Architecture (I) Processor Architecture. – 2 – Processor Goal Understand basic computer organization Instruction set architecture Deeply explore the CPU

Architecture (I)

Processor ArchitectureProcessor ArchitectureProcessor ArchitectureProcessor Architecture

– 2 – Processor

GoalGoal

Understand basic computer organization Understand basic computer organization Instruction set architecture

Deeply explore the CPU working mechanismDeeply explore the CPU working mechanism How the instruction is executed: sequential and pipeline

version

Help you programmingHelp you programming Fully understand how computer is organized and works will

help you write more stable and efficient code.

– 3 – Processor

CPU Design (Why?)CPU Design (Why?)

It is interesting.It is interesting.

Aid in understanding how the overall computer system Aid in understanding how the overall computer system works.works.

Many design hardware systems containing processors.Many design hardware systems containing processors.

Maybe you will work on a processor design.Maybe you will work on a processor design.

– 4 – Processor

CPU DesignCPU Design

Instruction set architectureInstruction set architecture

Logic designLogic design

Sequential implementationSequential implementation

Pipelining and initial pipelined implementationPipelining and initial pipelined implementation

Making the pipeline workMaking the pipeline work

Modern processor designModern processor design

– 5 – Processor

Suggested ReadingSuggested Reading

- - Chap 4.1, 4.2Chap 4.1, 4.2

– 6 – Processor

Instruction Set Architecture #1Instruction Set Architecture #1

What is it ?What is it ? Assemble Language Abstraction Machine Language Abstraction

What does it provide?What does it provide? An abstraction of the real computer, hide the details of

implementationThe syntax of computer instructionsThe semantics of instructionsThe execution modelProgrammer-visible computer status

Instruction Set Architecture (ISA)

– 7 – Processor

Instruction Set Architecture #2Instruction Set Architecture #2Assembly Language ViewAssembly Language View

Processor stateRegisters, memory, …

Instructionsaddl, movl, leal, …How instructions are encoded as

bytes

Layer of AbstractionLayer of Abstraction Above: how to program machine

Processor executes instructions in a sequence

Below: what needs to be builtUse tricks to make it run fastE.g., execute multiple instructions

simultaneously

ISA

Compiler OS

CPUDesign

CircuitDesign

ChipLayout

ApplicationProgram

– 8 – Processor

Instruction Set Architecture #3Instruction Set Architecture #3

ISA define the processor familyISA define the processor family Two main kind: RISC and CISC

RISC:SPARC, MIPS, PowerPCCISC:X86 (or called IA32)

Another divide: Superscalar, VLIW and EPICSuperscalar: all the aboveVLIW: Philips TriMediaEPIC: IA64

Under same ISA, there are many different processorsUnder same ISA, there are many different processors From different manufacturers:

X86 from Intel and AMD and VIA

Different models8086, 80386, Pentium, Pentium 4

– 9 – Processor

%eax%ecx%edx%ebx

%esi%edi%esp%ebp

Y86 Processor StateY86 Processor State

Program RegistersSame 8 as with IA32. Each 32 bits

Condition CodesSingle-bit flags set by arithmetic or logical instructions

» OF: Overflow ZF: Zero SF:Negative

Program Counter Indicates address of instruction

MemoryByte-addressable storage arrayWords stored in little-endian byte order

Program registers Condition

codes

PC

Memory

OF ZF SF

P258 Figure 4.1P258 Figure 4.1P258 Figure 4.1P258 Figure 4.1

– 10 – Processor

Y86 InstructionsY86 Instructions

FormatFormat (P259) (P259) 1--6 bytes of information read from memory

Can determine instruction length from first byteNot as many instruction types, and simpler encoding than with

IA32

Each accesses and modifies some part(s) of the program state

Errata: JXX and call are 5 bytes long.Errata: JXX and call are 5 bytes long.



Encoding RegistersEncoding RegistersEach register has 4-bit IDEach register has 4-bit ID

Same encoding as in IA32, but IA32 using only 3-bit ID

Register ID 8 indicates “no register”Register ID 8 indicates “no register” Will use this in our hardware design in multiple places

%eax%ecx%edx%ebx

%esi%edi%esp%ebp

0123

6745



Instruction ExampleInstruction ExampleAddition InstructionAddition Instruction

Add value in register rA to that in register rBStore result in register rBNote that Y86 only allows addition to be applied to register data

Set condition codes based on result e.g., addl %eax,%esiEncoding: 60 06 Two-byte encoding

First indicates instruction typeSecond gives source and destination registers

addl rA, rB 6 0 rA rB

Encoded Representation

Generic Form



Arithmetic and Logical OperationsArithmetic and Logical Operations Refer to generically as

