The last few days I’ve been fooling around with the debug modes in a few Virtual Boy games.
The biggest discovery was that Vertical Force’s debug menu is fully accessible in the retail game without hacking. I was also able to make a tiny bit of progress getting SD Gundam’s debug menu up, and lastly I made a small custom patch to change how the Virtual Bowling debug menu is launched. I want to give Parasyte huge credit for the Vertical Force discovery and my little Bowling mod, as both relied heavily on that original hacking work done some 20 years ago.
Vertical Force
Notably, Parasyte predicted in the readme for the original debug mode hack that, given its high-quality presentation, the menu might be accessible in-game. Well, it’s nice to know that hunch was right, all these years later! To access the debug menu, open the Config menu then press the following sequence of buttons:
- Left D-Pad Left
- Left D-Pad Left
- Right D-Pad Right
- Right D-Pad Right
- Left D-Pad Up
- Right D-Pad Down
- Left D-Pad Up
- Right D-Pad Down
- L
- R
- Right D-Pad Right
- Right D-Pad Right
- Left D-Pad Left
- Left D-Pad Left
- Right D-Pad Up
- Left D-Pad Down
- Right D-Pad Up
- Left D-Pad Down
- R
- L
If you don’t want to remember all that, there’s obviously Parasyte’s existing hack here on virtual-boy.com, which forces the debug menu to load on startup. Alternatively, there’s now a patch on The Cutting Room Floor’s Vertical Force page which replaces this button sequence with a single press of Select on the Config screen.
SD Gundam: Dimension War
It’s been known that SD Gundam has some sort of stage select for a while now, but as far as I know nobody has managed to trigger it in-game. I wasn’t able to get the menu working, but I did manage to get it to at least load and display on-screen.
The function at 41EE8 in the ROM is responsible for the debug menu. I wasn’t able to find if there’s anywhere in code which jumps to this function, but I’m just goofing around in an emulator. Somebody more capable (and with access to a disassembler?) may very well be able to take this further and get the debug menu fully working.
That said, you can force the game to jump to this function to at least see the menu, albeit without it actually functioning. Editing offset 7FD0 in the ROM from 01 AC E4 FE (jal fff27eb4) to 03 AC 18 9F (jal fff41ee8) will replace the main menu screen with the “SELECT GAME MODE” menu. From here, you can’t really do anything. A/Start will boot the game, but it’s not otherwise possible to navigate the menu or do anything useful. I’ve attached a screenshot of this menu, since looking at a screenshot is about as good as doing it for real with this half-baked modification.
I haven’t bothered making an IPS patch for this change because it’s basically useless, but I think it’s very likely somebody knowledgeable could get it into a completely working state. Who knows, it could even be like Vertical Force where the debug mode is accessible without hacking but nobody’s figured out how to open it yet.
EDIT: I finally managed to figure out Bob Vanderclay’s V810 Disassembler and got SD Gundam disassembled. I can confirm that there are no jumps to the debug menu function anywhere in the game (unless they’re obfuscated, but I’ll get into why I think that’s unlikely). What there is, however, is a dummy function at 7B8C which immediately jmp [lp]s, i.e. calling the function simply returns. There are also 28 calls (!) of this function scattered throughout the game’s program, including in conspicuous places like the start of the main menu function. Every single one of them is additionally stepped over with a jr, so the dummy function itself is never actually called.
My supposition is that the central portion of the game’s debug code lived in this function, which was compiled out for retail. This function would have handled jumping off to the various debug functions based on what functionality was called for at any given point in execution. This means it’s substantially more difficult for debug to be re-enabled in the retail build, because whatever this function used to do is completely opaque to us from the perspective of the final build. Depending on how thoroughly the rest of the debug code was scrubbed, it could be theoretically possible to restore the functionality by reproducing this function blind, but that would be a huge undertaking and require somebody with much greater ability than I have. Sorry for the downer result!
Virtual Bowling
This one is probably the least interesting, but I made a small hack to adjust how the debug menu is launched in Virtual Bowling. Parasyte’s patch here on virtual-boy.com simply forces the debug menu to open on start-up. This sort of means you need to keep two separate Virtual Bowling ROMs around depending on whether you want debug today or not. My modified patch instead checks whether you’re holding the Select button on start-up. If you are, the debug menu is triggered, otherwise the game boots normally. You can download this modified patch from The Cutting Room Floor’s Virtual Bowling page.
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Oh, that’s odd. It should be that if you hold Select while powering on the Virtual Boy, it prints “DEBUG” in the bottom right (screenshot attached) and you can use all the debug features documented in the Guides section here on virtual-boy.com. The easiest thing to check is that during gameplay, L + R together skips the current floor.
It works on emulators, but maybe the Virtual Boy doesn’t start registering input until after I do my startup check?
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Thanks yet again for all your testing. Really odd the issue with mine and HorvatM’s patches in conjunction. I’ll have to look into it some more. For now, I’ve published the next set of updates for Red Alarm, Space Squash (same as the version in this thread) and V-Tetris.
Ironically, the Red Alarm patch is aimed at handling the “high score protection” feature I was talking about earlier when used in conjunction with HorvatM’s patch, but it doesn’t (or at least shouldn’t!) do anything to fix their actual incompatibility. In older versions of my patch, I was checking if the user had pressed Select 60 times, the same way the base game detects that debug mode is active. Now, I’m specifically reading the byte that says how many times you need to press Select, so even if that value is hacked to 15 or 90, it should still work. But again, this doesn’t resolve whatever is going wrong in terms of them actually working together.
Re: Space Squash, which high scores are you looking at specifically? I deliberately don’t save your current score when saving and continuing because that would be easy to abuse to get a much higher score than you actually earned. Instead, scores only get saved when you game over (or finish the game) and enter your initials. The high score table shows up if you sit on the title screen for a few seconds looking something like this:
When you Continue a game from the main menu, your score will always be zero. I’m open to changing that in an update, though. The problem is that allowing you to keep your score when Continuing would basically make all scores meaningless. Did you achieve that by never losing, or by losing a bunch of times and continuing over and over until you did well? Maybe there’s a decent compromise solution here, like your score gets dropped to zero if you run out of Retries, but otherwise it carries across the save? People could still exploit it by just shutting off the game before running out of Retries, but it’s a single-player game so it doesn’t really matter if people want to cheat their high scores.
Yes, I mean the highscore after you loose a game, exactly the same screen you show in your screenshot.
I played until the second area to see if the continue works, and then lost the game by purpose. I then entered my three letters in the highscore list, turned off the system and restarted it and the high score was gone.
