Clear flag after callback causes stall

[jacky4566]

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https://github.com/arduino-libraries/RTCZero/blob/ac98e3da2809500ae50050e5dee12223461921a6/src/RTCZero.cpp#L115

Is there a reason the flag is cleared after the callback? Seems if you have too long of a callback (2+ seconds) then the RTC will hang the processors. Not sure the exact details but are we safe to clear the flag first then do callback? It would make it more noob friendly.

[drewfish]

If we make that change (clear flag before calling callback), what happens if the callback takes longer to execute than the period of the interrupts? For example if the RTC is setup to interrupt every second but the callback takes more than a second to run.