Catching up part 2: Fish ‘n’ FlashChip

Have you heard of Fish Life? Honestly if you end up reading this article, you have probably already read all the other websites related to the Dreamcast, from the most well known to those dead for decades, desperately seeking for any kind of content as long it doesn’t appear in your browser history…. Seems like you and I would surely get along 🙂

Fish Life is a set of fish tank simulators developed by SEGA in 2000. Several editions were made, each featuring a different part of the sea life. While some may challenge the fish simulation market SEGA tried to penetrate, Fish Life definitely pushed a little bit forward the Dreamcast capabilities.

Before going any further, I would like to thank Laurent C. for sharing the Fish Life GDI dump. Having early access to the game/app gave me the opportunity to patch it so that it runs on basically any Dreamcast.

First of all, the hardware. Fish Life was made to run on a specific revision of the Dreamcast, HKS-0300, that comes in a DVD reader enclosure along with a SEGA branded touch screen, HKS-0100. A touch screen you said? It seems like indeed that it is possible on the Dreamcast and I will detail this point later.

Fish Life unit with its touch screen (source)

From the few pictures available, you can easily tell that SEGA kept the retail Dreamcast hardware almost untouched, just change the way the GDROM tray opens, squeezed a controller board inside and mapped its controls to external buttons at the back of the case. A closer look gives you some hints on the touch screen functionality: there are a couple of wires from the motherboard that are connected to a serial port.

Inside the Fish Life unit (source)
Please check out the source, Musée Bolo took many pictures!

The Hitachi SH4 processor offers a serial interface you have probably used to link your system to another Dreamcast, a Neogeo Pocket or to a serial SD card adapter. Well there is more. The processor actually has two serial interfaces and the Fish Life unit uses the second one, not used on retail Dreamcasts, to receive touch packets from the screen. The packet format has already been reversed engineered (thanks to MetalliC) and even though I haven’t tested it myself, I wouldn’t be surprised if any serial touch screen would work out of the box.

The other main hardware specificity is not noticeable on the picture. When Laurent C. sent me the GDI files, he also provided the bios and the flash memory dumps. The bios is just the regular bootROM v1.01d. The flash memory however is different. First it is not 128Kb long but 256Kb, divided into two identical 128Kb halves (so one is just mirrored). Was the 128Kb chip getting old? Was the 256Kb flash chip cheaper? That is what I think but so far I have no information to back this up.

Anyway, it is now time to talk about the software. As I said earlier, the game supports the touch screen. It means that with the touch screen connected, if you put your finger on the screen the fish will, depending on their mood, follow it. All the routines to receive the « touch packets » from the screen are in the program file. So with a little bit of work (if not already done) it would be possible to recreate the touch mechanism and port it to KOS for future use in homebrew. Isn’t that cool!? Additionally to that, the game supports the mic so that you can interact with the fish. It seems that the voice recognition has a japanese and also an english word dictionary so that you don’t have to bother learning japanese to tell the fish to eat. And by the way « to eat » is « taberu » in japanese and if you have the feeling the fish are a little bit deaf when you say it in japanese it’s probably due to your accent… Sorry to say so but they are a bit picky 😉

« Great, but can I play the game now? »

When I first put my hands on it, I tried to load it up on my GDEMU. The game refused to boot (hanged on the license screen). I disassembled the binary and found out that the game, early in its execution, reads the flash memory, which it is not very common, at least for licensed games. The code revealed that the game actually checks that the machine name/code stored in the flash is correct. And correct on retail Dreamcast would be the string « Dreamcast » located at two different places in the read-only partition #0 of the flash memory. But here, we have a special hardware thus a special machine name: « Fish Life ».

Flash partition #0 from a retail Dreamcast
Flash partition #0 from a Fish Life unit

A quick patch that bypass this check was enough to make the GDI image to boot on any Dreamcast.

The function that checks the machine code. If “0x30FF” at 0x8c000070 if not found, it sets “usrMainMenuAction” to “0x09” which later on makes the code loop forever.

By the way, the patch and the patched GDI image are available at the end of this article.

« Why can’t I create a Fish Life CDI image? »

Having a working GDI image is nice but not enough to have working CDI image. It’s where comes the last feature I wanted to talk about. In the Katana SDK, there is the IPMaker tool that was used to create the boot program, injected in the ISO9660 boot sectors. With this tool developers could set meta informations (game name, region, VGA flag, etc.) and also activate some feature such as the playlog. As its name suggests, it activates a log that contains the current time, the game actually booting and other information. The log is then stored in a the flash memory. I think SEGA didn’t have enough time to deploy this feature, very similar to what you can find in newer system. Anyway, when the game code boots it ensures that the playlog contains an entry for Fish Life (based on the product number found in the boot sector). Why? If you look at the Fish Life unit, there is no VMU port accessible and the game has a settings menu. Guess what? It stores the settings in the log, in the last entry found. I haven’t had the chance yet to investigate why the boot sector has to create the entry but I think it works like a session where booting the game creates it so that the game code can store the settings later on. And usually when you create a CDI image, you re-use a working boot sector or create one from non official tools that do not having the playlog library embedded: the game starts, cannot find the game playlog and finally displays an error screen. Several workarounds exist but I won’t mention them here as this article is already longer then expected 😉

Download:

Patch: jc-fishlife-flashchk-patch-v1.0.zip

Patched GDI Image: Fish Life Amazon (2000)(SEGA)(JP)[h flashmem-check japanese_cake].zip

Additional links:

6 replies on “Catching up part 2: Fish ‘n’ FlashChip”

Awesome work man. I had no idea these devices even existed! Sega really did make a lot of good use out of the Dreamcast hardware.

For patching game in order to boot it :
Have you replace at line :
RAM:8C0100DA : cmp/eq h’30, r0
and
RM:8C0100E0: mov.w#h’FF, r0
By
RAM:8C0100DA : cmp/eq h’00, r0
and
RM:8C0100E0: mov.w#h’00, r0
?

Absolutely brilliant, thank you for all of your work on this!!!! I’ve been waiting to see Fish Life running on a DC or emu from the minute I first heard of it years and years ago!!! So amazing!! Amazon is beautiful, but Red Sea would be completely over the top! Again, thank you so much!

Thank you so much for all your nice work and research on our beloved Dreamcast. A question for you so, do you intend to release new VGA patches? I’d really like to play without SCART an old game not really loved but that I hold dear : “Soul Fighter”. Thanks

Were Red Sea or any of the other GDs ripped? Been playing around with the extra PVRs in Amazon, and almost have it hacked into a decent marine version, but would be awesome to see the real deal in action!

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