mirror of
https://github.com/adambard/learnxinyminutes-docs.git
synced 2024-12-24 10:01:38 +00:00
380 lines
15 KiB
Markdown
380 lines
15 KiB
Markdown
---
|
||
language: "MIPS Assembly"
|
||
filename: MIPS.asm
|
||
contributors:
|
||
- ["Stanley Lim", "https://github.com/Spiderpig86"]
|
||
---
|
||
|
||
The MIPS (Microprocessor without Interlocked Pipeline Stages) Assembly language
|
||
is designed to work with the MIPS microprocessor paradigm designed by J. L.
|
||
Hennessy in 1981. These RISC processors are used in embedded systems such as
|
||
gateways and routers.
|
||
|
||
[Read More](https://en.wikipedia.org/wiki/MIPS_architecture)
|
||
|
||
```asm
|
||
# Comments are denoted with a '#'
|
||
|
||
# Everything that occurs after a '#' will be ignored by the assembler's lexer.
|
||
|
||
# Programs typically contain a .data and .text sections
|
||
|
||
.data # Section where data is stored in memory (allocated in RAM), similar to
|
||
# variables in higher-level languages
|
||
|
||
# Declarations follow a ( label: .type value(s) ) form of declaration
|
||
hello_world: .asciiz "Hello World\n" # Declare a null terminated string
|
||
num1: .word 42 # Integers are referred to as words
|
||
# (32-bit value)
|
||
|
||
arr1: .word 1, 2, 3, 4, 5 # Array of words
|
||
arr2: .byte 'a', 'b' # Array of chars (1 byte each)
|
||
buffer: .space 60 # Allocates space in the RAM
|
||
# (not cleared to 0)
|
||
|
||
# Datatype sizes
|
||
_byte: .byte 'a' # 1 byte
|
||
_halfword: .half 53 # 2 bytes
|
||
_word: .word 3 # 4 bytes
|
||
_float: .float 3.14 # 4 bytes
|
||
_double: .double 7.0 # 8 bytes
|
||
|
||
.align 2 # Memory alignment of data, where
|
||
# number indicates byte alignment
|
||
# in powers of 2. (.align 2
|
||
# represents word alignment since
|
||
# 2^2 = 4 bytes)
|
||
|
||
.text # Section that contains
|
||
# instructions and program logic
|
||
.globl _main # Declares an instruction label as
|
||
# global, making it accessible to
|
||
# other files
|
||
|
||
_main: # MIPS programs execute
|
||
# instructions sequentially, where
|
||
# the code under this label will be
|
||
# executed first
|
||
|
||
# Let's print "hello world"
|
||
la $a0, hello_world # Load address of string stored
|
||
# in memory
|
||
li $v0, 4 # Load the syscall value (number
|
||
# indicating which syscall to make)
|
||
syscall # Perform the specified syscall
|
||
# with the given argument ($a0)
|
||
|
||
# Registers (used to hold data during program execution)
|
||
# $t0 - $t9 # Temporary registers used for
|
||
# intermediate calculations inside
|
||
# subroutines (not saved across
|
||
# function calls)
|
||
|
||
# $s0 - $s7 # Saved registers where values are
|
||
# saved across subroutine calls.
|
||
# Typically saved in stack
|
||
|
||
# $a0 - $a3 # Argument registers for passing in
|
||
# arguments for subroutines
|
||
# $v0 - $v1 # Return registers for returning
|
||
# values to caller function
|
||
|
||
# Types of load/store instructions
|
||
la $t0, label # Copy the address of a value in
|
||
# memory specified by the label
|
||
# into register $t0
|
||
lw $t0, label # Copy a word value from memory
|
||
lw $t1, 4($s0) # Copy a word value from an address
|
||
# stored in a register with an
|
||
# offset of 4 bytes (addr + 4)
|
||
lb $t2, label # Copy a byte value to the
|
||
# lower order portion of
|
||
# the register $t2
|
||
lb $t2, 0($s0) # Copy a byte value from the source
|
||
# address in $s0 with offset 0
|
||
# Same idea with 'lh' for halfwords
|
||
|
||
sw $t0, label # Store word value into
|
||
# memory address mapped by label
|
||
sw $t0, 8($s0) # Store word value into address
|
||
# specified in $s0 and offset of
|
||
# 8 bytes
|
||
# Same idea using 'sb' and 'sh' for bytes and halfwords. 'sa' does not exist
|
||
|
||
### Math ###
|
||
_math:
|
||
# Remember to load your values into a register
|
||
lw $t0, num # From the data section
|
||
li $t0, 5 # Or from an immediate (constant)
|
||
li $t1, 6
|
||
add $t2, $t0, $t1 # $t2 = $t0 + $t1
|
||
sub $t2, $t0, $t1 # $t2 = $t0 - $t1
|
||
mul $t2, $t0, $t1 # $t2 = $t0 * $t1
|
||
div $t2, $t0, $t1 # $t2 = $t0 / $t1 (Might not be
|
||
