function init() {
  comment("init");
  A('256');
  C('D=A');
  compToReg('SP', 'D');    // SP=256
  cmdCall('Sys.init', 0);  // call Sys.init()
}

// Sys.vm for NestedCall test.
//
// Copyright (C) 2013 Mark A. Armbrust.
// Permission granted for educational use.

// Sys.init() calls Sys.main(), stores the return value in temp 1,
//  and enters an infinite loop.

function Sys.init 0
call Sys.main 0
pop temp 1
label LOOP
goto LOOP

// Sys.main() calls Sys.add12(123) and stores return value (135) in temp 0.
// Returns 456.

function Sys.main 0
push constant 123
call Sys.add12 1
pop temp 0
push constant 246
return

// Sys.add12(int x) returns x+12.
// It allocates 3 words of local storage to test the deallocation of local
// storage during the return.

function Sys.add12 3
push argument 0
push constant 12
add
return

// 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 of basic system services.
 */
class Sys {

    /** Performs all the initializations required by the OS. */
    function void init() {
        do Math.init();
        do Output.init();
        do Screen.init();
        do Keyboard.init();
        do Memory.init();
        do Main.main();
    }

    /** Halts execution. */
    function void halt() {
        while(true){}
    }

    /** Waits approximately duration milliseconds and then returns. */
    function void wait(int duration) {
        var int i, j;
        let i = 0;
        while( i < duration ) {
            let j = 0;
            while( j < 200 ) {
                let j = j + 1;
            }
            let i = i + 1;
        }
    }

    /** Prints the given error code in the form "ERR<errorCode>", and halts. */
    function void error(int errorCode) {
        do Output.printString("Err");
        do Output.printInt(errorCode);
        do halt();
    }
}