Computer organization & Assembly Language

Programming

Rabie A. Ramadanhttp://www.rabieramadan.org/ Ra.ramadan@uoh.edu.sahttp://www.rabieramadan.org/classes/2014-2015/ICS232/

Class Style Do not think of the exam

Just think of the class materials and how much you learn from it

Feel free to stop me at any time I do not care how much I teach in class as long

as you understand what I am saying

There will be an interactive sessions in class

you solve some of the problems with my help

Chapter 2 — Instructions: Language of the Computer — 2

Chapter 2 — Instructions: Language of the Computer — 3

When the time is up , just let me know….

Textbook

S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.

Grading

Course Objectives To introduce basic concepts of computer

organization.

To illustrate the computer organization concepts by Assembly Language programming.

To teach Assembly language of most recent processor such as Intel Pentium processor.

Outline

A user’s view of computer systems What is assembly language?

Relationship to machine language

Advantages of high-level languages Faster program development Easier maintenance Portability

Chapter 1: Page 7

Why program in assembly language?

Time-efficiency Space-efficiency Accessibility to hardware

Typical applications Why learn assembly language? Performance: C versus assembly

language Multiplication example

What is a Machine ?

In General: Device that processes a series of raw materials into the desired product

following a well-defined process

Machine

Process DirectivesRaw

Material

Final Product

Types of Machines

Device Raw Material Products

Food Processing Factory

Natural Fruits, Vegetables, Meats, Dairy and Spices

Manufactured (Packaged) Food

Products

AirportPlanes, Travelers,

GoodsPlanes, Travelers,

Goods

Administrative Office

Application Files Decisions

Computer Data Data

Computer Machine Model

Machine = Computer

Process = ProgramDirectives

Program = Suite of Instructions

Instruction = Simple Operation

Basic Computer Organization (1)

Need a Unit to Execute Instructions

Need a Unit to Contain Programs

Need a Unit to Contain Input Data

Need a Unit to Contain Intermediate Stage Data

Need a Unit to Input Data Need a Unit to Output Data

Central Processing Unit (CPU)

Memory

IO

Cpu Memory

I/O

Basic Computer Organization (3)

Buses: Groups of Electrical Signals or Wires That Establish The Communication Between The Different Computer System Components

Buses

Memory

0

1

2

Similar to a set of Storage BinsEach Bin is Called:A Memory Location

Each Location has a ContentAnd an Index

The Content is The Data and the Index is The Address

Data is Written in MemoryAnd Read from The MEmory

The CPU Reads Data From MemoryAnd Writes Data Into Memory

Data 1

Data 2

Cpu

I/O

Address Bus

Data Bus

Control Bus

Basic Computer Organization (3)

Address Bus: Specifies the Address of the Data being AccessedData Bus: Carries the Data to be TransferredControl Bus: Specifies the Nature of the Transfer:

(Memory Read/Write or I/O)

Memory

Memory

Storage Device Stores Programs and

Data coded in binary format.

Technically “similar” to a two-dimensional array of “switches”

A “switch” called a bit (abbr. for binary digit)

n Address lines means 2n words of m bits each

0

1

m

n

2n

Data

Address

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Memory

2 Operations: Read: Copy Data

stored in word of Address (on Address lines) to Data Bus

Write: Store Data on Data Bus into word of Address (on Address lines)

m

n

ReadWrite

Addr

Data

Memory

COE 205

Concept of Address It is an index in the memory It represents a “geographic” location of a

word in the memory Number of Address lines and Word size

determine Memory Capacity (Size) Most of the time:

Memory size = 2n words = 2n * m bits

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RAM RAM: Random Access Memory Although the name is about the way memory is

accessed. Historically, volatile memory has been called RAM.

Volatile (do not retain information on power off) Used mainly as Central Memory for CPUs Two types of RAM

Static: Continuous Retention of Information Dynamic (DRAM): needs refresh cycle to maintain

information

ROM Non Volatile Used to store data (programs) that do not change

often (fixed) Many types

Mask ROM: Values set at fabrication stage. Values cannot be changed

Fuse PROM: Values set at burning phase. Values cannot be changed

EPROM: Can be erased (UV) EEPROM: Electrically erased Flash EEPROM: Easily reprogrammable. New: NVRAM (Non Volatile RAM): Fast access time.

