Inside the Homebrew Atari 2600 Scene

angryflute writes "'Have you played Atari today?' was an ad jingle for the Atari 2600 VCS game console during its reign in the early years of the video game industry, from the late 1970s to early 1980s. That question that could apply even now, according to an O'Reilly Network article, thanks to the passion of programmers who've continued to make new Atari 2600 games for the past few years."

Comments

Good Article!

[Bender_]

Good Article, seems to be quite accurate on details. And yes, I did actually read it.

I also made some attempts on vcs2600 programming some years ago. It could not be any more different from your daily C/php/... hacking. Think of microcontroller programming with even more demanding timing.

The machine has 128bytes (yes, bytes) of ram and 4-6kb of ROM. No video ram, everything is generated on the fly. The CPU does not support interrupts, all the timing is done by active waiting.

Re:Good Article!

[JanneM]

Note that you have 4k of ROM, that in addition can be bank-switched. "All" you need the RAM for is for changing variables, really. Not that it's not a pretty demanding limit (seeing how apparently the 6502 stack needs to fit as well), but you do have a bit more margin to play with that it seems at first. Most microcontrollers today look similar, with what seems like a ridiculously low amount of RAM compared to ROM.

Compare to the Commodore VIC20 - precursor to the C64 (and a wonderful machine in many ways). You had 5k total, of which 1.5k went for the video buffer. That left you with about the same amount of total codespace to play with, and there were no shortage of really good games for that machine either. The defining limitation of the 2600 really seems to be the lack of a framebuffer far more than the low amount of RAM.

Damn it

[Anonymous Coward]

I've already moderated some posts here, so I have to post as AC from another machine (or else my moderations are removed)

I've been coding some stuff on the Atari and it's an extremly cool machine.
You can actually build one yourself, if you have a little knowledge in electronics.

Most of my coding is done in the Atari 2600 emulator called "Stella":
http://freshmeat.net/projects/stella/

Worth a try if you love the 6502 and minimalism

I've done this!

[pngwen]

Of course my rom just flashes random colors and a line that remains constant going back and forth. Considering what the atari 2600 environment is like, I'm damn proud of this. It's not exactly like other architectures. Even if you are used to programming in assembly for embedded devices with tight memory constraints, the VCS is STILL a major wakeup call.

Here are some of the challenges that you will encounter:

• There is no interrupt vector system. System functions are accomplished by means of the stella chip, which looks like a section in RAM. writing and/or reading from certain memory locations triggers events (such as drawing to the screen and such)
• TIMING is YOUR responsibility! You have to count clock cycles while you program, and you have to write the code to redraw your screen scan line by scanline on each electron beam pass of the TV.
• Computation has to be performed mostly during the blanking and return phases of the electron beam. You know you have 72 clock cycles in which to operate your game logic before you have to begin drawing the screen again
• Once your program's timing gets off, you get something that looks nothing like what you intended. My moving line example had a line that stair stepped as it moved. It wasn't until I added a sufficient amount of NOPs that it lined back up.

All in all though, it is a rather ingenious system. Considering when it was made, and the maximum cost of each unit, I'd say kudos to those engineers! I hope to do some more meaningful stuff with it once I have more time. I've plans to hack hardware for it as well!

-Bob