Stand Back - Prince

[Royfan]

Hey - as most people know Prince played the great synth intro to Stand Back..

What I'm not sure of, from reading accounts of that session, is what state the song was in
before Prince played?

Was there a chord progression and melody? Or did Stevie use Prince's synth as the basis of the song, and then sing her own tune and words on it?

2 very different things
in 1 case Prince is doing a great intro..
in the other, Prince really wrote the chords to the song..

So I'm interested..