# IJVM-Intro

```MIC-1 SIMULATOR
Programming in IJVM
Computer Architecture
Jim Skon
Topics

Mic-1 simulator programming
◦ http://www.ontko.com/mic1/
◦ Programming assignment on Moodle
Reverse Polish notation
 Assembly language
 IJVM instruction set

Using the Mic-1 Simulator
Runs as a Java Application
 Simulates a simplified version of the Java
Virtual Machine.
 Two Versions

◦ High resolution
◦ Low resolution
Using the Mic-1 Simulator






Write IJVM “.jas” files using an editor –
Start the Mic-1 simulator
Load and Assemble the “.jas” file using the
IJVM assembler. Use the “File/Assemble/
This creates machine code.
Example: acsii.jas
◦ Prints all characters!
Reverse Polish Notation (RPN)

Method to write arithmetic expressions
◦ Avoids the use of brackets to define priorities for
evaluation of operators

Devised by Jan Lucasiewicz
◦ Polish philosopher and mathematician
◦ In his notation, the operators preceded their
arguments
◦ The “reverse” places operators after arguments
http://wwwstone.ch.cam.ac.uk/documentation/rrf/rpn.ht
ml
 http://en.wikipedia.org/wiki/Reverse_Polish_No
tation


RPN Example
(3 + 5) * (7 -2)
 Then, subtract 2 from 7
 Finally, multiply the two results together


Using RPN notation: 3 5 + 7 2 -*
RPN Example – Stack based








3 5 + 7 2 -* (read from left to right)
Push 3 onto stack
Push 5 onto the stack – The stack now contains (3, 5)
Use “+” operator – Pop two numbers from stack and
push result (8)
Push 7 onto the stack
Push 2 onto the stack – The stack now contains (8, 7, 2)
Use “-” operator – Pop two numbers from stack and
push result (5)
Use “*” operator – Pop two numbers from stack and
push result (40)
RPN Example – IJVM Code
BIPUSH 3
 BIPUSH 5 – The stack now contains (3, 5)
 IADD – Pop two numbers from stack and
push result (8)
 BIPUSH 7
 BIPUSH 2 – The stack now contains (8, 7, 2)
 ISUB – Pop two numbers from stack and
push result (5)
 IMUL – Pop two numbers from stack and
push result (40)

Structured Computer Organization

Digital logic builds
microarchitecture

Microarchitecture
implements the ISA

ISA is in machine
language

Assembly language
allows us to use ISA
Assembly Language

Uses symbolic names (mnemonics) and
machine language

An assembler converts the assembly
language into machine language

Each statement produces exactly one
machine instruction (1:1 mapping)
Why Use Assembly?

Versus machine language
◦ Easier to remember mnemonics for instructions
◦ Easier to work with the symbolic addresses

Versus high-level language
of the ISA
◦ Performance: Code produced can be much
smaller (for low-memory devices) and faster (for
speed-critical functions)
Undocumented Assembler
Instructions












ARG : Agree to Run Garbage
BDM : Branch and Destroy Memory
CMN : Convert to Mayan Numerals
DDS : Damage Disk and Stop
ETO : Emulate Toaster Oven
FSE : Fake Serious Error
GSI : Garble Subsequent Instructions
GQS : Go Quarter Speed
HEM : Hide Evidence of Malfunction
IDD : Inhale Dust and Die
IKI : Ignore Keyboard Input
IJVM Instruction Set
IJVM Instruction Set
Exercise

Write IJVM assembly code for the
following C++ code:
int x = 0;
for (int i = 0; i < 20; i++)
x+= i;
Basic Program Format
.main
// all variables declared within .varand .end-var
.var
x
i
.end-var
// Main program goes next
// Program execution is terminated with a HALT statement
// See next slide for exercise solution
.end-main
Solution to Previous Exercise
BIPUSH 0
ISTORE x
BIPUSH 0
ISTORE I
L1: BIPUSH 19
ISUB
IFLT L2
ISTORE x
IINC i 1
GOTO L1
L2: HALT
Input and Output

IN
◦ Reads a character from the key buffer
◦ Pushes its value onto the stack
◦ If no key has been pressed, zero will be
pushed onto the stack

OUT
◦ Pops a word off the stack
◦ Prints it to the standard output text area
◦ Can only output ASCII values
Getting a Character from Keyboard
GOTO getch
L0:
ISTORE z
HALT
getch: IN
DUP
GOTO L0
GOTO getch
Assignment
Get the ascii.jas, sum.jas, and echo.jas
programs to all work.
 Write a program to read in a two digit
number, and sum the even numbers from
2 to that number.
 Extra credit if you can print out the

```
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