ADC peripheral driver for ATmega328P

adc.c

/*
 * adc.c
 *
 * Analog-Digital Conversion example
 *
 * Hardware: 	ATMega328P at 16 MHz
 * Toolchain: 	avr-gcc v4.3.3
 * Editor:	Eclipse Kepler (4.0) with GNU Make
 * Usage:
 * 	Include and edit settings in adc.h and compile using 'make all'
 *
 *  Created on: 22-Jan-2014
 *      Author: Shrikant Giridhar
 */

#include "adc.h"


/* Debug Mode; Set on Release */
#define _DEBUG			1

#if _DEBUG

	#include <util/delay.h>
	#include <stdlib.h>
	#include "uart.h"

#endif

// Select channel of your choice
#define ADC_CHANNEL		CHANNEL_3

/*! Sets up ADC reference voltage, channel and output format */
void initADC(void)
{
	// Set selected channel as input
	DDRC &= ~_BV(ADC_CHANNEL);
	PORTC &= ~_BV(ADC_CHANNEL);

	// AVCC reference; right-adjusted; channel selection
	ADMUX |= (AVCC << REFS0) | (ADC_CHANNEL << MUX0);

	ADCSRA = (PRESCALAR_4 << ADPS0);
	ADC_ENABLE();


}

/*! \brief Retrieves converted data; blocking function */
uint16_t getConvData(void)
{
	/*
	 * There are a couple of ways of checking if the conversion is over.
	 * 1. In a single-ended conversion, the ADSC is cleared as soon as the
	 *    conversion is over otherwise it stays high.
	 * 2. The ADIF bit is set on conversion complete.
	 * 3. The ADIF bit could set off an interrupt to indicate end of conversion.
	 *
	 * Note that the first method wouldn't be useful if ADC is free-running, in
	 * which case methods 2 or 3 would be appropriate.
	 *
	 */

	uint16_t result;

	ADC_START();

	// while (ADCSRA & _BV(ADSC));
	while(!ADC_DONE());						// Stay here while conversion completes

	// ADC data update is blocked on reading ADCL, keeps read atomic
	// result = (uint16_t) (ADCL + (ADCH << 8));
	// Otherwise, just read the 16-bit register, ADCW
	result = (uint16_t) (ADCW);

	return result;
}

#if _DEBUG


	int main(void)
	{

		char adcData[10];
		uint16_t result;
		initADC();
		initUART();

		while(1)
		{

			result = getConvData();
			itoa(result, adcData, 10);
			writeString(adcData);
			putByte(' ');
			putByte('\r');
			putByte('\n');

		}
		return 0;

	}


#endif

adc.h

/*
 * adc.h
 *
 *  Created on: 23-Jan-2014
 *      Author: Shrikant Giridhar
 */

#ifndef ADC_H_
#define ADC_H_

#include <avr/io.h>
#include <stdint.h>

/* Auto-trigger options */
#define AUTO_TRIG	  	0

#if AUTO_TRIG

/* Define auto-triggering sources */

#define FREE_RUNNING	(0x00)
#define AN_COMPARATOR	(0x01)
#define EXT_IRQ			  (0x02)
#define TMR0_COMPA		(0x03)
#define	TMR0_OVF		  (0x04)
#define TMR1_COMPB		(0x05)
#define TMR1_OVF		  (0x06)
#define TMR1_CAP		  (0x07)

#endif

/* ADC Channel Selection */
#define CHANNEL_0		(PINC0)
#define CHANNEL_1		(PINC1)
#define CHANNEL_2		(PINC2)
#define CHANNEL_3		(PINC3)
#define CHANNEL_4		(PINC4)
#define CHANNEL_5		(PINC5)

/* Reference voltage settings */
#define	AREF			  (0x00)
#define AVCC			  (0x01)
#define BAND_REF		(0x03)

/* ADC Clock settings */
#define PRESCALAR_2		(0x01)		// ADC_CLK = CLK/2
#define PRESCALAR_4		(0x02)		// ADC_CLK = CLK/4
#define PRESCALAR_8		(0x03)		// ADC_CLK = CLK/8
#define PRESCALAR_16	(0x04)		// ADC_CLK = CLK/16
#define PRESCALAR_32	(0x05)		// ADC_CLK = CLK/32
#define PRESCALAR_64	(0x06)		// ADC_CLK = CLK/64
#define PRESCALAR_128	(0x07)		// ADC_CLK = CLK/128

/* Useful Macros */
#define POWER_DOWN()  (PRR |= _BV(PRADC))
#define ADC_ENABLE()  (ADCSRA |= _BV(ADEN))
#define ADC_DISABLE()	(ADCSRA &= ~_BV(ADEN))
#define ADC_START()	(ADCSRA |= _BV(ADSC))
#define ADC_DONE()	(ADCSRA & _BV(ADIF))
#define ADC_INTEN()	(ADCSRA |= _BV(ADIE))
#define AUTO_EN()		 (ADCSRA |= (AUTO_TRIG << ADATE))


/* Prototypes */
void initADC(void);
uint16_t getConvData(void);



#endif /* ADC_H_ */