name all the 4 parts of the fetch execute · instruction format operation code, a.k.a. opcode...

QUIZ

Name all the 4 parts of the “fetch-execute” cycle.

1

Solution

Name all the 4 parts of the “fetch-execute” cycle.

2

Name two fundamental differences between magnetic drives and optical drives:

•

•

3

QUIZ

Define Embedded Systems

4

QUIZ

5

QUIZ

What are two ways to create a non-vNarchitecture?

What are the 3 parallel architectures we covered?

What are two ways to create a non-vNarchitecture? A: By using more than one MM, or by using more than one CPU.

What are the 3 parallel architectures we covered?

6

Solution

Pipelined CPUs

Synchronous CPUs

Parallel (non-synchronous)

CPUs

QUIZ Pipelining

A computer pipeline has 4 processors, as shown above. Each processor takes 15 ms to execute, and each instruction must go sequentially through all 4 processors.

A program has 10 instructions. Calculate how long it takes to run it:

• without pipelining

• with pipelining

7

8

Extra-credit QUIZ

Low-level software

Components

Circuits

Gates

Transistors

Abstractions and more abstractions …

10You are here

6.1 Computer Operations

Computer = programmable electronic device that can store, retrieve, and process data

Von Neumann architecture:

• Data and instructions to manipulate the data are represented in the same way (binary) and are stored in the same place (memory)

• For processing, both data and

instructions have to be brought

into the CPU (fetch-execute cycle)

11

6.2 Machine Language

Machine language = The language made up of binary coded instructions built into the hardware of a particular computer and used directly by the computer

Why would anyone use machine language?

(Hint: they had no choice. Why?)

12Image source: http://www.alpcentauri.info/chapter_18.html

Remember: The Fetch-Execute Cycle

13

According to the CPU’s

machine language

Characteristics of machine language:

– Every processor type has its own set of specific machine instructions

– The relationship between the processor and the instructions it can carry out is completely integrated

– Each machine-language instruction does only one very low-level task

14

Pep/8 Virtual Computer

Virtual computer

A hypothetical machine designed to contain the important features of a real machine

Pep/8

A virtual computer designed by Stanley Warford that has 39 machine-language instructions

(We’re going to cover only a few of them!)

15

Extra-credit

16

Pep/8 Registers

– The program counter (PC) (contains the address of the next instruction to be executed)

– The instruction register (IR) (contains a copy of the instruction being executed)

– The accumulator (register A)

The memory unit is made up of 65,636 Bytes of storage

17

Can you figure out how long the Pep/8 address is?

QUIZ

The previous version of Pep, Pep/7, could use only 12 bits for memory addresses.

How many memory cells could Pep/7 address?

18

19

Explain the

address format!

16 bits

24

bits

20

Explain the

address format!

Can you show what

instructions look like

in memory?

Instruction Format

21

Instruction Format

Operation code, a.k.a. opcodeSpecifies which instruction is to be carried outRegister specifierSpecifies which register is to be used (only use A in

this chapter)Addressing-mode specifierSays how to interpret the operand part of the

instruction:• Direct• Immediate

22

Say that again?!?

Instruction Format

Addressing-mode specifierSays how to interpret the operand part of the

instruction:• Direct• Immediate

2 + 3 ImmediateA + B Direct

23

??

24

Immediate and direct addressing modes

Immediate and direct addressing modes

25

Example:

ADD 42 to accumulator A

What exactly am I to add?

Instruction Format

26

Addressing modes:

• immediate

• direct

Is there something we are not telling you

about Pep’s addressing modes?

PEP/8 machine instructions

27

28

What does this instruction mean, what is

its hex code, and what exactly does it do?

EOL 1

QUIZ

• Name all the 4 parts of the “fetch-execute” cycle.

• What do IR, A, and PC stand for in the computer’s architecture?

• Name and explain the 2 addressing modes we’ve covered.

29

QUIZ: Immediate vs. direct addressing

30

We have this Pep instruction:

SUB 30 from accumulator A

What exactly will Pep subtract?

31

Solution

A: It depends on the addressing

mode!