“OPl” Encodings differ only by

“function code”Low-order 4 bytes in first

instruction word

Set condition codes as side effect

Notice: no multiply or divide operation

addl rA, rB 6 0 rA rB

subl rA, rB 6 1 rA rB

andl rA, rB 6 2 rA rB

xorl rA, rB 6 3 rA rB

Add

Subtract (rA from rB)

And

Exclusive-Or

Instruction Code Function Code


Move OperationsMove Operations

Like the IA32 movl instruction Simpler format for memory addresses Give different names to keep them distinct

rrmovl rA, rB 2 0 rA rB Register --> Register

Immediate --> Registerirmovl V, rB 3 0 8 rB V

Register --> Memoryrmmovl rA, D(rB) 4 0 rA rB D

Memory --> Registermrmovl D(rB), rA 5 0 rA rB D


Distinct: Distinct: 清楚的清楚的Distinct: Distinct: 清楚的清楚的


Move Instruction ExamplesMove Instruction Examples

irmovl $0xabcd, %edx movl $0xabcd, %edx 30 82 cd ab 00 00

IA32 Y86 Encoding

rrmovl %esp, %ebx movl %esp, %ebx 20 43

mrmovl -12(%ebp),%ecxmovl -12(%ebp),%ecx 50 15 f4 ff ff ff

rmmovl %esi,0x41c(%esp)movl %esi,0x41c(%esp)

—movl $0xabcd, (%eax)

—movl %eax, 12(%eax,%edx)

—movl (%ebp,%eax,4),%ecx

40 64 1c 04 00 00


Jump InstructionsJump Instructions Refer to generically as “jXX” Encodings differ only by

“function code” Based on values of condition

codes Same as IA32 counterparts Encode full destination

addressUnlike PC-relative

addressing seen in IA32

jmp Dest 7 0

Jump Unconditionally

Dest

jle Dest 7 1

Jump When Less or Equal

Dest

jl Dest 7 2

Jump When Less

Dest

je Dest 7 3

Jump When Equal

Dest

jne Dest 7 4

Jump When Not Equal

Dest

jge Dest 7 5

Jump When Greater or Equal

Dest

jg Dest 7 6

Jump When Greater

Dest



Y86 Program StackY86 Program Stack Region of memory holding

program data Used in Y86 (and IA32) for

supporting procedure calls Stack top indicated by %esp

Address of top stack element

Stack grows toward lower addresses

Top element is at lowest address in the stack

When pushing, must first decrement stack pointer

When popping, increment stack pointer

%esp

•

•

•

IncreasingAddresses

Stack “Top”

Stack “Bottom”


Stack OperationsStack Operations

Decrement %esp by 4 Store word from rA to memory at %esp Like IA32

Read word from memory at %esp Save in rA Increment %esp by 4 Like IA32

pushl rA a 0 rA 8

popl rA b 0 rA 8



Subroutine Call and ReturnSubroutine Call and Return

Push address of next instruction onto stack Start executing instructions at Dest Like IA32

Pop value from stack Use as address for next instruction Like IA32

call Dest 8 0 Dest

ret 9 0



Miscellaneous InstructionsMiscellaneous Instructions

Don’t do anything

Stop executing instructions IA32 has comparable instruction, but can’t execute it in user mode We will use it to stop the simulator

nop 0 0

halt 1 0



Y86 Program StructureY86 Program Structure

Program starts at address 0

Must set up stackMake sure don’t

overwrite code!

Must initialize data Can use symbolic

names

irmovl Stack,%esp # Set up stackrrmovl %esp,%ebp # Set up frameirmovl List,%edxpushl %edx # Push argumentcall len2 # Call Functionhalt # Halt

.align 4List: # List of elements

.long 5043

.long 6125

.long 7395

.long 0

# Functionlen2:

. . .

# Allocate space for stack.pos 0x100Stack:


Assembling Y86 ProgramAssembling Y86 Program

Generates “object code” file eg.yoActually looks like disassembler output

unix> yas eg.ys

0x000: 308400010000 | irmovl Stack,%esp # Set up stack 0x006: 2045 | rrmovl %esp,%ebp # Set up frame 0x008: 308218000000 | irmovl List,%edx 0x00e: a028 | pushl %edx # Push argument 0x010: 8028000000 | call len2 # Call Function 0x015: 10 | halt # Halt 0x018: | .align 4 0x018: | List: # List of elements 0x018: b3130000 | .long 5043 0x01c: ed170000 | .long 6125 0x020: e31c0000 | .long 7395 0x024: 00000000 | .long 0


