How do you know what resources (timers and such) are being used in a sketch?

Question

I am a Arduino newbie (I am looking to develop a project for Arduino Day 2020), although a very familiar with AVR devices and C programming. I am struggling with trying to determine which resources, especially timers, are dedicated in support of various Arduino functions, like delay(), etc.? Is there any guide to resource restrictions? Are any of the EEPROM locations reserved?

Thanks in advance for any guidance on this subject.

Gene

beacon_dave · Accepted Answer

Just checked the Arduino Cookbook and it refers to: https://code.google.com/archive/p/arduino/wikis/HardwareResourceMap.wiki which may help.

fmilburn · Answer

Hi Gene, That is a good link that Dave gave. I haven't dug into Arduino in quite sometime but I once added a new board using Energia which is a fork of Arduino. Whenever a new board is added there are a couple of key files that must always be modified. For example, the pins for standard AVR boards on my Windows machine are located at ProgramFiles(x86).Arduino.hardware.arduino.avr.variants.standard.pins_arduino.h In that you will find code that identifies how things are mapped. For example, PWM and timers on a standard AVR: const uint8_t PROGMEM digital_pin_to_timer_PGM[] = {
 NOT_ON_TIMER, /* 0 - port D */
 NOT_ON_TIMER,
 NOT_ON_TIMER,
 // on the ATmega168, digital pin 3 has hardware pwm
#if defined(__AVR_ATmega8__)
 NOT_ON_TIMER,
#else
 TIMER2B,
#endif
 NOT_ON_TIMER,
 // on the ATmega168, digital pins 5 and 6 have hardware pwm
#if defined(__AVR_ATmega8__)
 NOT_ON_TIMER,
 NOT_ON_TIMER,
#else
 TIMER0B,
 TIMER0A,
#endif
 NOT_ON_TIMER,
 NOT_ON_TIMER, /* 8 - port B */
 TIMER1A,
 TIMER1B,
#if defined(__AVR_ATmega8__)
 TIMER2,
#else
 TIMER2A,
#endif
 NOT_ON_TIMER,
 NOT_ON_TIMER,
 NOT_ON_TIMER,
 NOT_ON_TIMER, /* 14 - port C */
 NOT_ON_TIMER,
 NOT_ON_TIMER,
 NOT_ON_TIMER,
 NOT_ON_TIMER,
};
#endif IIRC, the TI chips used the watchdog for the millis function. If you hunt around in this area you will find other variants and boards if they are loaded into the IDE with their pin allocation. The further you stray from the standard Arduinos the more you have to hunt to find out what is what as a lot of the boards aren't documented in a post like Dave's link. Most Arduino users aren't digging into it that deep though. I have never programmed the AVR boards with anything other than Arduino so can't comment on EEPROM (I am a TI MSP430 fanboy :-).

beacon_dave · Answer

On the Uno, I think Timer0 is used by delay(), millis(), and micros() functions, Timer1 by the Servo library and Timer2 by the tone() function.

How do you know what resources (timers and such) are being used in a sketch?

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