Introduction: Two Ways to Reset Arduino in Software

If you want to RESET Arduino from the beginning without manually pressing the RESET button, there are a few ways. Here are two ways, using minimal wiring / circuitry. 

Step 1: Using 1 Wire Connected to the RESET Pin

1. electronically, using only 1 wire connecting an OUTPUT pin (12 in this example) to the RESET pin. (see the circuit)

In this example, pin 13, connected to the internal LED pin 13 is blinking. Pin 12 gets connected to the RESET pin by one wire.
-Typically, this would be a problem because when the application starts up, all pins get pulled LOW. This would therefore disable Arduino from every running. BUT, the trick is: in setup() function, the FIRST thing that happens is we write HIGH to the pin 12, which is called our reset pin (digitalWrite(resetPin, HIGH), thereby pulling the Arduino RESET pin HIGH. 

Step 2: Using Just Software

In this example, you do not need any extra wiring. We initialize the reset function, then call reset.

void(* resetFunc) (void) = 0;//declare reset function at address 0
...
resetFunc(); //call reset 

Comments

author
illumation_ (author)2017-09-01

The second method crash the Arduino, the Leonardo (Pro Mini) at least. So I think that is an hack and not a real solution. Normally, a null pointer (aka adress 0) is an unusable invalid address, when call or use a null pointer to access things, strange things can happen. In fact a bad instruction that can cause a crash or a reboot. Don't use it, it is not reliable.

author
stevenk37 (author)2016-01-04

Well.. #1 is not really a software solution, is it, if you have to wire pins.. Also, this is not an advised solution, according to what I've read before.

#2 Is just a hack that anyone could come up with, but still doesn't provide a real watchdog functionality (you have to trigger it, and thus can only be used as a reset method, not a WD (which seems to be what sme of you guys need).

Let me give some details on the built-in arduino WD (yes, really) that can be used both as WD or as a reset device.

You can set it from 15ms to 8s range. You need to reset it in software or otherwise it will trigger a reset (reverse to #2 method).

Here's how to use it;

#include <avr/wdt.h> //should be in any adruino IDE

void setup() {
wdt_disable(); //always good to disable it, if it was left 'on' or you need init time
//do some stuff here
wdt_enable(WDTO_8S); //enable it, and set it to 8s
}

void loop() {
//do some stuff here
wdt_delay(5000) //instead of delay, i made my own delay to reset the WDT
}

//this makes sure the WDT is reset immediately when entering the
//function, but we can still benefit from a real 'delay'.
//upon leaving the function, we reset it again.
//i realize timing will be loose, you can always do something with
//millies() if you need strict timing.
//you might also need to adjust the '1000' if you WDT is shorter

void wdt_delay(unsigned long msec) {
wdt_reset();

while(msec > 1000) {
wdt_reset();
delay(1000);
msec -= 1000;
}
delay(msec);
wdt_reset();
}

//to reload the board, you only have to delay > WDT
//another option is to set the WDT very short, and do a short delay

void wdt_reload() {
delay(8001);
}

author
gussmith (author)stevenk372017-08-12

This is interesting. Is the reset by the watchdog timer the same as if you would press the reset button?

author
stevenk37 (author)gussmith2017-08-18

this has been discussed on the arduino playground. see https://playground.arduino.cc/Main/ArduinoReset

author
FirstN1 (author)stevenk372016-09-26

I am sorry to say this, but many times the comments are much more useful than the article itself. Thank you.

author
pinp2 (author)stevenk372016-05-02

Thank you stevenk37 for an Arduino Watchdog. It is does the trick I need.

It would be good if you would create a separate entry about it cause not all people read through comments :)

author
TimN33 (author)2016-06-22

Isn't a software reset a bit scary?

Maybe you can answer this: if the loop simply called the reset function every time. then you could never stop it, or am I mistaken? Is there something in the arduino PC app that allows you to break into it?

author
MithunK3 (author)TimN332017-08-03

Yup its every bit scary. If you mistakenly put in some bad logic and burn it on the board and reset gets called in every loop your board will not remain programmable anymore!

author
akn10red (author)TimN332016-08-16

Well it depends on your software logic. Lets say you are controlling your arduino from smartphone via wifi/bluetooth. You send a command from your phone to change (lets say) the wifi ssid or password it is connecting to.... You get that command in arduino, store the new ssid/password in eeprom or sd card and RESET your arduino. Now when your arduino resets it will get the data from eeprom/sd card and connect with new wifi credentials.

author
BerryM4 (author)2017-07-11

Hi, my name is marlin. Good article, this is very interesting and can increase my knowledge. thank you for sharing. always success

<a href="http://arduinounotutorials.com/">Arduino Tutorial For Begginers</a><br />

<a href="http://arduinounotutorials.com/simple-arduino-uno-projects-with-code-for-beginners/">Arduino Uno Project For Beginners</a><br />

<a href="http://arduinounotutorials.com/reprogramming-erasing-and-resetting-arduino-uno-tutorial/">How To Reset Arduino Uno</a>

author
micahmelnyk (author)2017-06-30

Thanks Gabby for posting this.

