From Gamebuino Wiki
Function used to trigger a repetitive action at a given period when a button is held down.
- button (byte): the identifier of the button, to choose from
BTN_A, BTN_B, BTN_C, BTN_UP, BTN_RIGHT, BTN_DOWN, BTN_LEFT
- duration (byte): the duration in number of frames (20 frames per second by default)
- boolean: returns true every <duration> frames when the button is held down