[컴퓨터구조] 2. Instructions: Language of the Computer (2)

MIPS

 

RISC vs. CISC

• RISC: Reduced Instruction Set Computer
• CISC: Complex Instruction Set Computer

RISC vs. CISC

 

MIPS R2000 CPU and FPU

• CPU
• Two coprocessors: Coprocessor 0, Coprocessor 1

MIPS processor

 

CPU (Central Processing Unit)

• ALU(Arithmetic Logic Unit): Performs arithmetic and logic operations.
• Control unit: Extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

 

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Registers

▶ MIPS --> 32 registers

• 31 of these are general-purpose registers that can be used in any of the instructions.
• The last one, denoted register "zero" is defined to contain the number zero at all times.

MIPS Register Set (32 Registers)

 

MIPS Instruction Set

• "o" --> Assembler: Traslates pseudo-instructions into one or more native instructions.
• "u" --> "unsigned"
  - add: add signed
  - addu: add unsigned
• Operation(연산): Specifies what function to perform.
  Operand(피연산자): Specifies with what a specific function is performed.

▶ MIPS operation

• Arithmetic operations (integer, floating-point)
• Logical operations
• Shift operations
• Compare operations
• Load/Store to transfer data from/to memory.
• Branch/Jump operations
• System control/Coprocessor operations

 
▶ MIPS operands

• General-purpose registers
• Fixed registers (예: HI/LO registers)
• Memory location
• Immediate value

 

MIPS Instruction

• Destination: register
• Source 1: register
• Source 2: register | 32-bit integer
• Register 2: register
• Address: memory address

 

Load Instructions

: Fetch a byte, halfword, word from memory and put it into a register.

• Byte: 8 bits
• Word: 4 bytes --> 32 bits
• Halfword: 2 bytes --> 16 bits

Load Instruction

li    $t1, 1           # load 1 into $t1

 

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Arithmetic Instructions

Arithmetic Instructions

 

Arithmetic Examples

: <op> <destination> <source 1> <source 2>

add  $t0, $s0, $s2       # $t0 = $s0 + $s2

 

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Syscalls

Syscalls

 

Syscalls - Example

li     $v0, 10         
syscall                # v0 == 10 --> Exit

li   $v0, 5
syscall           # $v0 == 5 --> read_int
move $t0, $v0     # Move the number read from $v0 to $t0 (안전한 장소로 옮기는 것)

move  $a0, $t2     # move the number from $t2 to $a0
li    $v0, 1
syscal             # $v0 = 1 --> Print $a0

 

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Data Movement Instructions

Data Movement Instructions

 

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Program Template

Program Template

 

Two Sections

▶ Data: Where the variables are declared.
▶ Text: Instructions go here.

• Contains the beginning of the program.

 

Directives

: Instruction for the assembler for reserving memory, telling the assembler where to place instructions ...etc
▶ Data segment

• Tagged with the .data directive.
• Used to allocate storage and initialize global variables.

▶ Text segment

• Indicated by the .text directive.
• Where we put the instructions we want the processor to execute.

--> Assembler starts in the text segment.
 

Example 1

Example 1

 

Comments

• # (pound sign)

 

Labels and Main

• main: Program execution begins at the location with the label "main".

** label: Symbolic name for address in memory.
 

Example 2

Example 2

Cf) $t0 == 5, $t1 == 5라고 가정한 것
 

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SBY 3-1

li   $a0, 10      # load_int $a0, 10
li   $v0, 1       # load_int $v0, 1
syscall           # $v0 == 1 --> Print $a0 --> Print 10

 
 

li   $v0, 5        
syscall           # read_int
move $t0, $v0     # move from $v0 to $t0

li   $v0, 5        
syscall           # read_int
move $t1, $v0     # move from $v0 to $t1

li   $v0, 5        
syscall           # read_int
move $t2, $v0     # move from $v0 to $t2

add  $t3, $t0, $t1   # $t3 = $t0 + $t1
add  $t3, $t3, $t2   # $t3 = $t3 + $t2

move $a0, $t3     # move from $t3 to $a0
li   $v0, 1      
syscall           # $v0 == 1 --> print $a0

li   $v0, 10      
syscall           # $v0 == 1 --> exit

$v0 = 5 ; 상수 5를 $v0 저장하고 나서 syscall을 부르기에, $v0 = 5는 syscall code 5를 하기 위함.. 

즉 read_int 를 하려고 저렇게 한 것이고,

그렇게 syscall이후에 다시 실행되는 move $t0, $v0 의 $v0는 이제 이전의 5가 들어있는 것이 아니고,

사용자가 콘솔에서 입력값으로 입력한 정수값 (예를 들어, 콘솔에서 내가 15를 타이핑한 후 엔터를 쳤다면) $v0 에 이제 15가 저장이 된 후에, syscall 이후의 프로그램이 이제 실행되게 됩니다.

 

$v0의 용도가 syscall 코드 셋팅으로도 사용되고, read인 경우 사용자가 콘솔에서 입력한 값으로도 또 바뀌기 때문에,

그래서 move $t0, $v0를 통해 $t0 로 잘 저장해 놓는 것입니다.