MIPS Assembly Language I

Tom Kelliher, CS 220

Dec. 1, 2003

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Assignment

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Outline

  1. Arithmetic and logical instructions.

  2. Instruction operands.

  3. Instruction formats.

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Conditional execution.

Arithmetic and Logical Instructions

Instruction Semantics

add a, b, c        # This, BTW, is a comment.
sub a, a, b
addi a, a, 100
and a, b, c
andi a, a, 32000
De-compile each of the following: 
add a, b, c
add a, a, d
add a, a, e
De-compile further into a single HLL statement.

Compile each of the following: 

a = b + c;
d = a - e;
f = (g + h) - (i + j);

Operands are registers.

Instruction Operands

Properties of registers:

  1. Number of registers. 32 for MIPS, including the hardwired register. Two ways of naming: numbers, convention ``nicknames''.

  2. Number of bits/register. 32. Word size.

    Implications: size of address space, datapath width.

Using MIPS Registers

Recall: 

f = (g + h) - (i + j);
Assume f through j are in $1 through $5, respectively. Compile the statement.

Memory Addressing

  1. HLL have complex data structures such as arrays and structs. How are they handled?

  2. Data transfer instructions: load, store. operands: memory address, register.

  3. Actual MIPS instructions: lw, sw.

    Base and offset addressing: lw $s0, 8($s1)

  4. MIPS memory is byte addressable, so word addresses differ by 4:

Compile the following: 

g = h + A[8];
where g is in $s1, h is in $s2, and the base address of A, an array of 100 words, is in $s3.

Base, offset addressing.

Compile each of the following: 

A[12] = h + A[8];

A[j] = h + A[i];

Base, offset addressing, using constant offsets, is similarly useful for accessing members of structures.

Instruction Formats

MIPS R-Format

Example instruction: add $s2, $s0, $s1

Fields:

  1. Op: Opcode.

  2. Rs: First source operand.

  3. Rt: Second source operand.

  4. Rd: Destination operand.

  5. Shamt: Shift amount --- ignore for now.

  6. Func: Function. Further specification of the opcode.

In assembly: Op/Func Rd, Rs, Rt

Notes:

  1. Example encodings:

MIPS I-Format

Example instruction: lw $s0 8($s1)

Fields:

  1. Op: Opcode.

  2. Rs: Source register.

  3. Rt: Destination register.

  4. Address: 16-bit signed immediate value.

    Offset range?

In assembly: Op/Func Rt, address(Rs)

Notes:

  1. This format also used for immediate operands: addi $1, $2, 123.

  2. Example encodings:


Thomas P. Kelliher
Tue Nov 25 11:03:35 EST 2003
Tom Kelliher