The cpsmidi opcode only produces meaningful results in a Midi-activated note (either real-time or from a Midi score with the -F flag). With cpsmidi, the Midi note number value is taken from the Midi event that is internally associated with the instrument instance. On the other hand, the cpsmidinn opcode may be used in any Csound instrument instance whether it is activated from a Midi event, score event, line event, or from another instrument. The input value for cpsmidinn might for example come from a p-field in a textual score or it may have been retrieved from the real-time Midi event that activated the current note using the notnum opcode.