Is Chrono reliably working past millis() rollback/overflow (+47days) ? about chrono HOT 2 CLOSED

By default it uses the basic millis() function. However you can use a function pointer instead so you could design your own timing function using a RTC for example.

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Because of overflow math, the timer should function properly. Here is an explanation:

Chrono uses the following code (millis() - previous_millis >= interval_millis) to calculate if a Chrono has passed a certain interval.

The maximum value for an unsigned long is 4,294,967,295. If you add 1 to 4,294,967,295, you rollover to 0. If you subtract 1 to 0, you get 4,294,967,295.

For an actual example, lets say that previous_millis = 4,294,967,200 and interval_millis = 100:

• If millis() is 4,294,967,250, millis() - previous_millis gives (4,294,967,250 - 4,294,967,200) = 50 and the function will return false (i.e. has not passed the interval of 100)
• Once millis() overflows and reaches 0, millis() - previous_millis returns (0 - 4,294,967,200) = -4,294,967,200 = 96 with overflow and will return false (i.e. has not passed the interval)
• Once millis() reaches 4, millis() - previous_millis returns (4 - 4,294,967,200) = -4,294,967,196 = 100 with overflow and this will return true (i.e. has passed the interval)

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