Disk Drives

Hard Drive: suite of magnetic disks. Mechanically read and write data by moving a set of magnetic head over the disks

CD-ROM, DVD-ROM: Suite of optical disks read by measuring the time of laser reflexion between “1” and “0”

“1” “0”

N S

COE 205

Program Execution

A Program is a suite of instructions

Program Execution is Sequential

Program is stored in Memory

Program is executed by CPU

Instruction 1

Instruction 2

Instruction 3

Instruction n

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CPU

Executes Programs Stored in Memory Executes Instructions ONE by ONE Only “knows” instructions: Instruction Set DO NOT know any notion of Program as a

single entity. Everything is a suite of instructions

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CPU Structure (1)Is Mainly a Data Processing Unit Controlledby a Control Unit. Data Processing Unit: Datapath

Registers (Scratch pad working space or temporary data storage)

ALU: Arithmetic and Logic Unit Internal Buses

Control Unit: Generates Commands to “drive” Datapath operations

COE 205

CPU Structure (2)

Control Unit

Data Path is Similar to a Pipe Structure where valves are controlled by the Control Unit

Data

path A

LU

Reg

iste

r

Reg

iste

r

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Master Clock

Instructions Executed step by step Need a “Rhythm” Generator to move forward in the

steps:

TimeClock Cycle

Every CPU needs a Clock to control the transition from one execution step to the

next

Clock Frequency = 1/Clock Cycle Period : MHz

COE 205

Instruction Set Instruction Set is the Catalog of the CPU Defines what are ALL the possible

operations that the CPU can execute Only Instructions are recognized by CPU. CPU does NOT “understand” High Level

Language (text). CPU understands instructions coded in

numbers called machine code.

COE 205

Instruction parameters

Each Instruction specifies an action or a suite of actions: Action(s) “identifier” or Operation Code or Opcode Action arguments or operands Methods specifying how to access the operands,

called addressing modes

Instruction specified as:<Opcode> <Operand 1, addr_mode1> <Operand 2, addr_mode2> ….

COE 205

Number of Operands Many types of Instruction Sets Instruction Set with One Operand: Implicit

Register Called Accumulator. Everything goes to and from the accumulator:

Instruction Set with Two Operands: Many registers can be used as accumulators

Instruction Set with Three Operands: Mainly Register Based.

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Fetch – Decode - Execute

Fetch

Decode

Execute

CpuMemory

Address of next Instruction

InstructionRead Command

Opcode Reg Immediate

InstructionDecoder

Fetch

Decode

Execute

Address of Programs

Where the Address of next instruction is Stored ?

Need for an Instruction PointerCalled: “Program Counter” PC

• Critical Component of CPU• Conveniently useful for changing program

sequence (Branch instructions)

Instruction Register

Where is the current instruction going to be stored during its execution ?Need for a RegisterCalled: “Instruction Register”

• Critical Component of CPU• Internal Register. Cannot be used

(accessed) by instructions• Holds the current instruction until its

execution is completed• Tightly Coupled to the decoding

portion of the control unit• Connected to the datapath (to transfer

operand fields)

Opcode Op1 Op2

Instruction Decoder

Data Bus

Program in Memory

Binary code (machine code).

B8

00

05

MOV AX,5

03

C3ADD AX,BX

EB

E7JMP Next

Memory (8-bit)

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High Level Languages Machine independent. Cannot be run directly on the target machine Need to be translated to machine language Compiler: program that translates a HLL program to a machine language

program of a specific platform

The Machine language program produced by the compiler is the executable program.

Translating HLL programs to machine language programs is not a one-to-one mapping

A HLL statement translated to one or more machine language instructions

Usually, machine language programs produced by compilers are not efficient

Deals with Data types (integer, real, complex, user-defined) vs. machine language: no data types only binary words.

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Assembly Language Text version of machine language

Human friendly representation of machine language

Based on mnemonics (easy to memorize abbreviations of actions) instead of dealing with opcode numbers.

