1 Problem to Solve Develop a virtual machine (VM) / simulator for the SubLC3 instruction set. Call this virtual machine SubLC3VM.

The SubLC3 programming language is described in Appendix A. SubLC3VM consists of the following two phases:

1.1 Load Phase

Load the SubLC3 program, which is saved on an external file called mySubLC3, into the memory. Use an array of size MAX_MEMORY_SIZE = 500 to store the instructions.

Fetch-execute-cycle Phase

Execute the program using the following steps: initialize the program counter repeat

fetch the instruction pointed by the counter increment the counter

decode the instruction execute the instruction

end when operation = HALT

2 Input 1. Test the virtual machine thoroughly. You may start testing your program by using the sample SubLC3 program given in Appendix A. Name the input file mySubLC3.txt. A file can contain one large SubLC3 program consisting of different sections. The whole program ends with one HALT statement.

Store the input file in the same location as that of your program file. In your program, open the input file using the path "src\\vmPackage\\mySubLC3.txt"

3 Output 1. Display your name and class information, a line of asterisks (*), the SubLC3 source file, a line of asterisks (*), and finally the result of the SubLC3 execution.

The output must be well formatted and readable.

4 Naming of the Program Modules

Use the following names for your program modules:

Module

Name

Java Project

VmProject

Package

vmPackage

Class

VirtualMachine

Input file

mySubLC3.txt

6 Introduction to SubLC3

The SubLC3 instructions are divided into three different categories: operation, data movement, and control.

Each instruction except for the comment line (which starts with a semicolon) and a label line (which is an identifier) has the following format:

Operator Operands

Hence, a line which does not start with either a semicolon or an operator is a label.

7 Operation Instructions

7.1 ADD Destination Source1 Source2

ADD accepts two integer values, Source1 and Source2, and stores their sum in the Destination variable, Destination.

Each Source can be either a variable or an integer constant.

Examples:

Code:

; Add 3 to the value of num1 and store the result in sum

ADD sum num1 3

Code:

; Add the values of num1 and num2 and store the result in sum

ADD sum num1 num2

Code:

; Add 40 and 6 and store the result in sum

ADD sum 40 6

7.2 SUB Destination Source1 Source2

SUB accepts two integer values, Source1 and Source2, and stores the result of (Source1 Source2) in the Destination variable, Destination.

Each Source can be either a variable or an integer constant.

7.3 MUL Destination Source1 Source2

MUL accepts two integer values, Source1 and Source2, and stores the result of (Source1 * Source2) in the Destination variable, Destination.

Each Source can be either a variable or an integer constant.

7.4 DIV Destination Source1 Source2

DIV accepts two integer values, Source1 and Source2, and stores the result of (Source1 / Source2) in the Destination variable, Destination.

Each Source can be either a variable or an integer constant.

7.5 IN Variable

Inputs an integer value and stores it in Variable.

Example:

Code:

; Input an integer value and store it in the variable num

IN num

7.6 OUT Value

Display Value.

Value can be either an integer variable or a string of characters enclosed in quotation marks (" ")

Example:

Code:

; Display the value of the variable sum

OUT sum

If the value of sum is 1234, the output will be

1234

Code:

; Display Hello World!

OUT "Hello World!"

8 Data Movement Instructions

8.1 STO Destination Source

The STO instruction stores the value of Source in Destination variable. Source can be either a variable or an integer constant.

Example:

Code:

; Store 23 in age

STO age 23

Code:

; Store the value of num2 in num1

STO num1 num2

9 Control Instructions

9.1 BRn Variable Label

If the value of Variable is negative, jump to Label.

Example:

Code:

; If the value of age is negative, jump to sumLabel

BRn age sumLabel

; Other statements sumLabel

; Other statements

9.2 BRz Variable Label

If the value of Variable is zero, jump to Label. Example:

Code:

; If the value of age is zero, jump to sumLabel

BRz age sumLabel

; Other statements sumLabel

; Other statements

9.3 BRp Variable Label

If the value of Variable is positive, jump to Label. Example:

Code:

; If the value of age is positive, jump to sumLabel

BRp age sumLabel

; Other statements sumLabel

; Other statements

9.4 BRzp Variable Label

If the value of Variable is zero or positive, jump to Label. Example:

Code:

; If the value of age is zero or positive, jump to sumLabel

BRzp age sumLabel

; Other statements sumLabel

; Other statements

9.5 BRzn Variable Label

If the value of Variable is zero or negative, jump to Label. Example:

Code:

; If the value of age is zero or negative, jump to sumLabel

BRzn age sumLabel

; Other statements sumLabel

; Other statements

9.6 JMP Label

Jump to Label. Example:

Code:

; Jump to sumLabel

JMP sumLabel

; Other statements sumLabel

; Other statements

9.7 HALT

End the program execution.

