I don't understand this bug

Projects Programming
1

I want to calculate the duration of a loop and use this value in my code. Hovewer the result (I called 'timeloop") gived me often 0 because the code is short, so I would like to constrain this value with minimum 1 with the code :
timeloop = max(millis() - timeprev , 1);

But in this example below, instead to have a Serial.print every second, I have the serial.print "timeloop = 1" every millisecond in the monitor like if the command 'mytimer += timeloop;' was broken.

Also if I add a delay(1) at the end, the code works correctly.
I tried also this formula without good result :
timeloop = max(millis() - long(timeprev),long(1));

The code :

unsigned long timeprev;
unsigned long timeloop;
int mytimer ;

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

void loop()
{
  timeloop = max(millis() - timeprev , 1);  
  timeprev = millis();
    
  if(mytimer > 1000)
  { 
  
    Serial.print("timeloop = ");
    Serial.println(timeloop);
    Serial.println("--------------");
      
    mytimer = 0;
  
  }
  else
  {
    mytimer += timeloop;
  }
    
}
2

Why not use micros()?

3

I don't need to be so accurate, also the main problem is that I don't understand why it dont work and it makes me mad.

4

Your loop() runs with very high speed. There is no limit for the speed. It runs faster than once per millisecond. That means that "mytimer += timeloop" is executated very often, and the 1000 is reached before you know it.

Why not measure it like everyone does:

unsigned long t1, t2, t;
t1 = micros();
....  // here the code to test
t2 = micros();
t = t2 - t1;
5

"I want to calculate the duration of a loop"

I wouldn’t be surprised if your loop() runs in tens of microseconds.

Use Nick's profile timer:

See ZIP file: http://www.gammon.com.au/Arduino/ProfileTimer.zip

6

If you look at the reference for the max(), it gives you this warning:

Because of the way the max() function is implemented, avoid using other functions inside the brackets, it may lead to incorrect results