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That Time I By chance Deleted a Sport From MAME

That Time I By chance Deleted a Sport From MAME

2024-03-01 05:51:11

Awhile again, I had the prospect to dump a game for MAME. I informed myself that if the prospect ever got here up once more, I’d contribute once more. Fortunately, it seems I didn’t have to attend too lengthy—however the story didn’t finish like I anticipated it to.

In-game screenshot of Martial Masters

Once I purchased my PGM arcade motherboard, the #1 recreation I needed to personal was a one-on-one combating recreation known as Martial Masters. It’s a deeply underrated, attractive recreation—and judging from the value it goes for as of late, I’m not the one one after it. It took fairly a little bit of looking till I discovered a replica inside my worth vary however my regular PGM recreation seller in China lastly tracked down a replica to promote me a number of months in the past. I used to be excited to lastly play it on the unique {hardware}, but in addition to see if I had one other probability to contribute a recreation to MAME.

When it arrived, even earlier than I had the prospect to test the model quantity, I used to be stunned to see it was a Taiwanese area recreation. All of IGS’s video games have simplified Chinese language area variants on the market in China; it’s uncommon to see a standard Chinese language model from Taiwan present up over there. It may simply be an indication that the sport was so standard they introduced over additional cartridges from Taiwan when there weren’t sufficient for native arcades. As soon as I booted the sport and made observe of its model numbers, I checked MAME and noticed that there was an identical recreation in its database: martmasttw, or a particular Taiwanese model of revision 1.02. That additionally stunned me—IGS sometimes didn’t produce solely separate builds for various areas. As a substitute, every of their video games accommodates the information for each language and area in its ROMs, and the area code in its copy safety chip determines what area it boots up as.

Screenshot of Martial Masters crashing

The opposite factor I observed about MAME’s martmasttw was a remark within the supply code noting that it may be a foul dump—that’s, an invalid learn that produced corrupted information. This isn’t that unusual when dumping these types of video games. Whether or not it’s resulting from dying chips or {hardware} points with the studying course of, typically a learn simply goes mistaken and it will get missed. As soon as I booted it up in MAME, I confirmed it regarded like a foul dump. It immediately crashes with an unlawful instruction error, a transparent signal of corrupted program code. Now that I owned the sport, I had an opportunity to dump the right ROMs and repair MAME’s database.

Photo of a game chip being held

As quickly as I opened the cartridge, I observed one thing fascinating: these weren’t the chips I used to be anticipated. Like with The Gladiator, I solely wanted to take away and dump two socketed chips, however these have been a totally completely different mannequin. Different PGM video games utilizing the identical {hardware} sometimes use 27C322 (4MB) and 27C160 (2MB) chips, which have been widespread EPROMs of their time interval. Right here, although, I noticed one thing far more unique: an OKI 27C3202 soldered right into a customized adapter. The sport board itself is actually the identical one which’s in The Gladiator, so it was clear that the adapter was presenting them as 4MB 27C322 chips.

I haven’t been in a position to determine why it was designed this fashion. It may well’t have been low-cost to design and manufacture these customized adapters, and different PGM video games that have been made each earlier than and after this one all use the extra widespread chips with none adapters. I’ve solely seen a single different recreation constructed this fashion. Was there a 27C322 scarcity on the time this particular recreation was being made? Had been they experimenting with new designs and ended up abandoning this method? It’s laborious to inform.

Photo of a game chip being dumped in an EPROM reader

I solely have an EPROM reader adapter for chips within the 27C322 household, so I hoped it might would be capable to deal with studying them simply positive. On my first try, it rejected it; so far as I can inform, it was attempting to carry out “sensible” verification of the chip, which failed for the reason that underlying chip beneath IGS’s adapter isn’t truly the chip it’s attempting to question. I finally tricked it by inserting an actual 27C322 first and studying that earlier than swapping over to the chip I truly needed to learn. As soon as the reader’s acknowledged a minimum of one chip, it appears comfortable to stay in 27C322 mode persistently.

My first learn appeared positive, and the dumped information did have a unique hash from what MAME acknowledged. Success! …or so I believed, till I attempted truly booting the sport, the place it crashed once more. I went again to the EPROM reader to ensure the chip was seated accurately earlier than doing a brand new take a look at learn. From the bodily design of the adapters, I knew that getting it seated may be a problem.

The reader makes use of a ZIF socket which normally makes it simple to insert and take away chips. This time, although, there was an fascinating complication. Due to the way it’s constructed, the socket has a “lip” on the finish previous the ultimate set of pins. With a standard 27C322, that’s not an issue; the chip ends proper on the ultimate set of pins, so nothing hangs over the top of the chip. This adapter has a really completely different form from an actual 27C322 chip, nevertheless—there’s a dangling “head” that accommodates the precise chip, as seen within the photograph above exhibiting the underside of the adapter. On the actual board it hangs harmlessly over the top of the socket, however on a ZIF socket it finally ends up truly making contact with the top of the socket and retains the pins from with the ability to sit as deeply as it might regular sit. I haven’t spoken to the one that initially dumped this revision, however I think that that is the difficulty behind the unhealthy dump.

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I ended up holding the apdater with one hand to stabilize it and maintain all the pins as at the same time as I may whereas I locked the ZIF socket’s lever a second time; this time, it appeared as if I’d been in a position to get it sitting as at the same time as attainable. I then carried out a number of extra reads and, earlier than attempting in addition it once more, in contrast them in opposition to one another. This time, I noticed that these new reads have been completely different from the primary try—and that they have been byte-for-byte similar to one another.

Screenshot of Martial Masters's title screen

As soon as I had what appeared like good dump of each chips, I booted them up in MAME to see if it might work. Not like MAME’s ROMs, it booted instantly with out points and labored completely. After I performed a number of rounds with out a single crash or sudden behaviour, I used to be happy that my new dumps have been positive. As I used to be on the brink of submit a pull request to MAME to replace the hashes in its database, nevertheless, I occurred to grep the supply for them and observed one thing humorous—they have been already there. In one other model of Martial Masters.

I discussed earlier that I used to be stunned that MAME had labelled the Taiwanese 1.02 model of Martial Masters as a separate revision from the Chinese language 1.02. Properly, because it seems, as soon as the ROMs are dumped accurately it’s not a separate revision. The ROMs are literally byte-for-byte similar; it’s solely the unhealthy dump that had made MAME contemplate martmasttw a separate revision this entire time.

That is the purpose the place I’d supposed to open a pull request to MAME simply updating a number of hashes for the right dump, however with every little thing I’d discovered the final pull request deleted martmasttw solely. I had got down to repair a revision of the sport in MAME, and make yet one more verison of it playable. As a substitute, I’d confirmed it didn’t exist within the first place. This wasn’t the place I anticipated to finish up, however it does educate an necessary lesson: corrupted information can go unnoticed for years if it’s not double and triple checked.

And, greater than that, it’s a reminder that databases are an everlasting work in progress. MAME’s checklist of ROMs can be as shut as there may be to a worldwide catalogue of arcade video games and their revisions, however it’s nonetheless fallible. Databases develop and, typically, they shrink; proving a piece doesn’t exist might be simply as necessary as uncovering new works.

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