MIPS ISA and MIPS Assembly CS301 Prof. Szajda Administrative HW - - PowerPoint PPT Presentation

MIPS ISA and MIPS Assembly

CS301

• Prof. Szajda

Administrative

• HW #2 due Wednesday (9/11) at 5pm
• Lab #2 due Friday (9/13) 1:30pm
• Read Appendix B5, B6, B.9 and Chapter

2.5-2.9 (if you have not already done so!)

MIPS ISA

MIPS ISA

• Small number of simple instructions (RISC)

w Instructions are fixed size of 32b w Very rigid structure

• Load/Store Architecture

w Few addressing modes

Register File

• Register file

w 32 integer w 32 single precision floating point

• Integer

w Volatile - scratch registers

§ $t0 - $t9 ($8-$15, $24-$25)

w Non-volatile - called function does save/ restore

§ $s0 - $s7 ($16-$23)

What’s going on here?!

Special Integer Registers

• Zero

w $0

• Return values

w $v0, $v1 ($2, $3)

• Function arguments

w $a0-$a3 ($4-$7) w If more than 4 registers required, then place parameters “above” frame pointer (at higher address)

• Stack pointer - $sp ($29)
• Frame pointer - $fp ($30)

w Usually not used in our examples

• Return address - $ra ($31)

Floating Point Registers

• 32 single-precision registers

w $f0, $f1, ..., $f31

• Double precision uses 2 single precision fp registers

w reference even numbered registers

• Special registers

w Return values

§ $f0-$f3

w Function arguments

§ $f12 - $f15

Data Movement Instructions

• move rd, rs

w Move register rs to rd

• mov.d fd, fs

w Move double precision fp register fs to fd

• mtc1 fd, rs

w Move rs register to fd

• mfc1 rd, fs

w Move fp register fs to rd

move to coprocessor 1 move from coprocessor 1

Load/Store Instructions

• la rt, address

w load computed address (not contents of location) into register rt

• lw rt, address

w load word in memory location address into register rt

• sw rt, address

w store value in register rt into memory at location address

• li rt, imm

w load integer constant imm into register rt

• l.d rt, address

w load double precision fp value from memory location address into fp register rt and rt+1

Arithmetic Instructions

• add rd, rs, rt

w rd = rs + rt

• addi rd, rs, imm

w rd = rs + imm

• sub rd, rs, rt

w rd = rs - rt

• mul rd, rs, rt

w rd = rs × rt

• div rd, rs, rt

w rd = rs / rt

• Floating point versions exist usually with a .d tacked
• n (add.d)

multiply (without overflow) puts low order 32 bits of product in rd divide (without overflow)

Shift Operators

• sll rd, rt, sa

w rd = rt << sa w Zero fill

• sra rd, rt, sa

w rd = rt >> sa w Sign fill

• srl rd, rt, sa

w rd = rt >> sa w Zero fill

shift left logical shift right arithmetic shift right logical

Comparison Instructions

• slt rd, rs, rt

w Set register rd to 1 if rs < rt, otherwise set rd to 0

• slti rd, rs, imm

w Set register rd to 1 if rs < imm, otherwise set rd to 0

• Similar instructions for greater than
• seq rd, rs, rt

w Set rd to 1 if rs == rt, otherwise set rd to 0

Branch Instructions

• 16-b instruction ofgset field (215-1

forward, 215 back)

• b label

w Unconditionally branch to instruction at label

• beq rs, rt, label

w Conditionally branch to label if rs == rt

• bne, bgt, bge, ...

Jump Instructions

• 26-bit address field
• j target

w Unconditionally jump to instruction at target

• jal target

w Unconditionally jump to instruction at target w Save address of next instruction in register $ra w bal is like jal however jal must be used if target is from another file

jump and link

Assembly Programs

Note:

You will only be allowed to use the instructions listed in Appendix B.10 in your programs!

16

# assign.asm # simple program to modify a global variable .data # add what follows to the data section x: .word 5 # create global integer variable x. Set to 5. .text # add what follows to the text .align 2 # Align on word boundaries .globl main # "exports" the symbol main so it is # accessible to other modules main: # we don't need a frame la $t0, x # $t0 = &x lw $t1, 0($t0) # $t1 = x addi $t1,$t1,2 # $t1 = $t1 + 2 sw $t1, 0($t0) # x = $t1 jr $ra # return - main is a function, too

Assembly File

• Segments

w .data

§ Integer (.word), character (.byte), arrays of these, § String (.asciiz)

w .text

§ Instructions § main should be first instruction and needs to be specified as .globl

the “z” is required if you want your string to be null terminated! an “assembler directive”

MIPS Labels

• MIPS assembly code contains instructions
• Data and instructions can be prefaced with a label

followed by a colon

w main:

• Instructions can have operands that are:

w registers w constants/immediates w addresses

§ Explicit numbers § Register + ofgset § Labels

• Assembler will replace labels with corresponding

addresses when creating machine language

Examples

Suppose $s0 = a, $s1 = b, $s2 = c, $s3 = d

• Write MIPS instructions for the

following code:

b = (c - 1) × (a + d)

Examples

Suppose $s0 = a, $s1 = b, $s2 = c, $s3 = d

• Write MIPS instructions for the following code:

if(a > b) c = c+1; else d = d+1;

Examples

Suppose A is an array of 10 integers

w How would I declare A as a global array?

Suppose $s0 = A, $s1 = g, $s2 = h, $s3 = i

• Write MIPS instructions for the following code:

g = h +A[i];

Using Strings

• ASCII

w 8-bit used to represent characters

• To access individual characters, use

w lb $t0, 0($sp) # read character w sb $t0, 0($sp) # write character

• Strings

w Array of characters w Terminated with byte whose value is 0 (null)

Examples

Suppose A is a string

w How would I declare A as a global variable?

Suppose $s0 = A, $s1 = g, $s2 = h, $s3 = i

• Write MIPS instructions for the following code:

g = A[i];