# supported in some versions of MARS)
|
||
div $t0, $t1 # Performs $t0 / $t1. Get the
|
||
# quotient using 'mflo' and
|
||
# remainder using 'mfhi'
|
||
|
||
# Bitwise Shifting
|
||
sll $t0, $t0, 2 # Bitwise shift to the left with
|
||
# immediate (constant value) of 2
|
||
sllv $t0, $t1, $t2 # Shift left by a variable amount
|
||
# in register
|
||
srl $t0, $t0, 5 # Bitwise shift to the right (does
|
||
# not sign preserve, sign-extends
|
||
# with 0)
|
||
srlv $t0, $t1, $t2 # Shift right by a variable amount
|
||
# in a register
|
||
sra $t0, $t0, 7 # Bitwise arithmetic shift to
|
||
# the right (preserves sign)
|
||
srav $t0, $t1, $t2 # Shift right by a variable amount
|
||
# in a register
|
||
|
||
# Bitwise operators
|
||
and $t0, $t1, $t2 # Bitwise AND
|
||
andi $t0, $t1, 0xFFF # Bitwise AND with immediate
|
||
or $t0, $t1, $t2 # Bitwise OR
|
||
ori $t0, $t1, 0xFFF # Bitwise OR with immediate
|
||
xor $t0, $t1, $t2 # Bitwise XOR
|
||
xori $t0, $t1, 0xFFF # Bitwise XOR with immediate
|
||
nor $t0, $t1, $t2 # Bitwise NOR
|
||
|
||
## BRANCHING ##
|
||
_branching:
|
||
# The basic format of these branching instructions typically follow <instr>
|
||
# <reg1> <reg2> <label> where label is the label we want to jump to if the
|
||
# given conditional evaluates to true
|
||
# Sometimes it is easier to write the conditional logic backward, as seen
|
||
# in the simple if statement example below
|
||
|
||
beq $t0, $t1, reg_eq # Will branch to reg_eq if
|
||
# $t0 == $t1, otherwise
|
||
# execute the next line
|
||
bne $t0, $t1, reg_neq # Branches when $t0 != $t1
|
||
b branch_target # Unconditional branch, will
|
||
# always execute
|
||
beqz $t0, req_eq_zero # Branches when $t0 == 0
|
||
bnez $t0, req_neq_zero # Branches when $t0 != 0
|
||
bgt $t0, $t1, t0_gt_t1 # Branches when $t0 > $t1
|
||
bge $t0, $t1, t0_gte_t1 # Branches when $t0 >= $t1
|
||
bgtz $t0, t0_gt0 # Branches when $t0 > 0
|
||
blt $t0, $t1, t0_gt_t1 # Branches when $t0 < $t1
|
||
ble $t0, $t1, t0_gte_t1 # Branches when $t0 <= $t1
|
||
bltz $t0, t0_lt0 # Branches when $t0 < 0
|
||
slt $s0, $t0, $t1 # "Set on Less Than"
|
||
# when $t0 < $t1 with result in $s0
|
||
# (1 for true)
|
||
|
||
# Simple if statement
|
||
# if (i == j)
|
||
# f = g + h;
|
||
# f = f - i;
|
||
|
||
# Let $s0 = f, $s1 = g, $s2 = h, $s3 = i, $s4 = j
|
||
bne $s3, $s4, L1 # if (i !=j)
|
||
add $s0, $s1, $s2 # f = g + h
|
||
|
||
L1:
|
||
sub $s0, $s0, $s3 # f = f - i
|
||
|
||
# Below is an example of finding the max of 3 numbers
|
||
# A direct translation in Java from MIPS logic:
|
||
# if (a > b)
|
||
# if (a > c)
|
||
# max = a;
|
||
# else
|
||
# max = c;
|
||
# else
|
||
# if (b > c)
|
||
# max = b;
|
||
# else
|
||
# max = c;
|
||
|
||
# Let $s0 = a, $s1 = b, $s2 = c, $v0 = return register
|
||
ble $s0, $s1, a_LTE_b # if(a <= b) branch(a_LTE_b)
|
||
ble $s0, $s2, max_C # if(a > b && a <=c) branch(max_C)
|
||
move $v0, $s0 # else [a > b && a > c] max = a
|
||
j done # Jump to the end of the program
|
||
|
||
a_LTE_b: # Label for when a <= b
|
||
ble $s1, $s2, max_C # if(a <= b && b <= c) branch(max_C)
|
||
move $v0, $s1 # if(a <= b && b > c) max = b
|
||
j done # Jump to done
|
||
|
||
max_C:
|
||
move $v0, $s2 # max = c
|
||
|
||
done: # End of program
|
||
|
||
## LOOPS ##
|
||
_loops:
|
||
# The basic structure of loops is having an exit condition and a jump
|
||
# instruction to continue its execution
|
||
li $t0, 0
|
||
while:
|
||
bgt $t0, 9, end_while # While $t0 is less than 10,
|
||
# keep iterating
|
||
#actual loop content would go here
|
||
addi $t0, $t0, 1 # Increment the value
|
||
j while # Jump back to the beginning of
|
||
# the loop
|
||
end_while:
|
||
|
||
# 2D Matrix Traversal
|
||
# Assume that $a0 stores the address of an integer matrix which is 3 x 3
|
||
li $t0, 0 # Counter for i
|
||
li $t1, 0 # Counter for j
|
||
matrix_row:
|
||
bgt $t0, 3, matrix_row_end
|
||
|
||
matrix_col:
|
||
bgt $t1, 3, matrix_col_end
|
||
|
||
# Do stuff
|
||
|
||
addi $t1, $t1, 1 # Increment the col counter
|
||
matrix_col_end:
|
||
|
||
# Do stuff
|
||
|
||
addi $t0, $t0, 1
|
||
matrix_row_end:
|
||
|
||
## FUNCTIONS ##
|
||
_functions:
