voltage reference and resolution; is there some register or function that return

Hi.

I'm want to know if there any variable, register or function already integrated in arduino that can return the bit resolution for analogRead() and voltage reference(3.3,5 or 1,1 volt?

it is to simplify the use of analog input library to do not have to explicitly pass them each time as argument. like:

class Pressure {
public:
    Pressure(float vRef, uint8_t reso);
    float pressure(uint8_t input);

private:
    uint16_t _reso = 1023;
    float _vRef = 5;
    float Vin(uint8_t input);
    uint16_t average(uint8_t input);
};

I is to simplify the migration to Uno or DUE. I wonder if the constructor can get the value of ioRef and the bitrade reso without argument.

The resolution is 1024 not 1023 (this is only the highest value),
as this is platform depending you can probably use an #ifdef.

The currently selected analog reference is available via

extern uint8_t analog_reference;

Have a look at wiring_analog.c

/*
  wiring_analog.c - analog input and output
  Part of Arduino - http://www.arduino.cc/

  Copyright (c) 2005-2006 David A. Mellis

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General
  Public License along with this library; if not, write to the
  Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  Boston, MA  02111-1307  USA

  Modified 28 September 2010 by Mark Sproul

  $Id: wiring.c 248 2007-02-03 15:36:30Z mellis $
*/

#include "wiring_private.h"
#include "pins_arduino.h"

uint8_t analog_reference = DEFAULT;

void analogReference(uint8_t mode)
{
	// can't actually set the register here because the default setting
	// will connect AVCC and the AREF pin, which would cause a short if
	// there's something connected to AREF.
	analog_reference = mode;
}

int analogRead(uint8_t pin)
{
	uint8_t low, high;

#if defined(analogPinToChannel)
#if defined(__AVR_ATmega32U4__)
	if (pin >= 18) pin -= 18; // allow for channel or pin numbers
#endif
	pin = analogPinToChannel(pin);
#elif defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
	if (pin >= 54) pin -= 54; // allow for channel or pin numbers
#elif defined(__AVR_ATmega32U4__)
	if (pin >= 18) pin -= 18; // allow for channel or pin numbers
#elif defined(__AVR_ATmega1284__) || defined(__AVR_ATmega1284P__) || defined(__AVR_ATmega644__) || defined(__AVR_ATmega644A__) || defined(__AVR_ATmega644P__) || defined(__AVR_ATmega644PA__)
	if (pin >= 24) pin -= 24; // allow for channel or pin numbers
#else
	if (pin >= 14) pin -= 14; // allow for channel or pin numbers
#endif

#if defined(ADCSRB) && defined(MUX5)
	// the MUX5 bit of ADCSRB selects whether we're reading from channels
	// 0 to 7 (MUX5 low) or 8 to 15 (MUX5 high).
	ADCSRB = (ADCSRB & ~(1 << MUX5)) | (((pin >> 3) & 0x01) << MUX5);
#endif
  
	// set the analog reference (high two bits of ADMUX) and select the
	// channel (low 4 bits).  this also sets ADLAR (left-adjust result)
	// to 0 (the default).
#if defined(ADMUX)
	ADMUX = (analog_reference << 6) | (pin & 0x07);
#endif

	// without a delay, we seem to read from the wrong channel
	//delay(1);

#if defined(ADCSRA) && defined(ADCL)
	// start the conversion
	sbi(ADCSRA, ADSC);

	// ADSC is cleared when the conversion finishes
	while (bit_is_set(ADCSRA, ADSC));

	// we have to read ADCL first; doing so locks both ADCL
	// and ADCH until ADCH is read.  reading ADCL second would
	// cause the results of each conversion to be discarded,
	// as ADCL and ADCH would be locked when it completed.
	low  = ADCL;
	high = ADCH;
#else
	// we dont have an ADC, return 0
	low  = 0;
	high = 0;
#endif

