This is emulation, so hardware rules, not MODEL OF JOYSTICK rules...
Two buttons for joystick. My "Amiga hardware reference manual" book is aprox at 1000km of my current home. I don't google for Amiga... these times we must read books! ;-)
I don't remember neither memory-mapped ports neither reading protocols (the only memory-mapped IO I can remember is $dff180=background color), but it's a fact.