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Centipede TB released! (2600)


Arenafoot

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As a personal request from myself back in January of this year in a "hack" forum (on the other website), the Atari 2600 verison of Centipede has been hacked to work with an Atari CX-22 trak-ball!!

 

It is only in NTSC and only works with the CX-22 trak-ball and NOT with the CX-80 trak-ball.

 

Hack made possible by Thomas Jentzsch & Omegamatrix. Here's the details:

 

Success! At least for some of you. icon_wink.gif

Attached you find a trackball version of Centipede. This only works for the CX-22.

Please do not expect a CX-80 (or Amiga mouse) version soon. The encoding of the CX-22 is different from the CX-80 and this difference (especially the isolated direction bits) allows some shortcuts which juuust made this hack possible.

 

Someone should test this hack on real hardware, because I don't own a CX-22.

Some history:
The Centipede kernel is pretty busy, but finding 20..25 cycles was no major problem. Also freeing up some ROM was not that difficult. The biggest problem was to find enough free RAM because Centipede uses almost every bit of every byte available. The first byte was easy, because that was used for faster x-movement in the old joystick code. Originally I thought I would need three more RAM bytes, but I only found one more which could be used without major impact (game variation selection doesn't work in demo mode anymore). 

 

Yesterday, Omegamatrix provided an idea how so save one byte by sharing the last tracking value in one variable. Since I found no third RAM byte, I today decided to share the movement counters for X and Y direction. Since they only have 4 bit each now, they may overrun when you move very fast. and affect each other. But I doubt that will happen a lot.

 

As of now the code tracks both directions in every 9th scan line during the by far most utilized kernel. There are two other kernels, but those are executed only once or twice per frame. If you find the controls not responsive enough, I can try to add the trackball code into those kernels too.

BTW: I have reduced the vertical gun speed by 50%, because IMO that works better. Let me know if you find it too slow.

 

 

All of the responses I've seen say it works great and no problems with the firing also.

Enjoy!

Centipede CX-22 Hack (NTSC) v1.0.bin

Brian Matherne - owner/curator of "The MOST comprehensive list of Atari VCS/2600 homebrews ever compiled." http://tiny.cc/Atari2600Homebrew

author of "The Atari 2600 Homebrew Companion" book series available on Amazon! www.amazon.com/author/brianmatherne

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and possibly Reactor, Crystal Castles, & Millipede trak-ball versions in the near future too!?!?!?!?!

Brian Matherne - owner/curator of "The MOST comprehensive list of Atari VCS/2600 homebrews ever compiled." http://tiny.cc/Atari2600Homebrew

author of "The Atari 2600 Homebrew Companion" book series available on Amazon! www.amazon.com/author/brianmatherne

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Thomas Jentzsch Is a retrogaming treasure.

I agree!

Brian Matherne - owner/curator of "The MOST comprehensive list of Atari VCS/2600 homebrews ever compiled." http://tiny.cc/Atari2600Homebrew

author of "The Atari 2600 Homebrew Companion" book series available on Amazon! www.amazon.com/author/brianmatherne

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Brian Matherne - owner/curator of "The MOST comprehensive list of Atari VCS/2600 homebrews ever compiled." http://tiny.cc/Atari2600Homebrew

author of "The Atari 2600 Homebrew Companion" book series available on Amazon! www.amazon.com/author/brianmatherne

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Brian Matherne - owner/curator of "The MOST comprehensive list of Atari VCS/2600 homebrews ever compiled." http://tiny.cc/Atari2600Homebrew

author of "The Atari 2600 Homebrew Companion" book series available on Amazon! www.amazon.com/author/brianmatherne

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Atari's engineer Dan Kramer trak-ball ad.......... 

 

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Brian Matherne - owner/curator of "The MOST comprehensive list of Atari VCS/2600 homebrews ever compiled." http://tiny.cc/Atari2600Homebrew

author of "The Atari 2600 Homebrew Companion" book series available on Amazon! www.amazon.com/author/brianmatherne

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