Name all the 4 parts of the “fetch-execute” cycle. · Operation code, a.k.a. opcode. ......

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

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Solution

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

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Name two fundamental differences between magnetic drives and optical drives:••

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QUIZ

Name two fundamental differences between magnetic drives and optical drives:• Data is stored using magnetic properties vs.

optical properties.• In a HDD, the speed of rotation is constant,

but in an optical drive rotation is faster on the inner tracks, resulting in Constant Linear Velocity (CLV)

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Solution

Define Embedded Systems

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QUIZ

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QUIZWhat are two ways to create a non-vN architecture?What are the 3 parallel architectures we covered?

What are two ways to create a non-vN architecture? A: By using more than one MM, or by using more than one CPU.What are the 3 parallel architectures we covered?

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Solution

Pipelined CPUs

Synchronous CPUs

Parallel (non-synchronous) CPUs

QUIZ Pipelining

A computer pipeline has 4 processors, as shown above. Each processor takes 15 µs 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

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Extra-credit QUIZ

Low-level softwareComponents

Circuits

Gates

Transistors

√

√

√

√

Abstractions and more abstractions …

11You are here

6.1 Computer OperationsComputer = programmable electronic device

that can store, retrieve, and process dataVon 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)

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6.2 Machine LanguageMachine 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?)

13Image source: http://www.alpcentauri.info/chapter_18.html

Remember: The Fetch-Execute Cycle

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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

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Pep/8 Virtual Computer

Virtual computerA hypothetical machine designed to contain the

important features of a real machine

Pep/8A virtual computer designed by Stanley Warford

that has 39 machine-language instructions(We’re going to cover only a few of them!)

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Extra-credit

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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

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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?

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20

Explain the address format!

16 bits

24bits

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Explain the address format!

Can you show whatinstructions look like

in memory?

Instruction Format

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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

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Say that again?!?

Instruction Format

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

instruction:• Direct• Immediate

2 + 3 ImmediateA + B Direct

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??

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Immediate and direct addressing modes

QUIZ: Immediate vs. direct addressing

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We have this Pep instruction:

SUB 30 from accumulator A

What exactly will Pep subtract?

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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?

PEP/8 machine instructions

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What does this instruction mean, what isits 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.

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31


LOAD 20 (decimal) into accumulator A

What exactly will Pep load?

QUIZ: Immediate vs. direct addressing

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33


34

What do these instructions mean, what aretheir hex codes, and what exactly do they do?

Wait a second ...

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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• MemorySome instructions cannot have the immediate addressing mode

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Why is there only one on this page?


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Problem 17 / 190

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The PEP/8 memory has the following contents:0001 A20002 110003 000004 FF

What are the contents of reg. A after this instructionis executed:

C1 00 02

The first step is …

Problem 17 / 190

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C1 00 02

1100 0001 0000 0000 0000 0010

Problem 16 / 189

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C1 00 01

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0001 A20002 110003 000004 FF

Instructionexecuted:

C1 00 01

6.3 Program to write "Hello"

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Every program ends with this!

Your turn!What does this program do?

1111

0000

1111

1 0000

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Steps for executing a machine-language

program

Loader

Program in

memoryExecute

Machine code

program in a file on disk

SKIP Pep/8 Simulator

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Fact: Writing programs in machine language sucks!

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

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… that’s why we invented assembly language

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6.4 Assembly Language

Assembly languageA 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

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Steps for executing anassembly-language program

Loader

Program in

memoryExecute

Pep/8 Assembly Language

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Opcode is 31

Opcode is 38

Opcode is 39

Opcode is 04

“Hello” program in assembly

CHARO 0x0048, i ;Outputs character 'H'CHARO 0x0065, iCHARO 0x006C, iCHARO 0x006C, iCHARO 0x006F, i STOP.END

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mnemonic operand addressing mode

comments

What in the world is this?!

A New Program

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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!

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Labels – they are just placeholders for memory addresses

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

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What is the difference between operations and pseudo operations?

Completed Program

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sum: .WORD 0x0000num1: .BLOCK 2num2: .BLOCK 2num3: .BLOCK 2main: LDA sum,d

DECI num1,d ADDA num1,d DECI num2,d ADDA num2,d DECI num3,d ADDA num3,d STA sum,dDECO sum,dSTOP .END

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.