One comment perhaps of interest to some, I have found more success with the hard reset (using a pin to take the reset LOW) than the soft reset in terms of serial communications stability. With the soft reset I would often get garbled serial communications after reset, while with the hard reset (still resetting based on the software, but requiring additional external wiring) the serial comms were stable every time.

author
katonafull (author)2016-10-20

I found the solution to save String (or anithing else) from a subrutine that you have to reset.
You have to store the data in the Flash or the EEPROM memori.
I especially store my String class in the EEPROM. You can follow that here: http://forum.arduino.cc/index.php?topic=333521.new#new

author
LoryanT (author)2016-10-07

what if like this is happened what maybe the next step

author
AnthonyP15 (author)2016-04-27

Very helpful, thankyou.

author
werose (author)2016-02-18

thank you for that

author
BadASszZ (author)2016-02-06

Thanks, just what I was looking for. :)

author
ali alshamary (author)2015-12-20

Wonderful, I have benefited from it, Thanks

author
wilber adonayP (author)2015-12-04

Hi all, I need help, the Arduino Uno can be used only once or is there some way to put factory again, I would appreciate the help because I'm new at this. THANKS

author
stringstretcher (author)2012-11-09

Ok, so teach me, why would I need to do this / want to do this? Why wouldn't this just loop, resetting over and over?

author

This post is EXACTLY what I needed! The software reset (Step 2 in this instructable) works perfectly for what I need to do. I am using an nRF24L01+ 2.4GHz transceiver, with the RF24 library by ManiacBug, and I used the above software reset code to make my program more robust. In certain circumstances (for example, a brown-out on the 3.3V power pin to the RF24L01+ module), the transceivers lose connection and stop working. I tried for many hours to get the 2.4GHz modules to reset themselves and reconnect, but I could not figure it out. Finally, I wrote a code that says to each device, "if you haven't received a successful packet in 100ms" (average time to do so is 5ms for my code), "then do an Arduino software reset." This works! Finally, I can get the modules to automatically reconnect if they have an anomaly that causes them to lose connection. So...to answer your question, this is where the software reset code is useful!

~Gabriel

electricrcaircraftguy.blogspot.com

author
hakk3r (author)panther30012015-09-21

BTW. This is exactly the same issue I've experienced and the reason I use this code. Very useful.

author
panther3001 (author)panther30012014-01-30

PS. more info. on the module is here: http://arduino-info.wikispaces.com/Nrf24L01-2.4GHz-HowTo

author
Nadr0j (author)stringstretcher2012-12-19

You're right. In this example it will loop indefinitely.

It could have more useful applications in larger programs though. For example..

I once wrote a program when I was in geometry for a watch to extend its functionality. After every set of numbers I input I wanted it to give me an answer, wait 5 seconds and then reset itself so it was primed up for another set of numbers.

Admittedly this was a very lazy way for me do accomplish this but it got the job done.

Hope that helps.

author
hakk3r (author)2015-09-21

Great article thanks! Step 1 works like a charm. Only problem is that once I set the reset pin to OUTPUT I lose connection to the programmer and the next time i go to upload avrdude complains that it can't access the board (like RX is blocked). So if you run into this, make sure you only enable the pin right before you release the board to use. Otherwise the only way I found I can reprogram the board is to disconnect/reconnect the board and quickly push out the newer version before that pin goes to OUTPUT.

author
burn317 (author)2015-07-09

So happy I found this thread! I'm building a starter project of an autonomous wheeled bot with ultrasonics that fairly frequently report a ping of 0 when I start it up for the first few tries.
I decided to put a simple systems check into the setup so it will check the motors and ultrasonics are functioning both on the software side (ultrasonics), and the hardware side (enough juice in the batteries to run?).
The second method listed here finally solved my if statement problem I was having!

author
PramodT (author)2015-05-22

Does the watchdog reset affect the external RESET pin? I mean WDT resets the device, does the RESET pin go LOW(assuming RESET pin to be active LOW and is tied high always)?

author
nqtronix (author)PramodT2015-05-26

No, both reset circuits are completly sepereate.

Check the datasheet, chapter 11 Figure 11-1 for the "Reset Logic". Arrows indicate a on-way signal, similar to a simple diode.