Simulating Y86 ProgramSimulating Y86 Program

Instruction set simulatorComputes effect of each instruction on processor statePrints changes in state from original

unix> yis eg.yo

Stopped in 41 steps at PC = 0x16. Exception 'HLT', CC Z=1 S=0 O=0Changes to registers:%eax: 0x00000000 0x00000003%ecx: 0x00000000 0x00000003%edx: 0x00000000 0x00000028%esp: 0x00000000 0x000000fc%ebp: 0x00000000 0x00000100%esi: 0x00000000 0x00000004

Changes to memory:0x00f4: 0x00000000 0x000001000x00f8: 0x00000000 0x000000150x00fc: 0x00000000 0x00000018


SummarySummary

Y86 Instruction Set ArchitectureY86 Instruction Set Architecture Similar state and instructions as IA32 Simpler encodings Somewhere between CISC and RISC

How Important is ISA Design?How Important is ISA Design? Less now than before

With enough hardware, can make almost anything go fast

Intel is moving away from IA32Does not allow enough parallel execution Introduced IA64

» 64-bit word sizes (overcome address space limitations)» Radically different style of instruction set with explicit parallelism» Requires sophisticated compilers

Radically:Radically: 根本上根本上Radically:Radically: 根本上根本上


Logic DesignLogic Design

Digital circuitDigital circuit What is digital circuit? Know what a CPU will base on?

Hardware Control Language (HCL)Hardware Control Language (HCL) A simple and functional language to describe our CPU

implementation Syntax like C


Category of CircuitCategory of Circuit

Analog CircuitAnalog Circuit Use all the range of Signal Most part is amplifier Hard to model and automatic design Use transistor and capacitance as basis We will not discuss it here

Digital CircuitDigital Circuit Has only two values, 0 and 1 Easy to model and design Use true table and other tools to analyze Use gate as the basis The voltage of 1 is differ in different kind circuit.

E.g. TTL circuit using 5 voltage as 1

Amplifier: Amplifier: 放大器放大器TransistorTransistor ：：晶体管晶体管Capacitance: Capacitance: 电容电容

Amplifier: Amplifier: 放大器放大器TransistorTransistor ：：晶体管晶体管Capacitance: Capacitance: 电容电容


Digital SignalsDigital Signals

Use voltage thresholds to extract discrete values from continuous signal

Simplest version: 1-bit signalEither high range (1) or low range (0)With guard range between them

Not strongly affected by noise or low quality circuit elementsCan make circuits simple, small, and fast

Voltage

Time

0 1 0


Overview of Logic DesignOverview of Logic Design

Fundamental Hardware RequirementsFundamental Hardware Requirements Communication

How to get values from one place to another Computation Storage (Memory) Clock Signal

Bits are Our FriendsBits are Our Friends Everything expressed in terms of values 0 and 1 Communication

Low or high voltage on wire Computation

Compute Boolean functions Storage Clock Signal


Category of Digital CircuitCategory of Digital Circuit

Combinational CircuitCombinational Circuit Without memory. So the circuit can’t have state. Any same

input will get the same output at any time. Needn’t clock signal Typical application: ALU

Sequential CircuitSequential Circuit = Combinational circuit + memory and clock signal Have state. Two same inputs may not generate the same

output. Use clock signal to control the run of circuit. Typical application: CPU


Computing with Logic Gates P272 Figure 4.8Computing with Logic Gates P272 Figure 4.8

Outputs are Boolean functions of inputs Not an assignment operation, just give the circuit a name Respond continuously to changes in inputs

With some, small delay

ab out

ab out a out

out = a && b out = a || b out = !a

And Or Not

Voltage

Time

a

ba && b

Rising Delay Falling Delay


Combinational CircuitsCombinational Circuits

Acyclic Network of Logic GatesAcyclic Network of Logic Gates Continuously responds to changes on inputs Outputs become (after some delay) Boolean functions of

inputs

Acyclic Network

Inputs Outputs


Bit Equality P272 Figure 4.9Bit Equality P272 Figure 4.9

Generate 1 if a and b are equal

Hardware Control Language (HCL)Hardware Control Language (HCL) Very simple hardware description language

Boolean operations have syntax similar to C logical operations

We’ll use it to describe control logic for processors

Bit equala

b

eqbool eq = (a&&b)||(!a&&!b)

HCL Expression


Bit-Level Multiplexor P273 Figure 4.10Bit-Level Multiplexor P273 Figure 4.10

Control signal s Data signals a and b Output a when s=1, b when s=0 Its name: MUX Usage: Select one signal from a couple of signals

Bit MUX

b

s

a

out

bool out = (s&&a)||(!s&&b)

HCL Expression


Word Equality P274 Figure 4.11Word Equality P274 Figure 4.11

32-bit word size HCL representation

Equality operationGenerates Boolean value

b31Bit equal

a31

eq31

b30Bit equal

a30

eq30

b1Bit equal

a1

eq1

b0Bit equal

a0

eq0

Eq

==B

A

Eq

Word-Level Representation

bool Eq = (A == B)