|
||
# Functions are callable procedures that can accept arguments and return
|
||
# values all denoted with labels, like above
|
||
|
||
main: # Programs begin with main func
|
||
jal return_1 # jal will store the current PC in $ra
|
||
# and then jump to return_1
|
||
|
||
# What if we want to pass in args?
|
||
# First we must pass in our parameters to the argument registers
|
||
li $a0, 1
|
||
li $a1, 2
|
||
jal sum # Now we can call the function
|
||
|
||
# How about recursion?
|
||
# This is a bit more work since we need to make sure we save and restore
|
||
# the previous PC in $ra since jal will automatically overwrite
|
||
# on each call
|
||
li $a0, 3
|
||
jal fact
|
||
|
||
li $v0, 10
|
||
syscall
|
||
|
||
# This function returns 1
|
||
return_1:
|
||
li $v0, 1 # Load val in return register $v0
|
||
jr $ra # Jump back to old PC to continue exec
|
||
|
||
|
||
# Function with 2 args
|
||
sum:
|
||
add $v0, $a0, $a1
|
||
jr $ra # Return
|
||
|
||
# Recursive function to find factorial
|
||
fact:
|
||
addi $sp, $sp, -8 # Allocate space in stack
|
||
sw $s0, ($sp) # Store reg that holds current num
|
||
sw $ra, 4($sp) # Store previous PC
|
||
|
||
li $v0, 1 # Init return value
|
||
beq $a0, 0, fact_done # Finish if param is 0
|
||
|
||
# Otherwise, continue recursion
|
||
move $s0, $a0 # Copy $a0 to $s0
|
||
sub $a0, $a0, 1
|
||
jal fact
|
||
|
||
mul $v0, $s0, $v0 # Multiplication is done
|
||
|
||
fact_done:
|
||
lw $s0, ($sp)
|
||
lw $ra, 4($sp) # Restore the PC
|
||
addi $sp, $sp, 8
|
||
|
||
jr $ra
|
||
|
||
## MACROS ##
|
||
_macros:
|
||
# Macros are extremely useful for substituting repeated code blocks with a
|
||
# single label for better readability
|
||
# These are in no means substitutes for functions
|
||
# These must be declared before it is used
|
||
|
||
# Macro for printing newlines (since these can be very repetitive)
|
||
.macro println()
|
||
la $a0, newline # New line string stored here
|
||
li $v0, 4
|
||
syscall
|
||
.end_macro
|
||
|
||
println() # Assembler will copy that block of
|
||
# code here before running
|
||
|
||
# Parameters can be passed in through macros.
|
||
# These are denoted by a '%' sign with any name you choose
|
||
.macro print_int(%num)
|
||
li $v0, 1
|
||
lw $a0, %num
|
||
syscall
|
||
.end_macro
|
||
|
||
li $t0, 1
|
||
print_int($t0)
|
||
|
||
# We can also pass in immediates for macros
|
||
.macro immediates(%a, %b)
|
||
add $t0, %a, %b
|
||
.end_macro
|
||
|
||
immediates(3, 5)
|
||
|
||
# Along with passing in labels
|
||
.macro print(%string)
|
||
la $a0, %string
|
||
li $v0, 4
|
||
syscall
|
||
.end_macro
|
||
|
||
print(hello_world)
|
||
|
||
## ARRAYS ##
|
||
.data
|
||
list: .word 3, 0, 1, 2, 6 # This is an array of words
|
||
char_arr: .asciiz "hello" # This is a char array
|
||
buffer: .space 128 # Allocates a block in memory, does
|
||
# not automatically clear
|
||
# These blocks of memory are aligned
|
||
# next to each other
|
||
|
||
.text
|
||
la $s0, list # Load address of list
|
||
li $t0, 0 # Counter
|
||
li $t1, 5 # Length of the list
|
||
|
||
loop:
|
||
bge $t0, $t1, end_loop
|
||
|
||
lw $a0, ($s0)
|
||
li $v0, 1
|
||
syscall # Print the number
|
||
|
||
addi $s0, $s0, 4 # Size of a word is 4 bytes
|
||
addi $t0, $t0, 1 # Increment
|
||
j loop
|
||
end_loop:
|
||
|
||
## INCLUDE ##
|
||
# You do this to import external files into your program (behind the scenes,
|
||
# it really just takes whatever code that is in that file and places it where
|
||
# the include statement is)
|
||
.include "somefile.asm"
|
||
|
||
```
|