	// combine the two bytes
	return (high << 8) | low;
}

// Right now, PWM output only works on the pins with
// hardware support.  These are defined in the appropriate
// pins_*.c file.  For the rest of the pins, we default
// to digital output.
void analogWrite(uint8_t pin, int val)
{
	// We need to make sure the PWM output is enabled for those pins
	// that support it, as we turn it off when digitally reading or
	// writing with them.  Also, make sure the pin is in output mode
	// for consistenty with Wiring, which doesn't require a pinMode
	// call for the analog output pins.
	pinMode(pin, OUTPUT);
	if (val == 0)
	{
		digitalWrite(pin, LOW);
	}
	else if (val == 255)
	{
		digitalWrite(pin, HIGH);
	}
	else
	{
		switch(digitalPinToTimer(pin))
		{
			// XXX fix needed for atmega8
			#if defined(TCCR0) && defined(COM00) && !defined(__AVR_ATmega8__)
			case TIMER0A:
				// connect pwm to pin on timer 0
				sbi(TCCR0, COM00);
				OCR0 = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR0A) && defined(COM0A1)
			case TIMER0A:
				// connect pwm to pin on timer 0, channel A
				sbi(TCCR0A, COM0A1);
				OCR0A = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR0A) && defined(COM0B1)
			case TIMER0B:
				// connect pwm to pin on timer 0, channel B
				sbi(TCCR0A, COM0B1);
				OCR0B = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR1A) && defined(COM1A1)
			case TIMER1A:
				// connect pwm to pin on timer 1, channel A
				sbi(TCCR1A, COM1A1);
				OCR1A = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR1A) && defined(COM1B1)
			case TIMER1B:
				// connect pwm to pin on timer 1, channel B
				sbi(TCCR1A, COM1B1);
				OCR1B = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR1A) && defined(COM1C1)
			case TIMER1C:
				// connect pwm to pin on timer 1, channel B
				sbi(TCCR1A, COM1C1);
				OCR1C = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR2) && defined(COM21)
			case TIMER2:
				// connect pwm to pin on timer 2
				sbi(TCCR2, COM21);
				OCR2 = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR2A) && defined(COM2A1)
			case TIMER2A:
				// connect pwm to pin on timer 2, channel A
				sbi(TCCR2A, COM2A1);
				OCR2A = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR2A) && defined(COM2B1)
			case TIMER2B:
				// connect pwm to pin on timer 2, channel B
				sbi(TCCR2A, COM2B1);
				OCR2B = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR3A) && defined(COM3A1)
			case TIMER3A:
				// connect pwm to pin on timer 3, channel A
				sbi(TCCR3A, COM3A1);
				OCR3A = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR3A) && defined(COM3B1)
			case TIMER3B:
				// connect pwm to pin on timer 3, channel B
				sbi(TCCR3A, COM3B1);
				OCR3B = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR3A) && defined(COM3C1)
			case TIMER3C:
				// connect pwm to pin on timer 3, channel C
				sbi(TCCR3A, COM3C1);
				OCR3C = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR4A)
			case TIMER4A:
				//connect pwm to pin on timer 4, channel A
				sbi(TCCR4A, COM4A1);
				#if defined(COM4A0)		// only used on 32U4
				cbi(TCCR4A, COM4A0);
				#endif
				OCR4A = val;	// set pwm duty
				break;
			#endif
			
			#if defined(TCCR4A) && defined(COM4B1)
			case TIMER4B:
				// connect pwm to pin on timer 4, channel B
				sbi(TCCR4A, COM4B1);
				OCR4B = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR4A) && defined(COM4C1)
			case TIMER4C:
				// connect pwm to pin on timer 4, channel C
				sbi(TCCR4A, COM4C1);
				OCR4C = val; // set pwm duty
				break;
			#endif
				
			#if defined(TCCR4C) && defined(COM4D1)
			case TIMER4D:				
				// connect pwm to pin on timer 4, channel D
				sbi(TCCR4C, COM4D1);
				#if defined(COM4D0)		// only used on 32U4
				cbi(TCCR4C, COM4D0);
				#endif
				OCR4D = val;	// set pwm duty
				break;
			#endif

							
			#if defined(TCCR5A) && defined(COM5A1)
			case TIMER5A:
				// connect pwm to pin on timer 5, channel A
				sbi(TCCR5A, COM5A1);
				OCR5A = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR5A) && defined(COM5B1)
			case TIMER5B:
				// connect pwm to pin on timer 5, channel B
				sbi(TCCR5A, COM5B1);
				OCR5B = val; // set pwm duty
				break;
			#endif

			#if defined(TCCR5A) && defined(COM5C1)
			case TIMER5C:
				// connect pwm to pin on timer 5, channel C
				sbi(TCCR5A, COM5C1);
				OCR5C = val; // set pwm duty
				break;
			#endif

			case NOT_ON_TIMER:
			default:
				if (val < 128) {
					digitalWrite(pin, LOW);
				} else {
					digitalWrite(pin, HIGH);
				}
		}
	}
}