Computer Architecture Lecture 9: MIPS Instruction Set

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Questions and Answers

What is the format of the instruction beq rs, rt, label?

op6 = 4, rs5, rt5, imm16

What is the result of the instruction slt $t0,$s1,$s0 when $s0 = 1 and $s1 = -1 = 0xffffffff?

$t0 = 1

What is the purpose of the 'sa' field in MIPS instructions?

Specifies the shift amount

What is the result of the instruction sltu $t0,$s0,$s1 when $s0 = 1 and $s1 = -1 = 0xffffffff?

$t0 = 0 Signup and view all the answers

What is the meaning of the instruction bgez rs, label?

branch if rs >= 0 Signup and view all the answers

What is the difference between the 'add' and 'addu' instructions?

Addu does not cause an arithmetic exception, while add does. Signup and view all the answers

What is the format of the instruction j label?

op6 = 2, imm26 Signup and view all the answers

What is the purpose of the 'funct' field in MIPS instructions?

Specifies the function code Signup and view all the answers

What is the purpose of the 'Op' field in MIPS instructions?

Specifies the operation code Signup and view all the answers

What is the meaning of the instruction bltz rs, label?

branch if rs < 0 Signup and view all the answers

How many registers are there in MIPS32?

32 general-purpose registers Signup and view all the answers

What is the purpose of the 'Rs' and 'Rt' fields in MIPS instructions?

Specify the source registers Signup and view all the answers

What is the purpose of the ' Rd' field in MIPS instructions?

Specifies the destination register Signup and view all the answers

What is the difference between the 'and' and 'nor' instructions?

And is used for bitwise AND, while nor is used for bitwise NOR Signup and view all the answers

What is the purpose of the 'immediate' field in I-Type instructions?

Specifies a 16-bit immediate constant Signup and view all the answers

How many instruction formats are there in MIPS?

3 Signup and view all the answers

What is the purpose of the `sll` instruction in MIPS?

To shift the bits of the register left Signup and view all the answers

How can you multiply a number by 36 using shift and add instructions?

By factoring 36 into (4 + 32) and using the distributive property of multiplication Signup and view all the answers

What is the purpose of the `mult` instruction in MIPS?

To perform signed multiplication Signup and view all the answers

What is the purpose of the `mflo` instruction in MIPS?

To move data from LO to a register Signup and view all the answers

What is the limitation of the R-type shift instructions in MIPS?

They have a 5-bit shift amount constant Signup and view all the answers

How can you multiply a number by 31 using shift and add instructions?

By shifting left by 5 and subtracting the original number Signup and view all the answers

What is the purpose of the `div` instruction in MIPS?

To perform signed division Signup and view all the answers

What happens if the divisor is 0 in a division operation in MIPS?

The result is unpredictable Signup and view all the answers

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Study Notes

MIPS Instruction Set Architecture

MIPS is a type of Reduced Instruction Set Computer (RISC)
All instructions are typically 32-bits wide
Arithmetic instructions are register-to-register, operands are read from registers, and the result is stored in a register
MIPS has 32 general-purpose integer and 32 floating-point registers

General Purpose Registers (GPRs)

There are 32 GPRs in MIPS, each 32-bits wide
The assembler uses the dollar notation to name registers, e.g., 0,0, 0,1, ..., $31
Register $0 is always zero, and any value written to it is discarded

Register Naming Convention

Software defines names for registers to standardize their use in programs
Registers 8−8-8−15 are called t0−t0-t0−t7, used for temporary values
Registers 16−16-16−23 are called s0−s0-s0−s7, used for saved registers
Registers have specific names and uses, such as v0−v0-v0−v1 for result values, a0−a0-a0−a3 for arguments, and $ra for return addresses

Instruction Format

There are three instruction formats: R-type, I-type, and J-type
R-type format is used for register-to-register instructions
I-type format is used for instructions with a 16-bit immediate constant
J-type format is used for jump instructions

Instruction Examples

Arithmetic instructions: add, addu, sub, subu, with R-type format
Logical instructions: and, or, xor, nor, with R-type format
Shift instructions: sll, srl, with R-type format and a 5-bit shift amount field
Jump and branch instructions: j, beq, bne, blez, bltz, bgez, with J-type format

Shifting and Multiplication

Shifting can be used to perform multiplication by a power of 2
Example: multiplying $s1 by 36 using sll and add instructions

Assignment

Multiply $s1 by 26 using shift and add instructions
Multiply $s1 by 31 using shift and sub instructions

Multiplication and Division

Signed and unsigned multiplication: mult, multu, with a 64-bit result
Signed and unsigned division: div, divu, with a 32-bit quotient and remainder
Moving data between LO and HI registers and general-purpose registers

Constants

Constants are used frequently in programs
R-type shift instructions have a 5-bit shift amount constant
Other instructions may need a constant, but the method is not specified