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martyb writes:

Back before computers (and cell phones!) regularly sported multi-GHz processors and GBs of memory, there was the 6502 microprocessor. It was the CPU that powered computers made by Apple, Acorn, Atari, BBC Micro, Commodore, and others. Though the 6502 was introduced in 1975, it is far from being a dead parrot!

Classic 8-Bit Computing The Atari Way:

In the classic gaming world, even before the NES arrived on the scene, there was no name more ubiquitous than Atari. Their famous 2600 console sold almost as many units as the Nintendo 64, but was released nearly 20 years prior. In many ways, despite making mistakes that led to the video game crash of the early 80s, Atari was the first to make a path in the video game industry. If you want to explore what the era of 8-bit computing was like in the Atari age, a new resource is compiling all kinds of Atari-based projects.

To get started, this Atari Projects page has instructions on how to install Altirra (a 6502 emulator) to your PC. That is really handy if you don't happen to have a 40-year old computer lying around. Read on for lots more!

Altirra was programmed by Avery Lee to emulate the Atari 400, 800, XL, and XE computers as well as the XEGS game system. It was first released in 2009 and has been consistently updated since. Version 3.0 was released in December of 2017. According to the website, "Altirra is designed with emulation quality in mind, sometimes over speed and polish. It's designed as a system emulator and debugger instead of a games machine, so there is some setup involved". Altirra is licensed under the GNU General Public License (GPL), version 2.

From there, go back to Atari Projects for some code to run on it. Also available on that site are links to still other sites which have downloadable Atari programs.

Then, for those who are curious about the 6502 processor itself, take a look at Visual Transistor-level Simulation of the 6502 CPU. There you can find an emulator of the 6502 processor that runs in your browser! It depicts all activity on the chip when each instruction is executed. Starting from high-resolution photographs of the silicon die and its substrate, they created an exact model of its circuits. They state:

This model is very accurate and can run classic 6502 programs, including Atari games. By rendering our polygons with colors corresponding to their 'high' or 'low' logic state, we can show, visually, exactly how the chip operates: how it reads data and instructions from memory, how its registers and internal busses operate, and how toggling a single input pin (the 'clock') on and off drives the entire chip to step through a program and get things done.

Now you can really say "I see what you did there."

If that's whetted your appetite, check out http://www.6502.org/ for lots more.

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