Exploring Glitches: Bugs in Dreamcast Tomb Raider Chronicles and The Last Revelation

[CrisMod]

Hello everyone, after several weeks of testing to get the right settings for launching my game library with my IDE/SATA-modified Dreamshell Dreamcast, I stumbled upon two titles that hold a special place in my heart from my childhood, having known Tomb Raider from its earliest chapters.

In brief, let me explain the bugs or glitches that affect these two Dreamcast titles. After spending weeks debugging the console with my Raspberry Pi, consulting the "ISO Loader 0.8.x Beta" section on dc-swat.ru, and discussing the issue with other users regarding "Tomb Raider Chronicles," I discovered that this game freezes after about 10 minutes of gameplay or if you use the "Look" button (L button) multiple times, or if you press the "START" button to access the in-game menu. These freezes occurred randomly without a clear pattern and didn't always replicate at the same point. Some suggested it might be a problem with the modification, but the modification shouldn't cause issues with just 1 or 2 titles. Besides, the modification worked flawlessly with everything else, so I tried various images (debugging) created by different users from different regions. I experimented with all the ISOLoader settings and even tried the original physical games, but they all presented the same problem.

Until yesterday, when my modems for my 3 Dreamcasts arrived, and an unexpected result emerged. It's worth noting that I'm not sure how the developers of the Tomb Raider series associated it with the Dreamcast Modem/BBA (Broadband Adapter), but the game "Tomb Raider Chronicles" no longer has in-game freezes (tested for over 4 hours). As for "Tomb Raider: The Last Revelation," it fixed some issues with pixel rendering in certain parts of the game resulting in white/purple/gray pixels. Regarding "Tomb Raider Chronicles," it has problems with in-game freezes without a modem/BBA, so you can only play it if you have the modem (this also applies to the physical game).

In disbelief, I tried to delve deeper into this issue with some internet research, and indeed, I found a few posts that casually mentioned this problem. The two reference sites are here: `https://github.com/p1pkin/demul/issues/479` and
here: `https://www.tombraiderforums.com/showthread.php?t=155377`.

This makes sense because those involved in their significant work of providing the community with their lists of settings to make games work with the best Dreamshell/ISOLoader settings test them with modems. Thus, they couldn't have noticed this defect for those who don't have a modem. This issue occurs with all three scenarios: Dummy Modem Semi-Real (with the card inside but without the circuitry), Dummy Modem Full Plastic, and removing the modem, leaving the Dreamcast with no accessories attached.

Now, to explain and show the glitch that occurred in "Tomb Raider: The Last Revelation," I can no longer replicate it because, since I attached the real modem, it fixed the minor color pixel issues that were not visible on certain objects. Even detaching or attaching the Dummy Modem doesn't affect the game anymore because the "FIX" must have stayed in memory. I will try to replicate it again later, and if I have the images, I will post them here (I believe I will need to reset the console by removing the battery, etc.).

However, "Tomb Raider Chronicles" is replicable even with Emulators, and from my side at least with my model, which is the Dreamcast with Motherboard VA0 (the other revisions should also be included unless the circuitry of the new revisions at that time SEGA improved something in the interface where they knew it could create such a problem in a special circumstance).

I posted this post here and on DC-SWAT Forum as well, with the wish that this information will help other users.

[Wombat]

After reading your post, the part of the bugs not appearing when having a modem triggered me. As in, I have read about a similar problem in the past. I did some digging and found the article in question;

"Byrd knew that the modem was connected to the G2 bus – as was the Yamaha AICA sound chip. The sound chip had a MIDI input pin which, on the Japanese model, was tied to ground. On the North American model, the pin in question was left 'floating', and it turned out that this was what was causing the system to crash."
(source: The Untold Story Of The Bug That Almost Sank The Dreamcast's North American Launch)

Perhaps this is something worth looking into with your quest

[CrisMod]

After reading your post, the part of the bugs not appearing when having a modem triggered me. As in, I have read about a similar problem in the past. I did some digging and found the article in question;

"Byrd knew that the modem was connected to the G2 bus – as was the Yamaha AICA sound chip. The sound chip had a MIDI input pin which, on the Japanese model, was tied to ground. On the North American model, the pin in question was left 'floating', and it turned out that this was what was causing the system to crash."
(source: The Untold Story Of The Bug That Almost Sank The Dreamcast's North American Launch)

Perhaps this is something worth looking into with your quest

Thank you for your response! After reading the article, It's interesting to hear about the modem's connection to the G2 bus and its relationship with the Yamaha AICA sound chip. The fact that the sound chip had a MIDI input pin tied to ground in the Japanese model but left 'floating' in the North American model is quite intriguing.

I suspected inside my self, might be related to the audio circuitry or the pinout of some of the ground pins, which could potentially cause issues if not properly interfaced with G2 interface. I've often wondered why pressing the 'START' button in-game, which should trigger a sound in Menu opening, leads to a freeze. But in another side, I 'm not sure it's why additionally, the issues with the 'L' trigger or certain in-game camera angles causing freezes, when there's no modem attached, raise even more questions. But the article said that it's causing those freeze "..thermal noise in the room to the height of the sun or the position of the moon, according to Byrd.." .