It’s a bit ironic that an Atari 2600 game based on Raiders of the Lost Ark — a movie about archaeology — is now the subject of its own archaeological expedition as [Dennis Debro] and [Halkun] spent time reverse-engineering the game. Luckily, they shared their findings, so you can enjoy it the same way you can visit a king’s tomb without having to discover it and dig for it. If you don’t remember the game, you might enjoy the demo from [Speedy Walkthroughs] in the video below.
If you are only used to modern software, you might think this is little more than someone dumping the program code and commenting it. However, on these old, limited systems, you have to really understand the actual architecture because there are so many things you have to manage that are specific to the hardware.
For example, the game has two 4K ROM banks that use a strange switching mechanism. The entire game is built around the NTSC television signal. Everything is oriented toward generating the 60 Hz frame rate. Game logic runs during the vertical blanking and over-scan sections to prevent strange visible artifacts due to software running.
This is a fascinating look inside game coding as it existed around 1982. Of course, you can also run everything using emulation. Usually, our reverse engineering is more hardware-related. But we do love these old games, too.
Writing games back then was more like being a modern firmware engineer than a modern software engineer.
Writing for Atari 2600 was even harder. You had to draw video in real time because there was no video RAM to store image. You had to count every cycle to be sure you triggered vertical and horizontal blanking at the right time. Too short or too long a code between blanking can lead to tearing or rolling image back in the day (and would result in no signal on modern display due to incompatible timing)
I created a simple demo for 2600 ages ago, it was rather hard to get it right. never tried 2600 programming since then.
“Racing the beam”
While it sounds complicated, shortly before the Atari you had to be designing logic for a Pong chip and the like in order to be in the electronic game industry.
Writing some 6502 assembly to poke hardware according to timing diagrams sounds downright luxurious. You could try something new out in an evening if you had UV erasable PROM or a ROM emulator (perhaps 8K SRAM?).
This will be great for anyone that wants to mod the original game for improvements. And it really could use a lot of improvements.