shift add, see last class notes

hardware multiplier stuff
write op1
specify type of op, signed, unsigned, (optionally accumulate)
write op2 (triggers operation)
read result

lower section always contains lower 16 bits of result
upper section contains
mpy	upper 16 bits
mpys	sign
mac	upper 16 its
macs	upper 16 bits, 2's comp

sumext registers
mpy	0
mpys	extd sign
mac	carry
macs	sign

jibbering about stack frames and how they're used to store local variables
on the msp430, stack access is just as fast as memory access
this is not so for bigger machines with external memory