• Quick work (do in notebook for next time):16, 17, 19, 21-26

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EoHW 2

Problem 33 / 191

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The PEP/8 memory has the following program in memory (in hex):

0001 490002 000003 080004 510005 000006 080007 00

Convert the program to binary andexplain in your own words what it does.

Completed Program

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sum: .WORD 0x0000num1: .BLOCK 2num2: .BLOCK 2Num3: .BLOCK 2main: LDA sum,d


Houston, we have a problem!

How does the CPU know that the program starts here?

Solution: “Branch” instruction

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BR main sum: .WORD 0x0000num1: .BLOCK 2num2: .BLOCK 2num3: .BLOCK 2main: 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

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Completed ProgramUnconditional branch!

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

Decision-making instructions

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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

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negMsg: CHARO 0x0045,i BR finish

main: LDA sum,d…BRLT negMsgSTA sum,dDECO sum,d

finish: STOP

What ASCII code is this?

Read and add the

numbers, as before

Decision making problem: Same as before, but print the sum only if positive or zero; if negative, print ‘E’ (Error)negMsg: CHARO 0x0045,i

BR finishmain: LDA sum,d

…BRLT negMsgSTA sum,dDECO sum,d

finish: STOP

How many ways are there to reach finish?

ASCII code for 'E'

QUIZ: What does this program do?

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BR maina: .BLOCK 2main: DECI a, d

LDA a, dSUBA 0x002A, iSTA a, dDECO a, dSTOP.END

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

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BR maina: .BLOCK 2main: DECI a, d

LDA a, dSUBA 0x002A, iSTA a, dDECO a, dSTOP.END

Solution

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

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BR main sum: .WORD 0x0000num1: .BLOCK 2num2: .BLOCK 2num3: .BLOCK 2main: LDA sum,d


Take inspiration from this previous

program:

Three problems for more studyWrite a PEP assembly 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.

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A Program with a Loop (p.174-5)

CPA must always be followed by a conditional branch!

High-level software (Ch.9)

Algorithms (and data structures)

Low-level softwareComponents

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.)

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Remember: Decision-making instructions

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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?

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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

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Not in text

Problems with flowcharts:• They’re hard to follow when they get complex• They’re hard to draw in electronic documents

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Not in text

Problems with flowcharts:• They’re hard to follow when they get complex• They’re hard to draw in electronic documents

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Not in text

Our text uses only pseudocode

6.5 Algorithms and PseudocodePseudocode = A mixture of English and

formatting rules 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):

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While ( the quotient is not zero )Divide the decimal number by the new baseMake the remainder the next digit to the left in the answerReplace the original decimal number with the quotient

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

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

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What is 93 in base 8?93/8 gives 11 remainder 511/8 gives 1 remainder 31/ 8 gives 0 remainder 1

answer 1 3 5

While ( the quotient is not zero )Divide the decimal number by the new baseMake the remainder the next digit to the left in the answerReplace the original decimal number with

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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.

SKIP 6.6 Testing

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Read and take notes in notebook:Bio: Konrad ZuseEthics: Software Piracy and Copyrighting

Have you every "borrowed" softwarefrom a friend?

Have you ever "lent" software to a friend?

Did you know that about 100,000 jobs arelost in the US every year due to such"borrowing" and "lending?"

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Homework - Due Thursday, Nov.1

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, DECI

• 41 - Hint: On how many bits are integers represented in Pep/8?

• 44, 45– Hint for 45: Very similar to the text program!

All PEP instructions, with machine codes00 Stop STOP 04 Branch unconditional BR08 Branch if Less Than BRLT0A Branch if equal BREQ31 Decimal Input Direct DECI38 Decimal Output Immediate DECO39 Decimal Output Direct DECO49 Char. Input Direct CHARI 50 Char. Output Immediate CHARO51 Char. Output Direct CHARO70 Add to A Immediate ADDA71 Add to A Direct ADDA80 Subtract from A Immediate SUBA 81 Subtract from A Direct SUBAC0 Load into A Immediate LDAC1 Load into A Direct LDAE1 Store A Direct STA

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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

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• 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

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• Describe the pseudocode constructs used in expressing an algorithm

• Use pseudocode to express and algorithm• Distinguish between black-box and clear-box

testing

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Name all the 4 parts of the “fetch-execute” cycle. · Operation code, a.k.a. opcode. ......

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