Watchdog on Arduino Nano does not recover

Question

I'm trying to add a watchdog on an Arduino Nano, for my code, and I'm following the code in this manual exactly, but after the amount of time for not resetting the watchdog, it resets but does not reboot.

In the last paragraph it says that:

However, I could not find something similar in Optiboot bootloader (If I'm wrong, correct me please!), used by Arduino UNO and other new boards. It seems that they sacrificed this check for size. So, it is possible that watchdog timer will be enabled after reset, so - if you set it's value too low, your board may never come out of bootloader stage. So, to be always on the safe side, set watchdog to longer periods (2S and more).

So I've tried for 8 s, but still same result.

What is wrong?

#include <avr/wdt.h>
int k=1;

void setup() {
  Serial.begin(9600);
  wdt_enable(WDTO_8S);
}

void loop() {
  //do stuff here
  k++;
  wdt_reset();
  Serial.println(1000 * k);
  delay(1000 * k);
}

Answer 1

the "old" Nano bootloader doesn't clear the Watchdog flag and while the bootloader waits for the upload, the board resets.

flash the "new" bootloader to Nano

In IDE 1.8.6 you can select version of Nano in Tools menu. It is the 'new' bootloader if you select "Atmega328p" and 'old' if you select "Atmega328p (Old bootloader)". If you invoke "Burn bootloader" it will use the bootloader for the selected option.

Answer 2

This works on an Uno R3.

The sketch restarts every 4 seconds when wdt_reset() is commented out.

Please copy the code and try it.

  #include <avr/wdt.h>

  void setup() {
    pinMode(13,OUTPUT);
    digitalWrite(13,LOW);

    delay(50);
    digitalWrite(13,HIGH);    // flicker the LED to identify when setup() is running
    delay(50);
    digitalWrite(13,LOW);
    delay(50);
    digitalWrite(13,HIGH);
    delay(50);
    digitalWrite(13,LOW);
    delay(50);
    digitalWrite(13,HIGH);
    delay(50);
    digitalWrite(13,LOW);
    delay(50);

    wdt_enable(WDTO_4S);

  }
  void loop() {
    digitalWrite(13,HIGH);
    delay(500);
    digitalWrite(13,LOW);
    delay(500);
    //wdt_reset();
   }

Answer 3

I got the WDT working in my Nano with the old bootloader using this code from an old post on Arduino Forum.

The code is added after the wdt_reset();

  //reset watchdog
  wdt_reset();
  //set up WDT interrupt
  WDTCSR = (1 << WDCE) | (1 << WDE);
  //Start watchdog timer with 4s prescaller
  WDTCSR = (1 << WDIE) | (1 << WDE) | (1 << WDP3) | (1 << WDP0);

Answer 4

After that leds on board start to flicker non stop, and data stop posting on serial monitor

Definitely have a read of the datasheet for the '328p, section 11.8. There are several modes of operation - it can interrupt; reset; or both. Even if it resets, it doesn't reload your initial RAM data, so, for instance, line 2 int k=1; looks like an executable statement but is an initializer and has no effect at reset, and k retains its current value. There are probably other, similar, anomalies that happen when the WDT fires.

You probably don't need to understand the WDT down to its last control-bit but definitely make sure you're using it in the mode you want to be in. It will probably be handy during your testing to have a tiny sketch that just disables the watchdog so you can quickly get your Arduino back for the next test.

Answer 5

The problem may be that the 328 defaults to a Watchdog time of 16mS after a reset- WDP3 = 0, WDP2 = 0, WDP1 = 0, WDP0 = 0 so when it resets and starts your program from the beginning of your code, the program never gets very far. I made a very short recovery program that just invokes noInterrupts(); and load it straight after a power off / on. Then you can load a new program that doesn't use the watchdog.