• If immediate (000), then the

integer 30 goes in A.

• If direct (001), then the

content of the memory

address 30 goes in A.


SUB 30 from accumulator A

What exactly will Pep subtract?

32


LOAD 20 (decimal) into

accumulator A

What exactly will Pep load?

QUIZ: Immediate vs. direct addressing

33



34



35

What do these instructions mean, what are

their hex codes, and what exactly do they do?

Wait a second ...

36

ConclusionsIt is useless to write operands into IR.

IR is written only in the FETCH stage of the Fetch-Execute cycle, when the 3 bytes of the instruction are brought from memory.

Operands can be written only to:

• Accumulator

• Memory

Some instructions cannot have the immediate addressing mode

37

38



Why is there only one on this page?



40



Problem 17 / 190

41

The PEP/8 memory has the following contents:

0001 A2

0002 11

0003 00

0004 FF

What are the contents of reg. A after this instruction

is executed:

C1 00 02

The first step is …

Problem 17 / 190

42


0001 A2

0002 11

0003 00

0004 FF


is executed:

C1 00 02

1100 0001 0000 0000 0000 0010

Problem 16 / 189

43


0001 A2

0002 11

0003 00

0004 FF


is executed:

C1 00 01

44

0001 A2

0002 11

0003 00

0004 FF

Instruction

executed:

C1 00 01

6.3 Program to write "Hello"

45

Every program ends with this!

Your turn!

What does this program do?

1111

0000

1111

1 0000

47

Steps for executing a machine-language

program

Loader

Program

in

memoryExecute

Machine

code

program

in a file

on disk

SKIP Pep/8 Simulator

48EOL 2

Problem 33 / 191

49

The PEP/8 memory has the following program in

memory (in hex):

0001 49

0002 00

0003 08

0004 51

0005 00

0006 08

0007 00

Convert the program to binary and

explain in your own words what it does.

Fact: Writing programs in machine language sucks!

(i.e. it is time-consuming, boring, error-prone, unintuitive, etc.)

50

… that’s why we invented

assembly language

51

6.4 Assembly Language

Assembly language

A language that uses mnemonic codes to represent machine-language instructions

AssemblerA program that reads each of the instructions in mnemonic form and translates it into the machine-language equivalent

52

53

Steps for executing anassembly-language program

Loader

Program

in

memoryExecute

Pep/8 Assembly Language

54

Opcodeis 31

Opcodeis 38

Opcodeis 39

Opcodeis 04

“Hello” program in assembly

CHARO 0x0048, i ;Outputs character 'H'

CHARO 0x0065, i

CHARO 0x006C, i

CHARO 0x006C, i

CHARO 0x006F, i

STOP

.END

55

mnemonic operand addressing

modecomments

What in the

world is this?!

A New Program

56

Problem: Read and sum three

values and print the sum

How would you do it by hand?

Declaring variables in assembly:We simply reserve space in memory for them!

57

Labels – they are just

placeholders for

memory addresses

Assembler directives, a.k.a. pseudo-ops

58

What is the difference between

operations and pseudo operations?

Completed Program

59

sum: .WORD 0x0000

num1: .BLOCK 2

num2: .BLOCK 2

num3: .BLOCK 2

main: LDA sum,d

DECI num1,d

ADDA num1,d

DECI num2,d

ADDA num2,d

DECI num3,d

ADDA num3,d

STA sum,d

DECO sum,d

STOP

.END

Completed Program

60

sum: .WORD 0x0000

num1: .BLOCK 2

num2: .BLOCK 2

Num3: .BLOCK 2

main: LDA sum,d

DECI num1,d

ADDA num1,d

DECI num2,d

ADDA num2,d

DECI num3,d

ADDA num3,d

STA sum,d

DECO sum,d

STOP

.END

Houston, we have a problem!

How does the CPU know that the program starts here?

