How to get the cause of reset in arduino uno

Hi, I am using an Arduino Uno and I need to evaluate what has been the cause of the reset, I am using this code but I always have the register MCUSR value equal to 2, what could be my error?

void setup() {
  Serial.print("MCUSR: ");

  if (MCUSR & (1 << PORF)) {        // Power-on Reset
    Serial.println("Cause of Reset = Power-on Reset" );
  else if (MCUSR & (1 << EXTRF)) {  // External Reset
    Serial.println("Cause of Reset = External Reset" );
  else if (MCUSR & (1 << BORF)) {   // Brown-Out Reset
    Serial.println("Cause of Reset = Brown-Out Reset" );
  else if (MCUSR & (1 << WDRF)) {   // Watchdog Reset
    Serial.println("Cause of Reset = Watchdog Reset" );
  MCUSR = 0;

void loop() {

How are you stimulating this sketch to reset in all the ways you want it to recognize?

What do you expect for the output?


The bootloader runs before your sketch, and resets the flag for the cause of the reset. Optiboot can pass the data to your code, but you need a more recent version than the one shipped on the UNO.

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Please can you give more details on how to achieve this

Did you research it? Optiboot must be documented...

Does not help that the old example code of test_reset.ino seems to no longer exist.
This looks like the current example code, note that it REQUIRES a newer version of optiboot than the standard one on an UNO.

You could just remove the bootloader entirely and load your sketch using an ISP, then you do not have to worry about optiboot messing with MCUSR.

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