eceg431/12/Sys.jack

// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/12/Sys.jack

/**
 * A library that supports various program execution services.
 */
class Sys {

    /** Performs all the initializations required by the OS. */
    function void init() {
        // do Memory.poke(8000, 1); // Start
        do Memory.init();
        // do Memory.poke(8000, 2); // Mem init done
        do Math.init();
        // do Memory.poke(8000, 3); // Math init done
        do Screen.init();
        do Output.init();
        do Keyboard.init();
        do Main.main();
        do Sys.halt();
        return;
    }

    /** Halts the program execution. */
    function void halt() {
        while (true) {}
        return;
    }

    /** Waits approximately duration milliseconds and returns.  */
    function void wait(int duration) {
        var int i, j;
        let i = 0;
        
        while (i < duration) {
             let j = 0;
             // Calibration: loop count determines delay.
             // On typical VM emulator settings (Fast), ~50-100 loops might be 1ms?
             // "WaitWithInput" sample in Snake used loop for waiting.
             
             while (j < 50) {
                 let j = j + 1;
             }
             let i = i + 1;
        }
        return;
    }

    /** Displays the given error code in the form "ERR<errorCode>",
     *  and halts the program's execution. */
    function void error(int errorCode) {
        do Output.printString("ERR");
        do Output.printInt(errorCode);
        do Sys.halt();
        return;
    }
}