Programming Model $3$

Introduction

Objectives

At the end of this lab you should be able to:

$$ Explain how common program variables are stored

$$ Distinguish between different types of high$-$level program

statements

$$ Understand low$-$level code corresponding to program

statements

$$ Explain how program subroutines work

$$ Use the simulator to create user interrupts

Processor $($CPU$)$ Simulators

The computer architecture tutorials are supported by simulators, which

are created to underpin theoretical concepts normally covered during

the lectures. The simulators provide visual and animated

representation of mechanisms involved and enable the students to

observe the hidden inner workings of systems, which would be difficult

or impossible to do otherwise. The added advantage of using

simulators is that they allow the students to experiment and explore

different technological aspects of systems without having to install and

configure the real systems.

Basic Theory

High$-$level language $($HLL$)$ programs are made of variables holding

data values and multiple program statements as algorithms. These

statements often control the flow of program execution under certain

conditions. Calls to subroutines and interrupts all change the sequential

flow of a program execution without which feature programs would not

do any useful work.

Simulator Details

This section includes some basic information on the simulator, which

should enable the students to use the simulator. The tutor$($s$)$ will be

available to help anyone experiencing difficulty in using the simulator.

The simulator for this lab is an application running on a PC and is

composed of multiple windows.

$1$

Image $1-$ Main simulator window

The main window shown in Image $1$ is composed of several sub$-$views, which

represent different functional parts of the simulated processor. For this lab

session we are interested only in the compiler part of the simulator.

In order to access the compiler, click on the

COMPILER... button as shown in Image $2$

on the right. The compiler window shown in

Image $3$ below will show.

Image $2-$ Advanced functions

$2$

Image $3-$ The main compiler window

In the compiler window there are three main sub$-$windows

$$ Program Source $-$ all high$-$level source statements appear here.

$$ Compiler Progress $-$ information on the progress of a compilation

appear here.

$$ Program Code $-$ assembly code generated by the compiler appear

here.

Lab Exercises $-$ Investigate and Explore

The lab exercises are a series of experiments, which are attempted by

the students under guidelines. The students are expected to carry out

further investigations on their own in order to form a better

understanding of the technology.

Now, have a go at the following activities:

$1.$ Enter the following source code and compile it$.$

$3$

program Test$1$

var IntVar integer

var BoolVar boolean

var StrVar$1$ string $(5)$

var StrVar$2$ string$(20)$

IntVar $=6$

BoolVar $=$ true

StrVar$1=$ "Hello"

StrVar$2=$ "And again"

end

Now click on the SYMBOL TABLE... button. The Symbol Table

window will show. Observe the kind of information kept in the symbol

table. Make a note of the type, size and address fields for each of the

entries in the table.

Next, load the compiled program in memory. In the CPU simulator

window click on the SHOW PROG MEMORY... button. The contents of

the program data memory will show. Make sure it stays on top. Then

run the program at maximum speed. Observe the contents of the

memory paying attention to the address locations you noted before.

$2.$ Enter the following source statements

Program Test$2$

n $=0$

i $=$ n $+1$

p $=$ i $*3$

writeln $($ n$=,$ n$,$ i$=,$ i$,$ p$=,$ p$)$

end

Compile the above program. Now observe the code generated in the

PROGRAM CODE window. You don$$t need to analyse it in detail.

However, count the number of jump instructions $($i$.$e$.$ those that start

with a letter $$J$)$ and note this down. Can you tell what kind of program

statements this program is using?

$3.$ Enter the following source statements

Program Test$3$

n $=0$

if n $<mtext></mtext><mn>5</mn>$ then

p $=$ p $+1$

end if

end

$4$

Compile the above program. Now observe the code generated. How

many jump instructions are there? What do you think is the purpose of

the jump instruction in this code? What kind of a statement is an $$if$$

statement?

$4.$ Enter the following source statements

program Test$4$

p $=1$

for n $=1$ to $10$

p $=$ p $*2$

next

end

Compile the above program. Now observe the code generated. How

many jump instructions are there? What do you think is the purpose of

each of the jump instructions in this code? What kind of a statement is

a $$for$$ statement? Can you think of another statement of this kind $($you

can give an example from any programming language you are familiar

with$)?$

$5.$ Enter the following source statements

Program Test$5$

sub One

writeln$($I am sub One$)$

end sub

sub Two

call One

writeln$($I am sub Two$)$

end sub

call Two

End

Compile the above program. Next, load the compiled program in

memory. In the CPU simulator window click on the SHO