New Pacman for Atari 2600

New Pacman for Atari 2600
atariage.com

It's so easy to love old-school programming. (For comparison, my comment here is 178 characters.)

(See http://www.oric.org/index.php?page=software&fille=top150game...)

We got Space:1999, 1337 (Elite clone), SchoolDaze, Impossible Mission, Oricium, 4K Kong .. a lot of really awesome titles .. in the last few years. Also, new techniques have been discovered and continually refined by the core die-hards, meaning we're seeing things on the platform that we in the 80's could only ever have dreamed of seeing .. new color modes, new ways of handling animation, etc. It really is astounding to return to these platforms, 30 years later, and see new titles being pushed out by the ever-eager hackers who are keeping the platforms alive. Heck, we even got new hardware for the Oric-1/Atmos platform in the form of a dedicated disk emulation system, whose microcontroller alone, itself, is more powerful than the Oric ever was, but which nevertheless is being pressed into the disk-emulating duties that makes the Oric-1, at last complete. ;)

So if you've got an old 8-bit machine in your closet, get it out, wire it up, dust if off, and get out there on the 'net to find the elite groups keeping these systems alive. And remember: old computers never die - their users do!

An even more minimalist design where you just have one register, the next pixel to output, wouldn't work because the CPU isn't fast enough to update it: the electron beam outputs 3 pixels per CPU cycle, and of course many instructions take more than one cycle, too. Instead an auxiliary microprocessor, the TIA, is clocked 3x as fast as the main CPU and does the real-time compositing of these various registers into the one value to output.

All the details you could want are in the Stella Programmer's Guide, a 1979 guide/manual that resurfaced on the net: http://alienbill.com/2600/101/docs/stella.html

There is also an interesting book looking at a few case studies (one per chapter) of how the Atari's weird hardware influenced the design of some of its games: http://mitpress.mit.edu/books/racing-beam

In short, the TIA chip does act as video memory - but not the way we treat it today. It has various registers that you can write into to define how the next line will be drawn. eg, you create a background by writing 20 bits into the 'playfield' register. This is mirrored vertically to fill out a 40-bit wide background, and then you write in a foreground & background colour.

Similar registers exist to hold sprites for a ball, two players, and two missiles.

And then if all of this didn't seem limiting enough for you, your game (the only process running on the machine) is responsible for maintaining most the timing for the television controller itself - so you actually spend most your time managing the TIA, with only a small number of cycles at the end of each line, and a better number of cycles after the last line, but before the next screen starts drawing - in order to actually perform game logic itself.