10 Comments, Labels and Identifiers

Comment:

Semicolon (;) at the beginning of a line indicates a comment line, which will be ignored by SubLC3VM.

10.1 Identifier:

The name of an identifier starts with a letter, followed by a sequence of zero or more letters, digits or underscores.

An identifier may represent either a variable (of type integer) or a label.

10.2 Label:

Label is an identifier, which indicates a location within the SubLC3 program. It is used as a destination for a JMP or BRx instruction.

11 An Example Program in SubLC3

; Display a sequence of numbers in reverse order

;

; Initialize the values STO increment 2

OUT "Enter the initial number:" IN number

;

; Display the values OUT "The values are:"

SUB tempNum number 1 loopStart

BRn tempNum loopEnd OUT number

SUB number number increment SUB tempNum number 1

JMP loopStart loopEnd

;

; Test the last value of number OUT "The last value of number is OUT number

BRzp number ifEnd

OUT "The last value of number is negative. JMP ifEnd

OUT "The last value of number is not negative. ifEnd

;

OUT "H A V E A N I C E D A Y !" HALT

12 The Equivalent Program in Java

// Display a sequence of numbers in reverse order Scanner scan = new Scanner(System.in);

// Initialize the values

int number;

int increment = 2;

System.out.println("Enter the initial number:"); number = scan.nextInt();

// Display the values System.out.println("The values are:"); while (number >= 1){

System.out.println(number); number = number - increment;

}

// Test the last value of number System.out.println("The last value of number is"); System.out.println(number);

if (number < 0)

System.out.println("The last value of number is negative.");

else

System.out.println("The last value of number is not negative."); System.out.println("H A V E A N I C E D A Y !");

13 Sample execution of the program

Enter the initial number: 5

The values are: 5

3

1

The last value of number is

-1

The last value of number is negative. H A V E A N I C E D A Y !

14 Summary of SubLC3 Statements

Statement

Description

ADD Destination Source1

ADD accepts two integer values, Source1 and Source2, and stores their sum in the Destination variable, Destination.

Each Source can be either a variable or an integer constant.

BRn Variable Label

If the value of Variable is negative, jump to Label.

BRp Variable Label

If the value of Variable is positive, jump to Label.

BRz Variable Label

If the value of Variable is negative, jump to Label.

BRzn Variable Label

If the value of Variable is zero or negative, jump to Label.

BRzp Variable Label

If the value of Variable is zero or positive, jump to Label.

Comment

Semicolon (;) at the beginning of a line indicates a comment line, which will be ignored by SubLC3VM.

DIV Destination Source1 Source2

DIV accepts two integer values, Source1 and Source2, and stores the result of (Source1 / Source2) in the Destination variable, Destination.

Each Source can be either a variable or an integer constant.

HALT

End the program execution.

Identifier

The name of an identifier starts with a letter, followed by a sequence of zero or more letters, digits or underscores.

An identifier may represent either a variable (of type integer) or a label.

IN Variable

Inputs an integer value and stores it in Variable.

JMP Label

Jump to Label.

Label

Label is an identifier, which indicates a location within the SubLC3 program. It is used as a destination for a JMP or BRx instruction.

MUL Destination Source1 Source2

MUL accepts two integer values, Source1 and Source2, and stores the result of (Source1 * Source2) in the Destination variable, Destination.

Each Source can be either a variable or an integer constant.

OUT Value

Display Value.

Value can be either an integer variable or a string of characters enclosed in quotation marks (" ")

STO Destination Source

The STO instruction stores the value of Source in Destination variable.

Source can be either a variable or an integer constant.

SUB Destination Source1 Source2

SUB accepts two integer values, Source1 and Source2, and stores the result of (Source1 Source2) in the Destination variable, Destination.

Each Source can be either a variable or an integer constant.

15 Reference

These instructions are adapted from the LC3 instruction set: http://www.lc3help.com/tutorials.htm?article=Basic_LC-3_Instructions/