cs61c l27 single cycle cpu control ii (1) garcia © ucb lecturer psoe dan garcia ddgarcia...

CS61C L27 Single Cycle CPU Control II (1) Garcia © UCB

Lecturer PSOE Dan Garcia

www.cs.berkeley.edu/~ddgarcia

inst.eecs.berkeley.edu/~cs61c CS61C : Machine Structures

Lecture 28 – Single Cycle CPU Control II

DARPA $s drying up…ouch!

www.nytimes.com/2005/04/02/technology/02darpa.html?

“I'm worried and depressed,” – David Patterson, president of the ACM.

There is a significant shift of $ from “Blue Sky” research to military contractors. This is a

significant shift, mostly for the worse.


°5 steps to design a processor• 1. Analyze instruction set => datapath requirements• 2. Select set of datapath components & establish clock

methodology• 3. Assemble datapath meeting the requirements• 4. Analyze implementation of each instruction to

determine setting of control points that effects the register transfer.• 5. Assemble the control logic

°Control is the hard part°MIPS makes that easier• Instructions same size• Source registers always in same place• Immediates same size, location• Operations always on registers/immediates

Review: Single cycle datapath

Control

Datapath

Memory

ProcessorInput

Output


A Summary of the Control Signals (2/2)

add sub ori lw sw beq jump

RegDst

ALUSrc

MemtoReg

RegWrite

MemWrite

nPCsel

Jump

ExtOp

ALUctr<2:0>

1

0

0

1

0

0

0

x

Add

1

0

0

1

0

0

0

x

Subtract

0

1

0

1

0

0

0

0

Or

0

1

1

1

0

0

0

1

Add

x

1

x

0

1

0

0

1

Add

x

0

x

0

0

1

0

x

Subtract

x

x

x

0

0

0

1

x

x

op target address

op rs rt rd shamt funct

061116212631

op rs rt immediate

R-type

I-type

J-type

add, sub

ori, lw, sw, beq

jump

func

op 00 0000 00 0000 00 1101 10 0011 10 1011 00 0100 00 0010Appendix A10 0000See 10 0010 We Don’t Care :-)


32

ALUctr =

Clk

busW

RegWr =

3232

busA

32busB

55 5

Rw Ra Rb32 32-bitRegisters

Rs

Rt

Rt

RdRegDst =

Exten

der

Mu

x

Mux

3216imm16

ALUSrc =

ExtOp =

Mu

x

MemtoReg =

Clk

Data InWrEn

32Adr

DataMemory

32

MemWr =A

LU

InstructionFetch Unit

Clk

Zero

Instruction<31:0>

0

1

0

1

01<

21:25>

<16:20>

<11:15>

<0:15>

Imm16RdRsRt

• New PC = { PC[31..28], target address, 00 }

nPC_sel=

The Single Cycle Datapath during Jump

op target address02631

J-type jump25

Jump=

<0:25>

TA26


The Single Cycle Datapath during Jump

32

ALUctr =x

Clk

busW

RegWr = 0

3232

busA

32busB

55 5


Rs

Rt

Rt

RdRegDst = x

Exten

der

Mu

x

Mux

3216imm16

ALUSrc = x

ExtOp = x

Mu

x

MemtoReg = x

Clk

Data InWrEn

32Adr

DataMemory

32

MemWr = 0A

LU


Clk

Zero

Instruction<31:0>

0

1

0

1

01<

21:25>

<16:20>

<11:15>

<0:15>

RdRsRt

• New PC = { PC[31..28], target address, 00 }

nPC_sel=0

Jump=1

Imm16

<0:25>

TA26

op target address02631

J-type jump25


Instruction Fetch Unit at the End of Jump

Adr

InstMemory

Ad

derA

dder

PC

Clk

00Mu

x

4

nPC_sel

imm

16

Instruction<31:0>

0

1

Zero

nPC_MUX_sel

• New PC = { PC[31..28], target address, 00 }op target address

02631J-type jump

25

How do we modify thisto account for jumps?

Jump


Instruction Fetch Unit at the End of Jump

Adr

InstMemory

Ad

derA

dder

PC

Clk00

Mu

x

4

nPC_sel

imm

16

Instruction<31:0>

0

1

Zero

nPC_MUX_sel

• New PC = { PC[31..28], target address, 00 }op target address

02631J-type jump

25

Mu

x1

0

Jump

TA

26

4 (MSBs)

00

Query• Can Zero still get asserted?

