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feat(mips.html.markdown): Added basics of loading and storing instructions

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spiderpig86 2018-06-24 14:55:47 -04:00
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@ -19,7 +19,7 @@ The MIPS (Microprocessor without Interlocked Pipeline Stages) Assembly language
.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
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)
@ -32,5 +32,34 @@ The MIPS (Microprocessor without Interlocked Pipeline Stages) Assembly language
_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 this will be executed first
# Let's print "hello world"
la $a0, hello_world # Load address of string stored in memory
li $v0, 4 # Load the syscall value (indicating type of functionality)
syscall # Perform the specified syscall with the given argument ($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
```