This looks pretty clear now that if my port pointer in c code is holding a constant address(points to one register along the code) it's most likely that the compiler will choose out/in over lds/sts - that also uses immediate address but bigger than the one out/in uses - that needs less cycles and space than sts/lds , but if I make this pointer points to more than one register along the code the compiler will choose to use st/ld with an indirect address which also takes more space and cycles but it's probably the only way to compile that code.. I think that's what you mean here right?