/**
 * This library provides access to BUT and LED.
 */
class GPIO {
 
    /** Initialize LED and BUT. LED is memory mapped to addr.
     *  BUT is memory mapepd to addr +1  */
    function void init(int addr){
    }

    /** Returns the value of LED. */
    function int readLed(){
    }

    /** Write c to LED */
    function void writeLed(int value){
    }

    /** Returns the value of BUT */
    function int readBut() {
    }
}