Has anyone tried software reset of an Arduino?

  • Contest Winner

    I'm doing some research on how to reset an Arduino from within a Sketch. My first choice would be to do this without connecting a wire to the reset pin.

    Here is an example. But I've read that it's not always the best way to perform a rest. I gues I have to try if the NFR accepts it 😉

  • Contest Winner

    I used it in a test sketch.

    void(* resetFunc) (void) = 0; //declare reset function @ address 0
    void loop() {
      if ( Serial.available() ) {
        // read the incoming byte:
        char incomingByte = Serial.read();
        // say what you got:
        Serial.print("I received: ");
        Serial.println(incomingByte, DEC );
        if ( incomingByte == 115 ) {
          Serial.println( "Resetting??" );
          gw.wait(50 ); // give serial some time to complete it's printing
          resetFunc();  //call reset

    And the Serial output is:

    send: 17-17-0-0 s=255,c=3,t=15,pt=2,l=2,sg=0,st=ok:0
    send: 17-17-0-0 s=255,c=0,t=17,pt=0,l=5,sg=0,st=ok:1.5.4
    send: 17-17-0-0 s=255,c=3,t=6,pt=1,l=1,sg=0,st=ok:0
    read: 0-0-17 s=255,c=3,t=6,pt=0,l=1,sg=0:M
    sensor started, id=17, parent=0, distance=1

    So on my Uno it seems to wok fine. Looks promissing

  • Mod

    @TheoL another way to reset is to enable the watchdog, but don't kick it. When it times out, it will reset the avr.
    Have to look up an example if you want.

  • Contest Winner

    @Yveaux Thank you for your quick reply. Don't ask why, but I need to be able to reset a node by sending a message to it ;-). It's desired functionality not because of hardware problems.

  • Mod

    @TheoL could very well be that 2.0.0 already supports it. Maybe @tekka can shed some light on it ?

  • Contest Winner

    @Yveaux That would be awesome. Saves me from code that might not be cross Arduino compatible. As I read somewhere during my research.

  • Admin

    @TheoL sending an C_INTERNAL/I_REBOOT will do the job, it's a wdt reset.

  • Contest Winner

    @tekka Thank you. Not yet sure how to do that. If you have an example for that I would be much obliged. Otherwise I'll spend some time on that later on. Either way, thanx again.

    Edited: Found it will update this answer later on with code

    Edit 2. My test didn't work, but I will try again tomorrow

  • Contest Winner

    Watchdog is used by sleep() function in mysensors, so it is not possible to use it. Also it is not safe to use it on arduino boards with standard bootloader. If I need watchdog on standard arduino boards (without mysensors library) with standard bootloader I use next ISR to handle WDT interrupt

    // Watchdog Timer interrupt service routine. This routine is required
    // to allow automatic WDIF and WDIE bit clearance in hardware.
    ISR (WDT_vect)
    	// WDIE & WDIF is cleared in hardware upon entering this ISR
    	asm volatile ("  jmp 0");

    This ISR prevents bootloop.
    If I need just soft reset arduino I use the technique very similar to TheoL's

    asm volatile ("  jmp 0"); //call anywhere

  • Contest Winner

    @Koresh I haven't seen assembler for a while. Do you use that on all of your projects?

  • Contest Winner

    In general - no. Only for such tricks 🙂 Of course these tricks are not invented by me.

  • Contest Winner

    @Koresh I understand my friend 😉 Although I have deep respect for people who are able to code completely in assembly. For me that was ages ago, almost in another life.

  • Admin

    @Koresh said:

    Watchdog is used by sleep() function in mysensors, so it is not possible to use it.

    Not sure what you are referring to, sleep() uses WDIE (wdt interrupt before reset, see here) whereas the reboot functionality is implemented via wdt reset (see here).

    Also it is not safe to use it on arduino boards with standard bootloader.

    Can you elaborate why?

  • Hardware Contributor

    @Koresh @TheoL i use wdt with mysensors..but i cheated a bit 🙂

    • you can use your own sleep and then handle wdt, but then careful if really need mysensors sleep(x ms) as it resets wdt.
    • or as i do too, i have added a weak empty function in mysensors lib to have isr wdt available from sketch ;), temporarily I will submit a pr for the few features i have added locally..

  • Contest Winner

    Standard bootloader can fail to switch off wdt after reboot (on the boards with most chips) and it will cause bootloop. After rebooting watchog is still working and it is very important to disable it. We can use modified bootloader or bootloader like optiboot.

  • Hardware Contributor

    @tekka I am not sure I will let answer, but if i remember well it was related to a problem that some old bootloader version were not handling properly wdt irq resulting in bootloader loop.

    ISR (WDT_vect) is used by mysensors lib if using mysensors sleep.

    but you can do something like:
    in MyHwATMega328.h

    void MY_WDT_Callback() __attribute__((weak));

    in MyHwATMega328.cpp, just add this in the wdt isr function

    if (MY_WDT_Callback) MY_WDT_Callback();

    and finally in your sketch you can use MY_WDT_Callback() which will be fired at every wdt irq. Something like

    void MY_WDT_Callback()   
      wdt_reset(); // or do what you want
      irqWdt = true;

    maybe there are better ways. another note, is I don't advice to do too much change locally without pr because then..arrghh 😔 😱

  • Contest Winner

    I when you thought you finally knew a bit about the Arduino, there comes a topic like this 😉 Thanx to you all. I understand to I have still much to learn.

  • Hi, as I remember about watchdog is to set it to 8S, so there is enough time to upload an sketch (8 seconds) before the Arduino will reboot. WDT0_time_in_seconds. If using WDT08S Always call the wdt_reset() no later than 7 seconds to avoid reset/reboot. This is usually used in case that the Arduino/avr is "hanging" in an infinite loop and stopped responding to actions, then this will automatically reset/reboot

    Include this in your sketch:
    #include <avr/wdt.h>

    setup ();{
    // WDTO_1S
    // WDTO_2S
    // WDTO_4S
    // WDTO_8S

    loop (){
    wdt_reset(); // You must call this within less seconds set as WDT0_8S

  • For whatever strange reason, the Arduino stock bootloader is broken, so that it will not disable the watchdog on startup, causing just an infinite reset loop. I'd recommend updating the bootloader with something like MYSBootloader or Optiboot.

  • Banned

    Hey Buddy,

    [spam post removed by moderator]

  • @donnacarter0103

    The third way to reset an Arduino is to use watchdog (Need to flash another bootloader as the default have disabled watchdog), enable watchdog, and remember to reset it often in your code, else it will reste the Arduino

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