Wed. Nov 30th, 2022
A look at the circuit of a
enlarge / A look inside the circuit of a “discovered” arcade chip.

The community behind the Multiple Arcade Machine Emulator (MAME) has gone to great lengths to preserve thousands of arcade games on hundreds of different chipsets through emulation over the years. That conservation effort has now grown into physically opening DRM-protected chips to view the raw code written inside them — and it’s an effort that could use your help through crowdsourcing.

While dumping the raw code from many arcade chips is a simple process, many titles are un-dumped and not emulated due to the digital rights management code that prevents the ROM files from being easily copied from the base chips with integrated circuits. For some of those protected chips, the decapping process can be used as a DRM solution by literally removing the “cap” from the chip with nitric acid and acetone.

Now that the underlying circuit paths in the chip are visible, there are a few possible ways to get to the raw code. For some chips, a little quick soldering to that exposed circuit can create a dumped file that can bypass any DRM further down the line. However, in the case of chips that use a non-rewritable Mask ROM, the decappers can look through a microscope (or high-resolution scan) to to see the raw zeros and ones that make up the otherwise protected ROM code.

Come together, now, over chips

At 100x magnification, you can see the individual bits and bytes that make up the raw code in this Mask ROM.
enlarge / At 100x magnification, you can see the individual bits and bytes that make up the raw code in this Mask ROM.

Decapping is a time consuming and expensive process, but the MAME development community has shown a willingness to put effort and money into it. A crowdfunded MAME discovery attempt from years ago led to the dumping of key chips found in games such as Bubble Bobble, Galaga, Arkanoid, Street Fighter EX, and dozens of others. However, in 2015, that effort had failed due to allegations that a key member of the internet had disappeared and essentially ran off with dozens of rare chips in his possession.

Since then, the Caps0ff project has taken on the MAME decapping mantle, raising money to acquire and decapitate hundreds of undumped chips in various states of disrepair. The project has already provided detailed breakdowns of its efforts to remove chips from games such as bad guys, Mortal Kombat 4and some cult classics from developer Toaplan, among others.

An example of the interface used to crowdsource the ROM transcript of a decapped Fujitsu chip.

An example of the interface used to crowdsource the ROM transcript of a decapped Fujitsu chip.

For a set of Fujitsu-made chips used in Sega’s Virtua Racing, but Caps0ff had to seek help through crowdsourcing. With previously used computer vision algorithms apparently unable to extract reliable data from these exposed Mask ROMs, the team set up a tool that allows human eyes (and brains) to do the visual decoding themselves. That tool asks users to essentially transcribe 1s and 0s from black-and-white photos of an ultra-zoomed portion of the chip, covered with a guidance grid to help determine where one bit ends and the next begins.

The first chip from that set was successfully transcribed by 88 volunteers in about 15 hours this week, according to MAMEWorld poster Drawcifer. That tool will be improved to make future chip transcriptions even more efficient – keep an eye on the Caps0ff blog if you want to contribute in the future.

The reveal is reminiscent of the Apple II preservation scene, which went to great lengths to crack and copy decades-old games and programs written for the monochrome computer of the 1980s. The lesson here may be that, with enough time and attention, there probably isn’t a DRM schedule that can’t be broken by a devoted group of historically minded fans.

By akfire1

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