	DIDR0	= 0x0f;		// disable digital inputs on pins 0-3
}

int AdcRead(unsigned char page, unsigned int address) {
	if (page > 3) {
		// only four ADCs
		return -1;
	}
	if (address < 0x20) {
		return 0;
	}

	ADMUX = 0x20 | page;			// select the correct ADC channel

	// do it once, dummy read
	ADCSRA = 0xC6;					// default settings as above, plus START bit (0x40)
	// wait for the conversion to finish
	while (ADCSRA & 0x40) { }

	// do it again, this time for real
	ADCSRA = 0xC6;					// default settings as above, plus START bit (0x40)
	// wait for the conversion to finish
	while (ADCSRA & 0x40) { }

	// return the result (only need the top 8 bits, though 12 bits are available)
	return ADCH;
}

HANDLERS AdcHandlers = {
	AdcInit, AdcRead, DummyWrite
};