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I was just curious about how the AVR architecture manages errors that would cause a regular desktop program to crash. I'm talking about logical errors for example math problems that are undefined. Such as division by 0 and getting a square root of a negative number. At first I was expecting that by giving an error to the AVR chip it will just return 0. But I ran this program:

void setup() {

Serial.begin(9600);

}

void loop(){

int x = 0;

int p = 50;

int result;

result = p/x;

Serial.println(result);

result = sqrt(-10);

delay(1000);

Serial.println(result);

delay(10000);

}

and got this output:

4294967295

0

After this I got really confused. Why would the result variable take the maximum value of an unsigned long? Since I declared an int the micro controller must have dedicated 2 bytes of dynamic memory to this variable but apparently it somehow managed to get additional 2 bytes to store the data. Could this mean that the AVR chip can corrupt data in other memory locations while allocating new data for the variable that just was fed a undefined in to it? Okay maybe the AVR chip just sets any mathematical nonsense to 4294967295. But no in the example of getting the square root of -10 we see that the value became 0. Although this is probably a function processed by some library so maybe there is some kind of protection against these errors. Also, I tried to run the program above but with a byte variable for the result instead of int.

void setup() {

Serial.begin(9600);

}

void loop(){

int x = 0;

int p = 50;

int result;

result = p/x;

Serial.println(result);

result = sqrt(-10);

delay(1000);

Serial.println(result);

delay(10000);

}

And the result was the same. So, is there some kind of documentation about error management in AVR since this is important to know while development.

P.S. Everything was run on a real Atmega 328p chip on an arduino nano.

The simple answer is: they are not handled at all.

According to the C and C++ standards, what you are invoking is called
undefined behavior, meaning anything can happen. In practical
terms, it means that the compiler can do its optimizations assuming
you will never invoke undefined behavior, and completely disregard what
could happen if the assumption does not hold. The generated code could
be completely broken, it won't be the compiler's fault.

The AVR architecture cannot do divisions, nor floating point math. Thus
all the errors you have here happen at the software level. Note that
sqrt(-10) is not an error (it's NaN, which is correctly handled by
the avr-libc), but converting that to an int (which you do when you
assign it to result) is an error.

If you really want to know the details of what happens with each of
these errors, there is only one option: you have to disassemble the
executable program and read the assembly listing.