[stella] Extra Buttony Goodness

[bob.montgomery at thomson.com]

Hi All,

After seeing some weirdness w/ Thrust+, which I eventually traced
to the Genesis 3-button gamepad I was trying to use,
I realized that there might be a way to read those extra buttons.

After some poking around; digging up schematics and talking with Thomas,
it looks like you can read the C-button on a Genesis gamepad the same
way
that you read the "Thrust" button on an Omega booster grip, except that
that value is reversed - it returns a 0 when C is pressed.

Looking at pinouts for the SMS 2-button gamepad
(http://users.erols.com/tiltonj/games/tech/smscont.html)
it looks like those would work the same way, though I have
no way to confirm this.  I have tested that, in Thrust+ at least,
when using a Genesis controller, it behaves as if the "Fire" button
of the Booster grip is always pressed (see the pinout) and the "Thrust"
button (mapped to "C") is reversed - pressing C cuts thrust, releasing
it thrusts.

I don't know if this has been noticed/mentioned before, but it seems
pretty cool to me - Genny gamepads are common as dirt, so I'd
be reasonably comfortable writing a 2600 game that took advantage
of and/or required the extra button.

And, actually, if there was some way to turn off the +5V to the
controller,
I *think* you could read the other buttons (A and Start) on the pad.

Thoughts?

-bob