Solution: “Branch” instruction

61

BR main

sum: .WORD 0x0000

num1: .BLOCK 2

num2: .BLOCK 2

num3: .BLOCK 2

main: LDA sum,d

DECI num1,d

ADDA num1,d

DECI num2,d

ADDA num2,d

DECI num3,d

ADDA num3,d

STA sum,d

DECO sum,d

STOP

.END

See comments on next slide

62

Completed ProgramUnconditional

branch!

63

Your turn! Change the program so it adds only two numbers: always 7 + 42

EOL 3

We have covered the beginning of section 6.4. We stopped before the sub-section A Program with Branching.

• Read the text carefully and make sure you can explain in your own words what each instruction accomplishes.

• Individual work (do in notebook for next time):

16, 17, 19, 21-26

64

EOL 3

Decision-making instructions

65

BR Set PC to operand unconditionally

BRLTi Set PC to operand if A < 0

BREQi Set PC to operand if A = 0

Decision making problem: Same as previous “sum” program, but print the sum only if positive or zero; if negative, print an error message

66

negMsg: CHARO 0x0045,i

BR finish

main: LDA sum,d

…

BRLT negMsg

STA sum,d

DECO sum,d

finish: STOP

What ASCII code is this?

Decision making problem: Same as before, but print the sum only if positive or zero; if negative, print ‘E’ (Error)


BR finish

main: LDA sum,d

…

BRLT negMsg

STA sum,d

DECO sum,d

finish: STOP

How many ways are there to reach finish?

ASCII code for 'E'

QUIZ: Would the decision program from the first example still work if the negMsg block were placed after the main program instead of before?

68

main: LDA sum,d

…

BRLT negMsg

STA sum,d

DECO sum,d

finish: STOP


BR finish

QUIZ: What does this program do?

69

BR main

a: .BLOCK 2

main: DECI a, d

LDA a, d

SUBA 0x002A, i

STA a, d

DECO a, d

STOP

.END

A: It subtracts 42 from the number entered, and displays the result.

70

BR main

a: .BLOCK 2

main: DECI a, d

LDA a, d

SUBA 0x002A, i

STA a, d

DECO a, d

STOP

.END

Solution

QUIZ: What does this program do?

71

BR main

a: .BLOCK 2

main: DECI a, d

LDA a, d

SUBA 0x002A, i

STA a, d

BREQ yes

DECO a, d

fin: STOP

yes: CHARO 0x0046, i

BR fin

.END

ASCII code for 'F'

QUIZ: Write an assembly program to subtract 2010 from 4210 and put the result in memory

72

BR main

sum: .WORD 0x0000

num1: .BLOCK 2

num2: .BLOCK 2

num3: .BLOCK 2

main: LDA sum,d

DECI num1,d

ADDA num1,d

DECI num2,d

ADDA num2,d

DECI num3,d

ADDA num3,d

STA sum,d

DECO sum,d

STOP

.END

Take inspiration from the

program we studied last time:

Three quizzes for individual work

Write a program that adds the number 3 to a number entered by the user, and prints :

• the result if equal to zero, otherwise it prints nothing.

• the result if less than zero, otherwise it prints nothing.

• the result if greater than zero, otherwise it prints nothing.

73

74

What does this program do? (p.173)

CPA must

always be

followed by a

conditional

branch!

High-level software (Ch.9)

Algorithms (and data structures)

Low-level software

Components

Circuits

Gates

Transistors

6.5 Algorithms and Pseudocode

Algorithm = A sequence of steps for solving a problem

Muḥammad ibn Mūsā al-Khwārizmī (780-850A.D.)

76

Remember: Decision-making instructions

77

BR Set PC to operand unconditionally

BRLTi Set PC to operand if A < 0

BREQi Set PC to operand if A = 0

How to describe an algorithm in an intuitive way?

78

Flowcharts!

Not in text

We use decision-making instructions to build:

• branches

• loops

Problems with flowcharts:• They’re hard to follow when they get complex

79

Not in text


• They’re hard to draw in electronic documents

80

Not in text


• They’re hard to draw in electronic documents

81

Not in text

Our text uses only pseudocode

6.5 Algorithms and Pseudocode

Pseudocode = A mixture of English and formatting to make the steps in an algorithm explicit

There are no syntax rules in pseudocode!

