question: public void queueShieldFrame ( ShieldFrame frame ) { if ( frame == null ) throw new NullPointerException ( "The passed frame is null, have you checked its validity?" ) ; if ( ! isConnected ( ) ) { onError ( OneSheeldError . DEVICE_NOT_CONNECTED ) ; return ; } else if ( isUpdatingFirmware ( ) ) { onError ( OneSheeldError . FIRMWARE_UPDATE_IN_PROGRESS ) ; return ; } queuedFrames . add ( frame ) ; callbackEntered ( ) ; }
target:  Explicitly queue a shield frame for sending after the Arduino exits the callback.