/**
 * Library that provides character based access to UART_TX and UART_RX
 */
class UART {
 
    /** initializes UART. UART_TX is memory mapped at addr.
     *  UART_RX is memory mapped at addr+1 */
    function void init(int addr){
    }

    /** wait until UART_RX receives the next char and return the value. */
    function int readChar() {
    }

    /** wait for UART_TX to be ready to send next byte and send c. */
    function void writeChar(int c){
    }
}