Wait for the board’s built-in button (labeled BUT on the silkscreen) to be pressed, possibly with timeout.
Wait until the button is pressed and released, timing out if no press occurs.
The button pin must have its mode set to INPUT. This can be accomplished portably over all LeafLabs boards by calling pinMode(BOARD_BUTTON_PIN, INPUT).
Parameters
Number of milliseconds to wait until the button is pressed. If timeout_millis is 0, wait forever.