How millis() resets itself to 0











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Looking at the documentation for the millis() function , it says:




Returns the number of milliseconds since the Arduino board began
running the current program. This number will overflow (go back to
zero), after approximately 50 days.




How's this possible? Is Arduino detecting when millis() overflow then resets the value to 0? If so, how does it do it? I just want to know what exactly is going on under the hood with the variable that is being returned by the millis() function.










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    up vote
    8
    down vote

    favorite












    Looking at the documentation for the millis() function , it says:




    Returns the number of milliseconds since the Arduino board began
    running the current program. This number will overflow (go back to
    zero), after approximately 50 days.




    How's this possible? Is Arduino detecting when millis() overflow then resets the value to 0? If so, how does it do it? I just want to know what exactly is going on under the hood with the variable that is being returned by the millis() function.










    share|improve this question
























      up vote
      8
      down vote

      favorite









      up vote
      8
      down vote

      favorite











      Looking at the documentation for the millis() function , it says:




      Returns the number of milliseconds since the Arduino board began
      running the current program. This number will overflow (go back to
      zero), after approximately 50 days.




      How's this possible? Is Arduino detecting when millis() overflow then resets the value to 0? If so, how does it do it? I just want to know what exactly is going on under the hood with the variable that is being returned by the millis() function.










      share|improve this question













      Looking at the documentation for the millis() function , it says:




      Returns the number of milliseconds since the Arduino board began
      running the current program. This number will overflow (go back to
      zero), after approximately 50 days.




      How's this possible? Is Arduino detecting when millis() overflow then resets the value to 0? If so, how does it do it? I just want to know what exactly is going on under the hood with the variable that is being returned by the millis() function.







      millis






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      asked Nov 25 at 7:58









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          It is not a property of millis(). Every counter with limited number of digits once returns to zeros. For example a 4 digits tally counter returns to zeros after 9999.



          Under the hood the variable for millis() is of type unsigned long which is 32 bits on the Arduino. Here the 32 bits are the digits of the tally counter. With only two digits of binary 0 and 1. The maximum is 11111111 11111111 11111111 11111111. After then it returns to zeros if adding 1. The 32 ones is 2^32 - 1, or 4294967295 in decimal. The maximum value for the counter is then 4294967295 milliseconds. Converted to days you get approximately 49.71 days.



          And now, you know how computers work. Thousands of binary tally counters.



          enter image description here






          share|improve this answer



















          • 2




            Old versions of Windows also maintained a milliseconds count in a 32-bit integer, causing lots of software to misbehave after 49 days uptime.
            – Russell Borogove
            Nov 26 at 2:18











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          up vote
          18
          down vote



          accepted










          It is not a property of millis(). Every counter with limited number of digits once returns to zeros. For example a 4 digits tally counter returns to zeros after 9999.



          Under the hood the variable for millis() is of type unsigned long which is 32 bits on the Arduino. Here the 32 bits are the digits of the tally counter. With only two digits of binary 0 and 1. The maximum is 11111111 11111111 11111111 11111111. After then it returns to zeros if adding 1. The 32 ones is 2^32 - 1, or 4294967295 in decimal. The maximum value for the counter is then 4294967295 milliseconds. Converted to days you get approximately 49.71 days.



          And now, you know how computers work. Thousands of binary tally counters.



          enter image description here






          share|improve this answer



















          • 2




            Old versions of Windows also maintained a milliseconds count in a 32-bit integer, causing lots of software to misbehave after 49 days uptime.
            – Russell Borogove
            Nov 26 at 2:18















          up vote
          18
          down vote



          accepted










          It is not a property of millis(). Every counter with limited number of digits once returns to zeros. For example a 4 digits tally counter returns to zeros after 9999.



          Under the hood the variable for millis() is of type unsigned long which is 32 bits on the Arduino. Here the 32 bits are the digits of the tally counter. With only two digits of binary 0 and 1. The maximum is 11111111 11111111 11111111 11111111. After then it returns to zeros if adding 1. The 32 ones is 2^32 - 1, or 4294967295 in decimal. The maximum value for the counter is then 4294967295 milliseconds. Converted to days you get approximately 49.71 days.



          And now, you know how computers work. Thousands of binary tally counters.



          enter image description here






          share|improve this answer



















          • 2




            Old versions of Windows also maintained a milliseconds count in a 32-bit integer, causing lots of software to misbehave after 49 days uptime.
            – Russell Borogove
            Nov 26 at 2:18













          up vote
          18
          down vote



          accepted







          up vote
          18
          down vote



          accepted






          It is not a property of millis(). Every counter with limited number of digits once returns to zeros. For example a 4 digits tally counter returns to zeros after 9999.



          Under the hood the variable for millis() is of type unsigned long which is 32 bits on the Arduino. Here the 32 bits are the digits of the tally counter. With only two digits of binary 0 and 1. The maximum is 11111111 11111111 11111111 11111111. After then it returns to zeros if adding 1. The 32 ones is 2^32 - 1, or 4294967295 in decimal. The maximum value for the counter is then 4294967295 milliseconds. Converted to days you get approximately 49.71 days.



          And now, you know how computers work. Thousands of binary tally counters.



          enter image description here






          share|improve this answer














          It is not a property of millis(). Every counter with limited number of digits once returns to zeros. For example a 4 digits tally counter returns to zeros after 9999.



          Under the hood the variable for millis() is of type unsigned long which is 32 bits on the Arduino. Here the 32 bits are the digits of the tally counter. With only two digits of binary 0 and 1. The maximum is 11111111 11111111 11111111 11111111. After then it returns to zeros if adding 1. The 32 ones is 2^32 - 1, or 4294967295 in decimal. The maximum value for the counter is then 4294967295 milliseconds. Converted to days you get approximately 49.71 days.



          And now, you know how computers work. Thousands of binary tally counters.



          enter image description here







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Nov 25 at 11:35

























          answered Nov 25 at 8:27









          Juraj

          6,4002925




          6,4002925








          • 2




            Old versions of Windows also maintained a milliseconds count in a 32-bit integer, causing lots of software to misbehave after 49 days uptime.
            – Russell Borogove
            Nov 26 at 2:18














          • 2




            Old versions of Windows also maintained a milliseconds count in a 32-bit integer, causing lots of software to misbehave after 49 days uptime.
            – Russell Borogove
            Nov 26 at 2:18








          2




          2




          Old versions of Windows also maintained a milliseconds count in a 32-bit integer, causing lots of software to misbehave after 49 days uptime.
          – Russell Borogove
          Nov 26 at 2:18




          Old versions of Windows also maintained a milliseconds count in a 32-bit integer, causing lots of software to misbehave after 49 days uptime.
          – Russell Borogove
          Nov 26 at 2:18


















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