Is it possible to reset the Arduino with a software command?

Question

I am now resetting using "asm volatile (" jmp 0"); and it works but I would like to leave the variables as is. I want to leave the LCD backlight off. I can supply the code if necessary. Thanks, Bill

shabaz · Accepted Answer

Hi Bill, A software reset can (sometimes) be a good thing to do to handle situations as you describe (program runaway for instance). I was just addressing that second point in you original question, i.e, regardless of the way the reset occurs (jmp zero, watchdog programmed reset, or forcing a pin as mcb1 mentions), the variables can not be assumed to remain the same (despite power not having been removed from the chip), because in-between the reset and the Arduino main/loop etc, there is a bit of invisible code (called C startup or similar) which will force some variable storage to zero. Any that are not forced to zero cannot be presumed to be uncorrupted anyway, due to the program runaway which might have caused the reset (so that was the only reason I wanted to confirm why the reset was to occur, because we have to presume loss of all state information upon reset (regardless of the way the reset occurs) unless state can be inferred from elsewhere (e.g. logic levels on pins or non-volatile memory).

Robert Peter Oakes · Answer

essentially it would be as if you hit the reset button. Remember the Arduino code is at a very high level, abstracting much of the hardware and even code from the developer, the typical developer using "Wiring" to code the arduino is not even close to the machine. The watchDog Timer will trigger a reset by entering into a defined address and executing the code found there, this is all explained in the linked article I provided. It is not quite the same as powering off then on, but it is as close to hitting the reset button as you can get.

shabaz · Answer

Hi Bill,

That may be tricky, depending on the scope some variables are set to zero automatically, and others will have different content (i.e. non-zero).

However, one option is to write your data to EEPROM, which of course is persistent even after power loss.

Is there a reason you wish to reset? Ordinarily you'd never do that (unless a software failure was detected, e.g. using a watchdog timer)

or some rare scenario like a software upgrade. (normal practice is to never allow have the microcontroller to reset or exit).

clem57 · Answer

Why not set the LCD backlight off and go into a do while loop forever?

mcb1 · Answer

Not that I am a software programmer, but I tend to force/set variables either during the initial declaration or during void setup(). Call me stupid but I always imagined it was better to be sure. Mark

Robert Peter Oakes · Answer

I think more specifically it would be fare to say you "Can Not Guarantee" the preservation of volatile RAM through a reset condition so therefor should NEVER rely on it happening If you need variables preserving across resets either software invoked or Power Cycle then you need to use None Volatile RAM, either the EEPROM or an external SD Card

Is it possible to reset the Arduino with a software command?

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