Pages: [1]   Go Down
Author Topic: Arduino source code. What does the function analogRead() in C ?  (Read 375 times)
0 Members and 1 Guest are viewing this topic.
France
Offline Offline
Jr. Member
**
Karma: 1
Posts: 85
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi guyes.

I'm struggling with some stuff at the moment and the only explanation or example I find are written in C.
As you know Arduino is not  genuine C and I'd like to know where I can find information for instance how Arduino functions are written.

Let say, what an analogRead() do ?
It has to do with some ADMUX and ADCSRA stuff I guess.

Now I've been playing Arduino for a while, I think I need to go deeper and make the link between Arduino and real C language working with port and so on.

Hope I'm going the right direction.

Logged

UK
Offline Offline
Tesla Member
***
Karma: 141
Posts: 7994
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Arduinos use genuine C/C++. The Arduino IDE just hides some of the housekeeping nonsense.

All the details of the Atmega328 are explained in the Atmel datasheet.

The full Arduino source code is included with the IDE.

...R
Logged

France
Offline Offline
Jr. Member
**
Karma: 1
Posts: 85
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Arduinos use genuine C/C++. The Arduino IDE just hides some of the housekeeping nonsense.


What do you mean by "housekeeping nonsense" ?


The full Arduino source code is included with the IDE.

Sorry but I've no idea how to reach it !
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 362
Posts: 17307
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset


on my machine the file wiring_analog.c is located at:

C:\Users\Lawrence\Documents\Arduino\hardware\arduino\cores\arduino

Code:
/*
  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(__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
#elif defined(analogPinToChannel) && (defined(__AVR_ATtiny25__) || defined(__AVR_ATtiny45__) || defined(__AVR_ATtiny85__))
pin = analogPinToChannel(pin);
#else
if (pin >= 14) pin -= 14; // allow for channel or pin numbers
#endif

#if defined(__AVR_ATmega32U4__)
pin = analogPinToChannel(pin);
ADCSRB = (ADCSRB & ~(1 << MUX5)) | (((pin >> 3) & 0x01) << MUX5);
#elif 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(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);
}
}
}
}


Logged

North Queensland, Australia
Offline Offline
Edison Member
*
Karma: 76
Posts: 2247
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

The source code is available online too.

https://github.com/arduino/Arduino/blob/ide-1.5.x/hardware/arduino/avr/cores/arduino/wiring_analog.c
Logged


UK
Offline Offline
Tesla Member
***
Karma: 141
Posts: 7994
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The "housekeeping nonsense" is all the junk you need in a "regular" C/C++ program such as a function called main(), the need to declare function prototypes, lots of #includes, .h files etc etc etc etc.

No doubt it was all designed to ensure that the faint-hearted drop out so there is a limited supply of C programmers on the market in order to keep salaries up. smiley

...R
Logged

France
Offline Offline
Jr. Member
**
Karma: 1
Posts: 85
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Well.

Maybe my question wasn't correct.
What lead me to this question is that topic I've started :
http://forum.arduino.cc/index.php?topic=236066.0

I thought I was facing some C instead of Arduino code, but as I'm beginner, I might have been wrong !

Logged

UK
Offline Offline
Tesla Member
***
Karma: 141
Posts: 7994
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Don't double post. It's impossible to have a conversation in two different threads.

Arduino code is C/C++. There is nothing else.

I am not going to comment on the other Thread here.

...R
Logged

Pages: [1]   Go Up
Jump to: