subroutines
callers (sub or main routine)
callees (subroutine)
nested subroutines (subcalls)
end a call with RTS instruction
previous address stored in link register
old address pushed on to stack

lots of jibba jabba about making subroutines
need to restore unspecified registers to previous state, registers assigned for inputs are fair game

shift-add multiplication:
set res to 0, for each bit in num 1, shift num2 by that much and add to total
Hardcore way with no loops uses BIT.W and 8 hard coded bit masks
loops way
R4 = n1
R5 = n2
R6 = 7
R7 = temp reg
R8 = 0
mloop:	move R6,R7
	shift #1,R7

as for assignments, quick core code for multiplication
R4 = num1
R5 = num2
R6 = total
aloop: 	CMP #0,R4
	JEQ end
	DEC R4
	ADD.W R5,R6
	JMP aloop


end: ;we're done here