• Does nPC_sel need to be 0? • If not, what?


Build CL to implement Jump on paper now

Jump

Inst31Inst30Inst29Inst28Inst27Inst26Inst25

Inst01Inst00


Review: Finite State Machine (FSM)

• States represent possible output values.

• Transitions represent changes between statesbased on inputs.

• Implement with CL andclocked registerfeedback.


Finite State Machines extremely useful!

• They define •How output signals respond to input signals and previous state.

•How we change states depending on input signals and previous state

• The output signals could be our familiar control signals•Some control signals may only depend on CL, not on state at all…

• We could implement very detailed FSMs w/Programmable Logic Arrays


Taking advantage of sum-of-products

• Since sum-of-products is a convenient notation and way to think about design, offer hardware building blocks that match that notation

• One example isProgrammable Logic Arrays (PLAs)

• Designed so that can select (program) ands, ors, complements after you get the chip• Late in design process, fix errors, figure out what to do later, …


• • •

inputs

ANDarray

• • •

outputs

ORarrayproduct

terms

Programmable Logic Arrays

• Pre-fabricated building block of many AND/OR gates• “Programmed” or “Personalized" by making or

breaking connections among gates

• Programmable array block diagram for sum of products form

And Programming:• How many inputs?• How to combine inputs?• How many product terms?

Or Programming:• How to combine product terms?• How many outputs?


example:

F0 = A + B' C'F1 = A C' + A BF2 = B' C' + A BF3 = B' C + A

personality matrix1 = uncomplemented in term0 = complemented in term– = does not participate

1 = term connected to output0 = no connection to output

input side: 3 inputs

output side: 4 outputsProduct inputs outputsterm A B C F0 F1 F2 F3

AB 1 1 – 0 1 1 0B'C – 0 1 0 0 0 1AC' 1 – 0 0 1 0 0B'C' – 0 0 1 0 1 0A 1 – – 1 0 0 1 reuse of terms;

5 product terms

Enabling Concept• Shared product terms among outputs


Before Programming

• All possible connections available before “programming”


A B C

F1 F2 F3F0

AB

B'C

AC'

B'C'

A

After Programming• Unwanted connections are "blown"

• Fuse (normally connected, break unwanted ones)

• Anti-fuse (normally disconnected, make wanted connections)


notation for implementingF0 = A B + A' B'F1 = C D' + C' D

AB+A'B'CD'+C'D

AB

A'B'

CD'

C'D

A B C D

Alternate Representation

• Short-hand notation--don't have to draw all the wires• X Signifies a connection is present and

perpendicular signal is an input to gate


Peer Instruction

A. MemToReg=‘x’ & ALUctr=‘sub’. SUB or BEQ?

B. ALUctr=‘add’. Which 1 signal is different for all 3 of: ADD, LW, & SW? RegDst or ExtOp?

C. “Don’t Care” signals are useful because we can simplify our PLA personality matrix. F / T?

ABC1: SRF2: SRT3: SEF4: SET5: BRF6: BRT7: BEF8: BET

32

ALUctr

Clk

busW

RegWr

3232

busA

32busB

55 5


Rs

Rt

Rt

Rd

RegDst

Exten

der

Mu

x

Mux

3216imm16

ALUSrc

ExtOp

Mu

x

MemtoReg

Clk

Data InWrEn

32Adr

DataMemory

32

MemWr

AL

U


Clk

Zero

Instruction<31:0>

0

1

0

1

01

<21:25>

<16:20>

<11:15>

<0:15>

Imm16RdRsRt

nPC_sel


°5 steps to design a processor• 1. Analyze instruction set => datapath requirements• 2. Select set of datapath components & establish clock

methodology• 3. Assemble datapath meeting the requirements• 4. Analyze implementation of each instruction to

determine setting of control points that effects the register transfer.• 5. Assemble the control logic

°Control is the hard part°MIPS makes that easier• Instructions same size• Source registers always in same place• Immediates same size, location• Operations always on registers/immediates

And in Conclusion… Single cycle control

Control

Datapath

Memory

ProcessorInput

Output

cs61c l27 single cycle cpu control ii (1) garcia © ucb lecturer psoe dan garcia ddgarcia...

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