Yansong,

It would suggest it may be better to write the software such that it is
independent of time key is pressed. ie. act on keypress but don't respond to
further key presses until original key is released.

You also normally debounce the key with a small delay (30-50ms maybe).

ie. If keypress detected wait 30ms
    if key still being pressed, act
    wait till key released
    small delay

Regards

David Huisman

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