HCL Representation


Word Multiplexor P275 Figure 4.12Word Multiplexor P275 Figure 4.12

Select input word A or B depending on control signal s

HCL representationCase expressionSeries of test : value pairsOutput value for first successful test

Word-Level Representation

HCL Representation

b31

s

a31

out31

b30

a30

out30

b0

a0

out0

int Out = [ s : A; 1 : B;];

s

B

AOutMUX


HCL Word-Level Examples P277, P266HCL Word-Level Examples P277, P266

Find minimum of three input words

HCL case expression Final case guarantees

match

AMin3MIN3B

Cint Min3 = [ A < B && A < C : A; B < A && B < C : B; 1 : C;];

D0

D3

Out4

s0s1

MUX4D2D1

Select one of 4 inputs based on two control bits

HCL case expression Simplify tests by

assuming sequential matching

int Out4 = [ !s1&&!s0: D0; !s1 : D1; !s0 : D2; 1 : D3;];

Minimum of 3 Words

4-Way Multiplexor


OFZFSF

OFZFSF

OFZFSF

OFZFSF

Arithmetic Logic Unit P278 Figure 4.13Arithmetic Logic Unit P278 Figure 4.13

Combinational logicContinuously responding to inputs

Control signal selects function computedCorresponding to 4 arithmetic/logical operations in Y86

Also computes values for condition codes We will use it as a basic component for our CPU

ALU

Y

X

X + Y

0

ALU

Y

X

X - Y

1

ALU

Y

X

X & Y

2

ALU

Y

X

X ^ Y

3

A

B

A

B

A

B

A

B

Jiang Weihua


StorageStorage

RegistersRegisters Hold single words or bits Loaded as clock rises Not only program registers

Random-access memoriesRandom-access memories Hold multiple words E.g. register file, memory Possible multiple read or write ports Read word when address input changes Write word as clock rises

I O

Clock


Register Operation P279 Figure 4.14Register Operation P279 Figure 4.14

Stores data bits For most of time acts as barrier between input and output As clock rises, loads input

State = x

RisingclockOutput = xInput = y

x

State = y

Output = y

y

Barrier: Barrier: 屏障屏障Barrier: Barrier: 屏障屏障


State Machine ExampleState Machine Example

Accumulator circuit

Load or accumulate on each cycle

Comb. Logic

ALU

0

OutMUX

0

1

Clock

In

Load

x0 x1 x2 x3 x4 x5

x0 x0+x1 x0+x1+x2 x3 x3+x4 x3+x4+x5

Clock

Load

In

Out


Random-Access Memory P280Random-Access Memory P280

Stores multiple words of memoryAddress input specifies which word to read or write

Register fileHolds values of program registers %eax, %esp, etc.Register identifier serves as address

» ID 8 implies no read or write performed

Multiple PortsCan read and/or write multiple words in one cycle

» Each has separate address and data input/output

Registerfile

Registerfile

A

B

W dstW

srcA

valA

srcB

valB

valW

Read ports Write port

Clock


Register File TimingRegister File TimingReadingReading

Like combinational logic Output data generated based on input

address After some delay

WritingWriting Like register Update only as clock rises

Registerfile

Registerfile

A

B

srcA

valA

srcB

valB

y2

Registerfile

Registerfile

W dstW

valW

Clock

x2

Risingclock Register

fileRegister

fileW dstW

valW

Clock

y2

x2

x

2


Hardware Control LanguageHardware Control Language Very simple hardware description language Can only express limited aspects of hardware operation

Parts we want to explore and modify

Data TypesData Types bool: Boolean

a, b, c, …

int: wordsA, B, C, …Does not specify word size---bytes, 32-bit words, …

StatementsStatements bool a = bool-expr ; int A = int-expr ;


HCL OperationsHCL Operations Classify by type of value returned

Boolean ExpressionsBoolean Expressions Logic Operations

a && b, a || b, !a Word Comparisons

A == B, A != B, A < B, A <= B, A >= B, A > B Set Membership

A in { B, C, D }» Same as A == B || A == C || A == D

Word ExpressionsWord Expressions Case expressions

[ a : A; b : B; c : C ]Evaluate test expressions a, b, c, … in sequenceReturn word expression A, B, C, … for first successful test


SummarySummary

ComputationComputation Performed by combinational logic Computes Boolean functions Continuously reacts to input changes

StorageStorage Registers

Hold single wordsLoaded as clock rises

Random-access memoriesHold multiple wordsPossible multiple read or write portsRead word when address input changesWrite word as clock rises

Documents

Architecture (I) Processor Architecture. – 2 – Processor Goal Understand basic computer organization Instruction set architecture Deeply explore the CPU