The Control Unit - Hampden-Sydney Collegepeople.hsc.edu/faculty-staff/robbk/Coms361/Lectures... · 2019. 11. 12. · Outline 1 The Data Path 2 Instruction Formats 3 The Control Unit

The Control UnitLectures 31

Section 4.3, Appendix D

Robb T. Koether

Hampden-Sydney College

Mon, Nov 11, 2019

Robb T. Koether (Hampden-Sydney College) The Control Unit Mon, Nov 11, 2019 1 / 27

1 The Data Path

2 Instruction Formats

3 The Control Unit

4 R-Type Instructions

5 I-Type Instructions

6 Assignment


Outline

1 The Data Path


3 The Control Unit



6 Assignment


The Five Stages of the Data Path

The five stages.Instruction fetch (IF).Instruction decode (ID).Execution (EXE).Memory access (MEM).Write back (WB).


The Data Path

The Data Path

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

0

1

MUX

0

1

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

ALUSrc

ALUop MemWrite

MemtoReg

MemRead

RegWrite

PCSrc


Outline

1 The Data Path


3 The Control Unit



6 Assignment


Instruction Formats

MIPS uses three different formats for its instructions.R-format: 2 source registers, 1 destination registerI-format: 1 source register, 1 destination register, 1 immediate valueJ-format: 1 immediate value


Instruction Formats

Instruction Formatsle

31 2526 1621 11 5101520 06

Op code Src Reg 2Src Reg 1 Dst Reg Const Funct

R-format


Instruction Formats


31 2526 1621 1520

Op code Dst RegSrc Reg Const

0

I-format


Instruction Formats


31 2526 0

Op code Const

J-format


Outline

1 The Data Path


3 The Control Unit



6 Assignment


The Control Unit

Given the instruction, the control unit generates the control signalsneeded for the proper execution of the instruction.We will design a control unit for our sample instruction set.

lwswbeqaddiandornoraddsubslt

Our control unit will also produce the ALU control input for eachinstruction.


The Control Unit

The control unit sends out the ALU operation and seven controlsignals.

RegDst - Whether rd is the destination register.Branch - Whether the operation is a branch.MemRead - Whether to read from memory.MemtoReg - Whether the result is from the ALU or from memory.MemWrite - Whether to write to memory.ALUSrc - Whether to use an immediate value.RegWrite - Whether to write to a register.


The Control Unit

SignalName Effect When Asserted (1) Effect When Disasserted (0)RegDst The register destination The register destination

comes from the rd field comes from the rt fieldBranch PC is computed from PC← PC + 4

branch targetMemRead Put memory data in read Nothing

data outputMemtoReg The register write data The register write data

input comes from memory input comes from the ALUMemWrite Data memory replaced by Nothing

value from registerALUSrc Second operand comes from Second operand comes from

the immediate field the rt fieldRegWrite The write register is Nothing

is written with write data


The Control Unit

The Control Unit

RegWriteRegDest MemToReg MemRead MemWriteALUSrc Branch

Control Unit ALUOp ALUOp

Operation

RegWriteRegDest MemToReg MemRead MemWriteALUSrc Branch

Data Path

ALU

Instruction

32 6 6[31:26] [5:0]

2

4

The control unit sends outputs signals that control the data path.


Outline

1 The Data Path


3 The Control Unit



6 Assignment


R-Type Instructions

Consider the R-type instructionadd rd, rs, rt

Reads the values from the registers rs and rt.Adds them together.Writes the result to the register rd.


R-Type Instructions

R-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0

1Instruction [15-11]

Instruction [20-16]

Instruction [25-21]

Instruction [31-26]

RegDstBranchMemReadMemtoRegALUOpMemWriteALUSrcRegWrite

Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

0

add rd, rs, rt


R-Type Instructions

R-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Fetch


R-Type Instructions

R-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Decode


R-Type Instructions

R-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Execution


R-Type Instructions

R-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Memory Access


R-Type Instructions

R-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Write Back


Outline

1 The Data Path


3 The Control Unit



6 Assignment


I-Type Instructions

Consider the I-type instructionaddi rt, rs, imm

Reads the value from the register rs.Adds imm to that value.Writes the result to the register rt.


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

0

addi rt, rs, imm


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Fetch


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Decode


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Execution


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Memory Access


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Write Back


I-Type Instructions

Consider the I-type instructionlw rt, offset(rs)

Reads the value from the register rs.Sign-extends the offset.Adds the offset to the value from rs.Reads from that address of memory.Writes the result to the register rt.


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

0

lw rt, offset(rs)


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Fetch


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Decode


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Execution


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Memory Access


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Write Back


I-Type Instructions

Consider the I-type instructionsw rt, offset(rs)

Reads the value from the register rs.Sign-extends the offset.Adds the offset to the value from rs.Reads from that address of memory.Writes the result to the register rt.


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

0

sw rt, offset(rs)


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Fetch


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Decode


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Execution


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Memory Access


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Write Back


I-Type Instructions

Consider the I-type instructionbeq rs, rt, offset

Reads the values from the registers rs and rt.Subtracts one from the other.Produces 0 if they are equal.Shifts the offset by 2 positions.Adds the shifted offset to the PC register.


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

0

beq rs, rt, offset


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Fetch


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Instruction Decode


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Execution


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Memory Access


I-Type Instructions

I-Type Instruction

16

ALUzero

ALUresult Address

Writedata

Datamemory

Readdata

MUX

1

0

MUX

0

1

ALUcontrol

Readdata 1

Readdata 2

Registers

Readregister 1

Readregister 2

Writeregister

Writedata

Sign-extend

32

Instruction [5-0]

Instruction [15-0]

MUX

0


Instruction [20-16]

Instruction [25-21]

Instruction [31-26]


Control

ADDERADDER

Readaddress

Instruction [31-0]

Instructionmemory

PC

4

MUX

0

1

Shiftleft 2

Write Back


Outline

1 The Data Path


3 The Control Unit



6 Assignment


Assignment

AssignmentRead Section 4.3, Appendix D.


Documents

The Control Unit - Hampden-Sydney Collegepeople.hsc.edu/faculty-staff/robbk/Coms361/Lectures... · 2019. 11. 12. · Outline 1 The Data Path 2 Instruction Formats 3 The Control Unit