SDD Translation

12 Software Design and Development

Implementation

TRANSLATION


Syllabus

Different Methods include: Translation Incremental Compilation Interpretation

Advantages and disadvantages of each method

The translation process.


Why Study the CPU?

What does the CPU do? Is the brains of the computer. Reads and executes program instructions. Performs calculations and makes decisions

(Processing). Also responsible for the detection of syntax

and run-time errors within programs.


Why Study the CPU?

Components of the CPU

ALU – The arithmetic logic unit and all arithmetic computations take place , such as addition, multiplications and all comparison operations.

Control Unit – Looks after the fetch-execute cycle to make sure it working effectively.


Why Study the CPU?

Components of the CPU

Accumulator – A special storage register associated with the ALU which is used to store the results of instructions during processing.

Program Counter – Is a register that holds the address of the next instruction.

Register – A special storage location used for temporary storage of data.


Hierarchy of Code Translation

Source Code

Assembly Code

Machine Code

Opcode Operand Operand

Instruction Address Data


What is Machine Code?

Is the language of a computer system and that of the CPU.

Known a the binary system. Each computer instruction is a string of binary

digits.

E.G. 100100 100010101100100111111


Fetch-Execute Cycle

1. Fetch (Where to Go?) Instructions are fetched from main memory. The location of the next instruction is stored within

a program register called the Program Counter.


Fetch-Execute Cycle

2. Decode (What to do?) Separation of the machine code into an opcode

and two operands take place. The opcode is then loaded into the instruction

register.


Fetch-Execute Cycle

3. Execute (Carry out instructions) The opcode is sent to and executed by the ALU.


Fetch-Execute Cycle

4. Store(Copy the result) Results during processing are stored in the

accumulator. Once processing is complete results are then sent

to main memory.


Processing Instructions

Sum = Total + Number

Source Code

// Assume Sum is at address 101// Assume Total is at address 134// Assume Number is at address 135

0. LOAD A 1341. LOAD B 1352. DIV4. SAVE C 1015. STOP

Assembly Code

Machine Code

10110 10001111 111010000110

10110 11101111 101010000110

10000 10101111 100010000110

11110 10000011 100111100110

10100 11101111 100000000000

00110 11001111 100010001110


Translation

Why does it occur? Computers cannot understand machine code.

Source Code

Machine Code

Translator


Translation Process

1. Interpreter Source code is translated line by line and

immediately executed. If errors exist they will cause an immediate halt.

German sentence is spoken. INTERPRETER

GERMAN ENGLISH

English sentence is spoken.

Interpreter translates message from German to English.


Translation Process

2. Compilation Known as ‘Batch Processing’ as an entire

executable file is created. All errors are recorded and sent at the end. If changes are required then recompilation will be

required.

TRANSLATOR ENGLISH

The translator converts the German in a novel for English


Translation Process

3. Incremental Compilation The aim is to reduce the time spent recompiling. Incremental compilers aim to reduce the

translation time by only recompiling those parts of code that have changed since the last compile took place.

TRANSLATOR

The translator converts the new changes into a new edition.

1st Edition

Changes

2nd Edition


Translation Process in Detail

LexicalAnalysis

SyntacticalAnalysis

CodeGeneration

Object Code

Error File

Source CodeHigh Level Code

Error

Series of Tokens

Error

SyntacticallyCorrect Tokens

Machine Code


Lexical Analysis

Requires the source code to be read one character at a time.

Each character is scanned and redundant characters such as remarks, spaces and indentation are removed.

Variables, constants, operators, strings of text and control structures are labelled with a token.

Most translators have a token dictionary.


Lexical AnalysisToken Type

& VARIABLE

@ BEGIN

# END

$ IF

? THEN

{} ELSE

[] ENDIF

<> OPERATOR

:: GET

() PRINT

% CONSTANT

!! STRING

Given the Following Source Code:

BEGIN

Get Number

IF Number > 10 THEN

Print OK

ELSE

Print No

ENDIF

END

What would be the tokens?


Lexical Analysis

ANSWER

@

:: &

$ & <>% ?

() !!

{}

() !!

[]

#


Syntactical Analysis

The tokens are then passed through the syntactic analyser to determine the logic of the code.

The syntactic analysis involves an examination of whether the identified elements in the statements are legal according to the syntax of the language.

This process is best understood by a Parse Tree.



Parse Tree

Selection

IF Condition Then Statement

Variable Operator Constant

Else Statement

String String



Parse Tree

Selection

IF Condition Then Statement

Variable Operator Constant

Else Statement

String String

Number

&

>

<>

10

%

Print OK

() !!

Print No

()!!


Production of Machine Code

This undertaken when the processes of lexical and syntactical analysis have been completed an no errors found.

This stage involves converting each token into their respective machine code instructions.

All characters in strings are converted to binary code using their ASCII values.

Tokens are collected left to tight from the parse tree in a method called transversing.


Production of Machine Code

This undertaken when the processes of lexical and syntactical analysis have been completed an no errors found.

This stage involves converting each token into their respective machine code instructions.

All characters in strings are converted to binary code using their ASCII values.

Tokens are collected left to tight from the parse tree in a method called transversing.


Translation Tools1. LINKER Does what the name suggests it links the main line

to all the other sub modules.

2. LOADER This is the component of the translator that loads

the module from main memory.

3. OPTIMISER Used to reduce redundant code for quick execution

Technology

SDD Translation