EEE 105 Lab Exercise

7/24/2019 EEE 105 Lab Exercise

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EEE 105: Computer Organization

Lab 3: MIPS Subroutines/Functions

University of the PhilippinesElectrical and Electronics Engineering Institute


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Function/Subroutine

Function fundamental unit of programming

gives a simple form of program abstraction

allows reuse of codes In assembly language, a function is

referred to as subroutine.


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Subroutine

A subroutine can be called anywhere inthe program.

Once execution of subroutine is complet

program execution should return to thelocation that called the subroutine.


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Subroutine

Sets up the arguments forthe subroutine

Calls the subroutine

Caller Subroutine

arguments

returnvalues

Uses the arguments toperform somecomputations.

Returns the results to tcaller.


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Calling Subroutines in MIPS

Two important instructionsjal label

Copies the address of the next instruction inregister $ra and then jumps to address label

jr $register

Jumps execution to the address in register$register. Use register $ra if returning

execution to caller.


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Register Convention $v0-$v1

Return values of subroutines (not preserved)

$a0-$a3 Argument registers, used by the caller to pass data

subroutine

$t0-$t9 Temporary registers, can be used inside the

subroutines

$s0-$s7

Saved registers, these registers should be preserveacross function calls


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Subroutine Example 1main: lw $a0, 0x2000($zero)

lw $a1, 0x2004($zero)

jal mult #no negative inputs

j end_main

mult: add $v0, $zero, $zero #clear reg for output

loop: beq $a1, $zero, end

add $v0, $v0, $a0 #update output

addi $a1, $a1, -1 #input $a1 is not pres

j loop

end: jr $ra

end_main:


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MIPS Calling Convention

Allocate memory and save the valueof registers ($ra, $a0, $s0, etc.)

Load the original value of registers($ra, $a0, $s0, etc) from memory

Do some things here

End the function and return


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Stack

Good for storing large and variable length d

LIFO (last in, first out) data structure Uses push/pop operations to change the top of

stack

May not be followed based on the context and long as you know what you are doing

Implementation-dependent Top-of-stack may either point to the last item or

next free slot For our class, the TOS points to the next free s


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Stack

INACTIVE

FRAME(N-3)

DATA 0x3FFC STACK ORIGIN

DATA 0x3FF8

DATA 0x3FF4

INACTIVEFRAME

(N-2)

RETURN ADDRESS to N-3 0x3FF0

DATA 0x3FEC

DATA 0x3FE8

INACTIVEFRAME

(N-1)

RETURN ADDRESS to N-2 0x3FE4

DATA 0x3FE0

DATA 0x3FDC

ACTIVEFRAME

(N)

RETURN ADDRESS to N-1 0x3FD8

DATA

DATA

DATA

AVAILABLE or

UNUSEDSTACK SPACE

STACK POINTER

0x3004

0x3000


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Stack on MARS Stack is filled from top to bottom

Memory address 0x00003FFF down to 0x00003000 Memory Configuration: Compact, Text at Address 0

$sp initializes at 0x00003FFC 0x00003FFF is not a word address

Data Address (word aligned)FF FE FD FC 0x00003FFC

FB FA F9 F8 0x00003FF8

F7 F6 F5 F4 0x00003FF4

07 06 05 04 0x00003004

03 02 01 00 0x00003000

Data Address (word aligned)

xxxx 0x00003FFC

xxxx 0x00003FF8

xxxx 0x00003FF4

xxxx 0x00003004

xxxx 0x00003000

Data Address (word aligned)0x0000FFFF 0x00003FFC

xxxx 0x00003FF8

xxxx 0x00003FF4

xxxx 0x00003004

xxxx 0x00003000


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Stack Example

subroutine:

add $a0, $ra, $zerojal push #save return address

. . .

#call other subroutines

. . .

jal pop #retrieve return address

jr $v0

push: sw $a0, 0($sp) # store data from $a0

addi $sp, $sp, -4 # $sp is updated to point to the ne

jr $ra # free address

pop: lw $v0, 4($sp) # load data to $v0

addi $sp, $sp, 4 # $sp is updatedjr $ra

Relative Addre

Use data storedaddress stored w/ offset


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MIPS Example 2

main: lw $a0, 0x2000($zero)

lw $a1, 0x2004($zero)lw $a2, 0x2008($zero)

jal mult3

j end

mult: sw $a1, 0($sp)

addi $sp, $sp, -4

add $v0, $zero, $zero

m_loop: beq $a1, $zero, m_end

add $v0, $v0, $a0

addi $a1, $a1, -1

j m_loop

m_end: addi $sp, $sp, 4

lw $a1, 0($sp)jr $ra

mult3: sw $ra, 0($sp)

sw $a0, -4($sp)sw $a1, -8($sp)

addi $sp, $sp, -12

jal mult

add $a0, $v0, $zero

add $a1, $a2, $zerojal mult

addi $sp, $sp, 12

lw $a1, -8($sp)

lw $a0, -4($sp)

lw $ra, 0($sp)

jr $ra


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ME 3 OverviewCreate an assembly program in MARS that

gets an input (greater than 1) from the memory address0x00002000 (memory configuration 3)

stores in the stack (starting at 0x00003FFC downwards) thprime factors of the input $sp should point to the next free address

Examples:

N = 90

Data Address

2 0x00003FFC

3 0x00003FF8

3 0x00003FF45 0x00003FF0

$sp = 0x00003FEC

N = 391

Data Address

17 0x00003FFC

23 0x00003FF8

$sp = 0x00003FF4


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ME3 Specifications Given:

isprime subroutine

input $a0 (retained) output $v0 0 if not prime, 1 if prime all registers are preserved aside from $v0

Algorithm for the prime factorization

Tasks mod_div subroutine

input $a0 for dividend, $a1 for divisor output $v0 for the remainder, $v1 for the quotient all registered are preserved aside from $v0 and $v1 Note: the mod_div subroutine is called by the isprime subroutine

Implementation of the prime factorization algorithm Not strict but must use the isprime subroutine at the very least

Multiply, divide, square root and pseudo instructions are not allowed

INPUT OUTPUT

N > 1(32-bit number)

Prime facto

0x2000Stack: 0x3F

downward


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Prime Factorization Algorithm

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EEE 105 Lab Exercise