1. Digital signal processing apparatus comprising a plurality of available hardware resource means and a first instruction set means having access to said available hardware resource means, so that at least a part of said hardware resource means execute operations under control of said first instruction set means; characterized by a second instruction set means having access to only a predetermined limited subset of said plurality of available hardware resource means, so that at least a part of said predetermined limited subset of said hardware resource means execute operations under control of said second instruction set means.