Registers

MIPS has 32 general purpose registers
In assemply, they can be referred to as their name: $a 0,$ t1 etc. or their number $0,$ 1

Name	Number	Usage
`zero`	0	Constant value 0
`v0 - v1`	2 - 3	Values for results and expression evaluation
`a0 - a3`	4 - 7	Arguments
`t0 - t7`	8 - 15	Temporaries
`s0 - s7`	16 -23	Program Variables
`t8 - t9`	24 - 25	Temporaries
`gp`	28	Global Pointer (dont modify)
`sp`	29	Stack Pointer (dont modify)
`fp`	30	Frame Pointer (dont modify)
`ra`	31	Return Address (dont modify)
`at`	1	Reserved: for assembler
`k0 - k1`	26 - 27	Reserved: for operating system

MIPS Instruction

add $s0, $s1, $s2

addi $s0, $s0, 5

The constant (in this case 5) ranges from $- 2^{15}$ to $2^{15} - 1$ because it is represented as 16-bit 2s complement

Memory is a array of memory locations
- MIPS uses byte addresses, i.e. each memory address is 1 byte (8 bits)
- MIPS addresses are 32 bits long
- Byte addressable memory: each element in the array is 1 byte (8 bits) long
- Word addressable memory: each element in the array is 1 word (32 bits for mips) long
Word alignment
- If a word data value is word aligned in memory, its address is a multiple of the word size
Accessing
- Load word lw $t0, 4($s0), Store word sw $t0, 4($s0)
  - $s0 register contains the memory address to load from (base address)
  - 4 is the offset from the address contained by $s0
  - for lw and sw , base address + offset has to be multiple of 4
- Load byte, store byte
  - Only loads and stores the lowest byte

Branch beq $s0, $s1, Label and bne $s0, $s1, Label
Greater or less than?
- Set on less than slt $t0, $s1, $s2 or slti : if $s1 < $s2 then set $t0 to 1 , else 0
- bne $t0, $zero, Label