@pwillard - I've been building systems for years & ALWAYS use a protocol based on checksum, never count on the data being sent, even over a short distance to remain intact. I've built systems that have had inter chip communication that just send basic data, and they have failed to pass the correct bit stream. To do things the correct way is NOT a 'because you can' thing, it's a 'if you are going to do it, do it right' thing.
I've never had a house fire, or been mugged or had any crime committed against ME, so The Fire department and Police forces should be disbanded based on your premise.
My question is, what would be the best protocol to send data from Arduino to Raspberry and vice versa.
Distance between them would be only a few centimeters so this shouldn't be a problem.
We were answering the question posed by luxy.