Hope this helps :)

author
praju1 (author)2015-05-06

This is really helpful. Tried using software reset and it worked for my project.

author
costy35 (author)2015-02-01

I used

asm volatile("rjmp 3584\n\t");

Where 3584=$0E00 (bootloader address)

But is little difficult ,because bootloader address can may differ from one arduino to other!

It's equivalent with hardware reset (reset button)

reset function to address 0, is not ecquivalent with hardware reset.

author
soapergem (author)costy352015-02-04

Thanks costy35. How would one go about finding out what the $0E00 bootloader address is for any given board?

author
costy35 (author)soapergem2015-02-11

Any board (atmega processor) have custom bootloader address. You can see and decode fusebit of ....

your_arduino_folder_program\hardware\arduino\boards.txt

and see fusebits... but here not talk about this problem ... it's only an idea!!!

author
subnet (author)2014-11-09

thanks, very helpful :-)

the method 2 seems to work for me even out of a for loop, if using it in a if statement, but only if resetFunc function is declared before setup.

author
NomanAhmed3 (author)2014-08-18

it really helped thanks

author
laptophead (author)2014-03-03

I tried to apply your sketch to reset the processor as soon as a number count was larger than 33. It did not work, I wonder if you can help.

Thanks a lot

Mitch

void(* resetFunc) (void) = 0;//declare reset function at address 0

void loop()
{




for (int i=0; i <= 255; i+=3){
Serial.println(i);
delay(1);
}
resetFunc();

if (i>33) {
resetFunc();
}


}

author
manuradha (author)laptophead2014-05-16

you have to call the resetFunc() in side the "for" loop like.

void(* resetFunc) (void) = 0;//declare reset function at address 0


void loop()

{


for (int i=0; i <= 255; i+=3){
Serial.println(i);

if (i>33) {
resetFunc();
}

delay(1);
}


}

author
ma_partha (author)manuradha2014-06-11

Why should resetFunc() be called inside a loop? Why does it not work if it is called outside the "for" loop?

author
manuradha (author)ma_partha2014-06-12

in the cord above ........ int "i" variable is declared inside the FOR loop, and infarct the variable that drives the FOR loop(till "i" reach 255)... And it is a local variable so it can not be accessed outside the loop... also in this case if some how we could access the "I", by the time FOR loop finish it would be 255 :)

author
Hwolfw (author)laptophead2014-03-11

The for loop doesn't include what you want it to do. The way you coded it, it will continue up to 255 then reset, never reaching the if statement.

void(* resetFunc) (void) = 0;//declare reset function at address 0
void loop()
{
for (int i=0; i <= 255; i+=3){
if (i>33) { //needs to be within the loop
resetFunc(); //to check i for greater than 33
}
Serial.println(i);
delay(1);
}
resetFunc();

//outside of loop, will never be looked at.
// if (i>33) {
// resetFunc();
// }
}

author
linker210 (author)2013-12-14

Is there a way reset millis to a previous time besides zero using this function?

author
retrolefty (author)2013-03-10

If you look in any Atmel AVR datasheet they will explicitly tell you that this in not an acceptable method to reset a chip. Upon reset all I/O pins are set to input mode so you lose the LOW output from pin 12 in this example. This doesn't allow the reset low pulse to met the minimum low pulse width it has to be for a valid reset process. So use at your own risk. There is a valid way to reset a AVR chip in software without even needing a wired added as here. Just enable the watch dog timer and let it time out which will generate a true reset. Then in the setup function disable the WDT.
Lefty.

author
BooRan (author)2012-11-09

I've used this technique before just to see if it worked and it seemed useful. One comment though is that i would recommend using a resistor in there. Sending a high signal straight to the Reset pin could cause a short circuit and fry your chip. Not sure what would work better though, a pull up resistor from the reset pin to high, and allowing the "resetPin" to pull it low, or just placing a resistor between the two points.

author
pdemetrios (author)2012-11-08

There are and the WDT method for all the micros with WDT .
Setup the WDT and then make an infinity loop

WDTCSR=(1< WDTCSR= (1< for(;;)
and in the 16ms the mcros will reset and the MCUSR variable will
have the value WDRF
With your software the MCUSR will have an Unspecified value.

author
pdemetrios (author)pdemetrios2012-11-08

sorry but the code has modified the correct is
WDTCSR=(1<<WDE) | (1<<WDCE) ;

    WDTCSR= (1<<WDE)

for(;;)

author
amandaghassaei (author)2012-11-08

nice, never thought about this, thanks for posting!

author
billhorvath (author)2012-11-07

Neato! Thanks for the tips!

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