1 COMS 361 Computer Organization Title: Instructions Date: 9/28/2004 Lecture Number: 10.

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COMS 361Computer Organization

Title: Instructions

Date: 9/28/2004

Lecture Number: 10

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Announcements

• Homework 4– Due 10/05/04

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Review

• Instructions– unconditional branch– J-Type instruction format

• MIPS history

• SPIM– MIPS simulator

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Outline

• SPIM– MIPS simulator

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SPIM Program

• Show me the code!• MIPS/SPIM program files usually end in .s

• File is loaded into SPIM– Assembled into MIPS machine code– Executed and debugged in SPIM

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SPIM Program## exit.s - program simply makes a system call to exit

#### text segment##

.text

main: addi $v0, $zero, 10 # exit call codesyscall # terminate program execution

#### data segment##

#### end exit.s

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#### text segment##

.text


#### data segment##

#### end exit.s

Comments in MIPS assembly code are denoted by the sharp (#) sign

Similar to the C++ (//) comment. Starts at instance and goes to the end of the line

Assembly code in NOT self-documenting. Use comments liberally, like associated with each instruction

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#### text segment##

.text


#### data segment##

#### end exit.s

Comments indicating the start of the code

After text segment is converted into its binary representation, it is stored in the text memory segment

. indicates an assembler directive

.text directs the assembler to treat what follows as instructions

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Text Segment

• The source code format is relatively standard

– Proper indentation is fundamentally important in assembly language programming

– [] indicate optional fields• Not all fields appear on a line of code

[label:] operation [operand], [operand], [operand] [# comment]

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#### text segment##

.text


#### data segment##

#### end exit.s

main: is a label

Just as C++ programs need a main function, MIPS programs need a main label

main: labels the first instruction of the program

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Labels

• : – Tells the assembler that the proceeding

alphanumerics including (_) and (.) constitutes the label

– Opcodes are reserved words and are not permitted to be used as labels

– Use appropriate names for labels

• Labels associate a symbol with– The address of an instruction– The address of a variable

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#### text segment##

.text


#### data segment##

#### end exit.s

Program is to simple call the OS with the exit call code

In the real world the OS cleans up after the program

The call code for exit is the decimal number 10, which needs to be put into the $v0 register (convention)

addi with the proper operands can achieve this goal

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#### text segment##

.text


#### data segment##

#### end exit.s

Call the OS with the proper call code in the $v0 register

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SPIM Program

• Show me the program execute!– And some things about SPIM City!!

• exit.s

• hello.s

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Datapath Diagram

• Main functional units– Control unit Program Counter (PC)

Instruction Register

Register File

ALU

Cache Memory

Data In

Address

4

Out

Rs

RtRd

ControlLogic

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Datapath Diagram

• Main functional units– Register file Program Counter (PC)


Register File

ALU

Cache Memory

Data In

Address

4

Out

Rs

RtRd

ControlLogic

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Datapath Diagram

• Main functional units– Arithmetic and logic unit (ALU) Program Counter (PC)


Register File

ALU

Cache Memory

Data In

Address

4

Out

Rs

RtRd

ControlLogic

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Datapath Diagram

• Main functional units– Program counter (PC) Program Counter (PC)


Register File

ALU

Cache Memory

Data In

Address

4

Out

Rs

RtRd

ControlLogic

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Datapath Diagram

• Main functional units– Memory Program Counter (PC)


Register File

ALU

Cache Memory

Data In

Address

4

Out

Rs

RtRd

ControlLogic

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Datapath Diagram

• Main functional units– Instruction register (IR) Program Counter (PC)


Register File

ALU

Cache Memory

Data In

Address

4

Out

Rs

RtRd

ControlLogic

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Datapath Diagram

• Other operational units– bus Program Counter (PC)


Register File

ALU

Cache Memory

Data In

Address

4

Out

Rs

RtRd

ControlLogic

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Datapath Diagram

• Other operational units– Multiplexor (data selector) Program Counter (PC)


Register File

ALU

Cache Memory

Data In

Address

4

Out

Rs

RtRd

ControlLogic

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Fetch and Execute R-type

• Instruction Fetch Phase– Fetch the word in memory at the address

specified by the Program Counter (PC)– Load instruction into the IR– Increment the PC (add 4)

• Operand Fetch Phase– Decode the Rs and Rt fields within the instruction

Decode the Op Code

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Fetch and Execute Cycle

• Execute Phase– Perform ALU operation defined by the function

code on the source operands

• Write Back Phase– Result if the ALU is written into the decoded Rd

register

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MIPS Instructions

• MIPS instruction set architecture– Assembly instructions that convert into machine

(binary) instructions• Assembly instructions can be converted directly into

machine instructions– One-to-one mapping

• Assembly instructions can be converted into more than one machine instruction

– One-to-many mapping

– Native machine instructions– Pseudo-, Macro-, Synthetic-machine instructions

• Consists of more than one native machine instruction

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MIPS Instructions

• Assembler converts pseudo-instructions with the corresponding set of actual MIPS instructions– Pseudo-instructions simplify the task of writing

assembly code

pseudo instruction la $a0 label

load address of label into register $a0

actual MIPS instructions

lui $at, upper 16 bits of label

ori $Rd, $at, Lower 16 bits of label

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Assembler Directives

• Used to create data structures that are available at run-time– To allocate a one-dimensional array in C++

int ARRAY[1024];

– Corresponds to the MIPS assemble directive

.data

ARRAY: .space 4096Allocate space in the data

segment of the SPIMmemory model

Allocates 4096 bytes in thedata segment

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– Allocate and initialize a one-dimensional arrayint ARRAY[] = { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 };

– Corresponds to the MIPS assemble directive

.data

ARRAY: .word 1, 2, 4, 8, 16, 32, 64, 128, 256, 512,

1024

la $a0 ARRAY # $a0 = &ARRAY[0]

lw $s0 8($a0) # $s0 = MEM[$ao + 8]

$a0 contains a pointer to the array

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– String literal definition

.data

helloStr: .ascii “Hello, World!\n”

– helloStr is the memory location of the array of characters

– The string is not null terminated• Can cause problems (hell01.s)

.data

helloStr: .asciiz “Hello, World!\n”

1 COMS 361 Computer Organization Title: Instructions Date: 9/28/2004 Lecture Number: 10.

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Transcript of 1 COMS 361 Computer Organization Title: Instructions Date: 9/28/2004 Lecture Number: 10.