Measure short amounts of time with micros()

Tested on CC3200.

I am trying to see how long a pin is held in one state, the time will be pretty short at most 100us.

So I tried with micros() before and after, but didnt get good results, then I tried timing a simple pinmode and digitalwrite, that gave a negative or very large value...

So I boiled it down to this example

while(1)
{
  unsigned long i = micros();
  delayMicroseconds(100);
  unsigned long p = micros();  
  unsigned long o = p-i;
  Serial.print("Tooki : ");  Serial.println(i);
  Serial.print("Tookp : ");  Serial.println(p);
  Serial.print("Tooko : ");  Serial.println(o);  
  
  i = micros();
  delayMicroseconds(1000);
  p = micros();  
  o = p-i;
  Serial.print("Tooki : ");  Serial.println(i);
  Serial.print("Tookp : ");  Serial.println(p);
  Serial.print("Tooko : ");  Serial.println(o);  

Serial.println();Serial.println();Serial.println();

delay(1000);  
  
}

I have made a time machine :)

Tooki : 112690699
Tookp : 112690597
Tooko : 4294967194
Tooki : 112693032
Tookp : 112694699
Tooko : 1667

The numbers are stable, the funny part is that i-p is about 100, but p is set to micros() after the sleep of 100micro seconds so it should be lower than i.

If I increase the sleep to 1000(1 mili second if I am not mistaken), then it works correctly

Tooki : 4064995
Tookp : 4065995
Tooko : 1000
Tooki : 4067298
Tookp : 4068995
Tooko : 1697

This is tested in a while loop at the end of the setup function.

I have searched for similar issues but they seemed to relate to using the function in interrupts, if thers another thread on the subject already, please send me in the right direction.