Complicated format simplified with some conventions

Text file translated into machine code by the Assembler

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Assembler

Program that assemble the programs written in assembly language into machine language

Because there is a ONE to ONE mapping between instructions written in assembly language and machine language instructions, the process is called: assembly rather than translation.

Disassembly (reverse process) is also easy because of the ONE to ONE relation between the assembly language instructions and the machine language instructions

MOV DX, 1

MOV AX, BX

MOV AX, CX

MOV AX, DX

ADD AX, 1

ADD AX, 2

ADD AX, BX

ADD AX, CX

ADD AX, i

SUB AX, 1

SUB AX, BX

ADD AX, 1234h

BA 0001

8B C3

8B C1

8B C2

83 C0 01

83 C0 02

03 C3

03 C1

03 06 0000

83 E8 01

2B C3

05 1234

Linker Program used to link together separately assembled/compiled

programs into a single executable code

Allows the programmers to develop different parts of a large program separately, test them separately and ‘freeze’ them for future use.

Allows the programmer to develop store portions of programs that have been intensively tested and used into a “program library” for anyone to re-use them.

Produces modular programs and greatly enables the management of large programming projects

Debugger/Monitor

These are tools that allow the assembly programmers to:

Display and alter the contents of memory and registers while running their code,

Perform disassembly of their machine code (show the assembly language equivalent),

Permit them to run their programs, stop (or halt) them, run them step-by-step or insert break points.

Break points: Positions in the program that if are encountered during run time, the program will be halted so the programmer can examine the memory and registers contents and determine what went wrong.

A User’s View of Computer Systems

Chapter 1: Page 38

What Is Assembly Language?

Some example assembly language instructions:inc resultmov class_size,45and mask1,128add marks,10

Some points to note: Assembly language instructions are cryptic Mnemonics are used for operations

inc for increment, mov for move (i.e., copy) Assembly language instructions are low level

Cannot write instructions such asmov marks, value

Chapter 1: Page 39

MIPS Examplesandi $t2,$t1,15addu $t3,$t1,$t2move $t2,$t1

What Is Assembly Language? (Cont’d)

Some simple high-level language instructions can be expressed by a single assembly instruction

Assembly Language C

inc result result++;

mov class_size,45 class_size = 45;

and mask1,128 mask1 &= 128;

add marks,10 marks += 10;

Chapter 1: Page 40

What Is Assembly Language? (Cont’d)

Most high-level language instructions need more than one assembly instruction

C Assembly Language

size = value; mov AX,value

mov size,AX

sum += x + y + z; mov AX,sum

add AX,x

add AX,y

add AX,z

mov sum,AX

Chapter 1: Page 41

What Is Assembly Language? (Cont’d)

Readability of assembly language instructions is much better than the machine language instructions

Machine language instructions are a sequence of 1s and 0s

Assembly Language Machine Language

(in Hex)

inc result FF060A00

mov class_size,45 C7060C002D00

and mask,128 80260E0080

add marks,10 83060F000A

Chapter 1: Page 42

What Is Assembly Language? (Cont’d)

MIPS examples

Assembly Language Machine Language

(in Hex)

nop 00000000

move $t2,$t15 000A2021

andi $t2,$t1,15 312A000F

addu $t3,$t1,$t2 012A5821

Chapter 1: Page 43

Why Program in Assembly Language?

Two main reasons: Efficiency

Space-efficiency Time-efficiency

Accessibility to system hardware Space-efficiency

Assembly code tends to be compact Time-efficiency

Assembly language programs tend to run faster Only a well-written assembly language program runs faster

Easy to write an assembly program that runs slower than its high-level language equivalent

Chapter 1: Page 44

Typical Applications Application that need one of the three advantages of the

assembly language Time-efficiency

Time-convenience Good to have but not required for functional correctness

Graphics Time-critical

Necessary to satisfy functionality Real-time applications

Aircraft navigational systems Process control systems Robot control software Missile control software

Chapter 1: Page 45

Performance: C versus Assembly Language

Chapter 1: Page 46

0

1

2

3

4

5

0 20 40 60 80 100

Number of calls (in millions)

Tim

e (s

econ

ds)

Last slide

C version

AL version