Pre Lecture Video Notes

An instruction is a command that hardware understands

• Instruction set is the vocabulary of commands understood by a given computer
• Included arithmetic instructions, memory access instructions, logical operations, instructions for making decisions

The general classes of MIPS instructions are

• Arithmetic
  • add, subtract, multiply, divide
• Logical
  • and, or, not, not shift
• Data transfer
  • load from or store to memory
• Transfer control
  • Jumps, branches, calls, returns

Arithmetic Instructions

• Each MIPS only performs on operation
• Each one must have 3 variables
• These variables can be the same

add a, b, c     # a = b + c;
add a, a, a.    # a = a + a

sub a, b, a   # f contains t0 - t1

# a = b - ((b+c) + a + a) 

• if the statement is more complex we need to break it into pieces

In MIPS, operands for general arithmetic operations must be from registers of constants

• 32 programmer useable registers
• Reflects "Faster is better" Registers use less power

Name	Number	Use
$zero	0	Const 0
$at	1	Assembler temporary, for resolving pseudoinstructions
$v0 - $v1	2-3	Function results and expression evaluation
$a0 - $a3	4-7	Arguments
$t0 - $t9	8-15, 24-25	Temporary
$s0 - $s7	16-23	Saved Temporary
$k0 - $k1	26-27	OS Kernel
$gp	28	Global pointer
$sp	29	Stack pointer
$fp	30	Frame pointer
$ra	31	Return address

More about how these work: [[Intro To MIPS]] More about the use of these: [[Logical Operations]]

The general form for a mips instruction is

Instruction_mnemonic $target, $source1, $source2

• MIPS is case insensitive (not case sensitive) so Add can be ADD or even aDd

We don’t have variables, we have registers.