Citoplazma

Citoplazma is the latest demo from the Demodogs (also known as Demopsi) crew! My role for this production was handling the coding, directing the flow, and gluing the whole thing together.

I whipped this demo up from absolute scratch in just 5 days of intense work. I know it’s not some mind-blowing, groundbreaking masterpiece, but I hope you guys enjoy it!

We put it together specifically for Forever C—the legendary 8-bit multiscene demoparty. The very first time Citoplazma was ever run on real Atari hardware was right there live at the party. Because I only own a stock Atari 800XL with no memory expansions, I literally couldn’t test the full production on real silicon myself beforehand. As usually happens when you rely entirely on emulators, a few hardware bugs and compatibility issues reared their heads during the live screening, so I’m currently working hard to patch those up!

At the party, the demo was actually screened on an Atari outfitted with a 256KB memory expansion. However, you don’t need that much beef to run it—a standard Atari 130XE (128KB) is all it takes. Just keep in mind that the soundtrack was composed in stereo, so if you run it on a machine without a second POKEY chip mod, the music is going to sound pretty weird (though the demo will still run fine!).

The Live Bug Breakdown

The glitch that wrecked our live presentation happened right at the transition point where the fullscreen picture of the girl switches over to the screen with the blue scroll text. Exactly at that frame, the player routine completely lost its mind and started spitting out nasty, garbled noise.

To fix it, I jumped under the hood and made two key adjustments:

Extended Memory Allocation: I cleaned up how the code maps and cycles through the extra 64KB banks to prevent memory overlapping.
NMI Vector Fix: I tracked down and fixed a rogue NMI (Non-Maskable Interrupt) vector switch that was improperly hijacking the CPU timing during the screen transition and throwing the POKEY update cycle out of whack.

Hopefully, everything runs smooth as butter now!