Desmume (NDS) - How does "quick switch" screen mode work?

I can’t figure out how this setting works or how to switch screens with it active. Can anybody tell me what it does, exactly, and how to use it?

When you select that mode, whatever you have mapped as R3 will switch between the screens.

I show it working on my Gam3B0x here:

As Awakened said though, you just map the feature to a controller, and then it switches between top and bottom screens at the touch of a button.

Thanks for the info, guys. It’s working fine for me.