Pseudocode is not case sensitive!

Example: Repeated-division algorithm (convert base-10 number to other bases):

82

While ( the quotient is not zero )

Divide the decimal number by the new base

Make the remainder the next digit to the left in the answer

Replace the original decimal number with the quotient

Algorithms can also be described in natural language!

83

… but pseudocode is more precise

84

IF concerned about cholesterol

Put butter substitute in a pot

ELSE

Put butter in a pot

Turn on burner

Put pot on the burner

WHILE (NOT bubbling)

Leave pot on the burner

Put other ingredients in the blender

Turn on blender

WHILE (more in pot)

Pour contents into lender in slow steam

Turn off blender

Draw the flowchart for this pseudocode

85

IF concerned about cholesterol

Put butter substitute in a pot

ELSE

Put butter in a pot

Turn on burner

Put pot on the burner

WHILE (NOT bubbling)

Leave pot on the burner

Put other ingredients in the blender

Turn on blender

WHILE (more in pot)

Pour contents into lender in slow steam

Turn off blender

Pseudocode functionality

Pseudocode has all of the concepts encountered in any high-level programming language, only the syntax is informal:

– Variables

– Assignment

– I/O

– Selection / decision

– Repetition / loop

– Boolean expressions

86

Reading assignment:

Pages 175-179 of the text

Refer to your Python programming experience!

87

We can test a pseudocode algorithm w/pencil & paper, a.k.a. “desk checking”

88

What is 93 in base 8?

93/8 gives 11 remainder 5

11/8 gives 1 remainder 3

1/ 8 gives 0 remainder 1

answer 1 3 5

While ( the quotient is not zero )

Divide the decimal number by the new base

Make the remainder the next digit to the left in the answer

Replace the original decimal number with

89

Organizing the solution in a computer-like way gives us

better idea of what is required for the computer to

execute it, e.g. two numbers need to be entered, etc.

90

QUIZ: Desk-check the repeated division algorithm

with decimalNumber = 242, and newBase = 8

Answer: 362

SKIP 6.6 Testing

91

Read and take notes in notebook:

Software Piracy and Copyrighting

Have you every "borrowed" software

from a friend?

Have you ever "lent" software to a

friend?

Did you know that about 100,000 jobs are

lost in the US every year due to such

"borrowing" and "lending?"

92

Chapter Review Questions

• List the operations that a computer can perform

• Describe the important features of the Pep/8 virtual machine

• Distinguish between immediate addressingmode and direct addressing mode

• Write a simple machine-language program

• Distinguish between machine language and assembly language

93


• Describe the steps in creating and running an assembly-language program

• Write a simple program in assembly program

• Distinguish between instructions to the assembler (a.k.a. directives) and instructions to be translated into machine code (a.k.a. executable instructions)

• Distinguish between following an algorithm and developing one

94


• Describe the pseudocode constructs used in expressing an algorithm

• Use pseudocode to express and algorithm

• Distinguish between black-box and clear-box testing

95

HomeworkDue Wednesday, Oct.26

End of chapter exercises:

• 10, 11, 12, 13, 14, 15, 18, 20,– Correction in 20: use E1 instead of E0

• 27, 34,– Hint for 34: machine code 31 means decimal input

• 36, 41,– Hint for 41: How are integers represented in Pep/8?

• 44, 45

All PEP instructions, with machine codes00 Stop STOP

04 Branch unconditional BR

08 Branch if Less Than BRLT

0A Branch if equal BREQ

31 Decimal Input Direct DECI

38 Decimal Output Immediate DECO

39 Decimal Output Direct DECO

49 Char. Input Direct CHARI

50 Char. Output Immediate CHARO

51 Char. Output Direct CHARO

70 Add to A Immediate ADDA

71 Add to A Direct ADDA

80 Subtract from A Immediate SUBA

81 Subtract from A Direct SUBA

C0 Load into A Immediate LDA

C1 Load into A Direct LDA

E1 Store A Direct STA 97

name all the 4 parts of the fetch execute · instruction format operation code, a.k.a. opcode...

Documents