Sonic Adventure DC-HD first release

Update 2024/06/29: This tool has been superseded by the Dreamcast Image Builder.

Sonic Adventure DC-HD is a new way to play the Dreamcast version of SA1 on the flycast emulator.

You can play SA1 with the following improvements:

  • The game runs at 60 FPS during gameplay without framerate-related glitches (hopefully).
  • Widescreen hack without model clipping or HUD stretching (some HUD stuff is offset though – this will be fixed eventually).
  • All videos can be skipped by pressing Start, not just the intro.
  • Cheat code to disable all cutscenes.
  • If you cannot run in a straight line with your controller/keyboard, there’s an optional patch for that.
  • Less choppy ocean in Emerald Coast (similar to Dreamcast Conversion for SADX PC).

Sonic Adventure DC-HD is distributed as a patcher program which you use on the original GDI of SA1 (US 1.005, animated title screen) to produce a patched version. It also comes with a cheat file that you need to load in flycast if you want to use the widescreen hack. Follow the instructions on the repo for more details.

This project is a work in progress. Not all features are complete and new features may be added in the future.

SA1 DC-HD has been tested on the standalone version of flycast on Windows and Android. The modified image is only meant to be used on the flycast emulator. 60 FPS and the widescreen hack will not work properly on other emulators or real hardware.

A “month without SADX” challenge

I decided to make August an “SADX free” month. This extends over to GitHub, Discord etc. I might fail on the very first day of August or keep it and come back in September, or later, I don’t know. But for now, it’s time for a break. Bye!

Skip All Cutscenes code for Sonic Adventure (Dreamcast)

This is a CodeBreaker code for SA1 US 1.005 that disables all cutscenes. It works exactly the same way as the “Skip All Cutscenes” code in SADX Mod Manager.

010496B4 0900

Cutscenes are removed by nopping the function call that starts the cutscene code, which makes the game assume the cutscene has finished playing. The address of the call is 0x8C0496B4.

There are a couple of small glitches when this code is used. For example at the start of Sonic’s story you can see Sonic in Station Square before the screen fades out and the fight with Chaos starts. This is how it’s actually programmed – the game loads Sonic into Station Square before initializing the cutscene. You can see it briefly when you start Sonic’s story without the code. A similar glitch happens in Station Square in Knuckles’ story.

There are some other potential applications for this code. For example, a conditional code could be made to activate cutscene skip when a certain button combination is pressed, and restore original behavior when it isn’t pressed. That way you could skip individual cutscenes by holding a button when the cutscene is about to play. It could also be made into a simple toggle. Of course it’s not as straightforward as simply pressing a button during the cutscene to skip it, but it’s still pretty good.

SADX Debug Mode version 2.0

Today I’m releasing an update for the Debug Mode mod that adds a free camera mode.

Using the free camera mode

Press Y on the keyboard to enable free camera. When the free camera mode is enabled, you can use the mouse to move the camera around. The control scheme is similar to the one used in 3D editors in SA Tools.

  • Move the mouse to rotate the camera.
  • Hold Left Shift and move the mouse to move the camera.
  • Hold Control and move the mouse up and down to zoom in and out.
  • Press both Left Shift and Control to lock the camera in place. Press them again to unlock it.
  • Press Numpad + and Numpad – to change camera speed.
  • Press Y again to re-enable vanilla camera. It will remain locked in place until the character touches a camera trigger.

I would like to thank Speeps for providing the source code of an unreleased mod with the the original free camera code, which became the basis for the free camera mode in this mod.

Sonic Adventure VMS + Chao Editor first release

Today I’m releasing a new tool based on the original SA1 DLC editor. This tool has the DLC editor integrated, but its functionality expands to cover more VMS files in SA1. Eventually I would like it to support all of the formats described here, but the highlight for today’s release is the inclusion of a new Chao editor.

Like the original DLC tool, the updated editor will be included in SA Tools, which also have a big update underway.
UPDATE: It’s been released and is now included in SA Tools.
The Chao editor is experimental and will be updated as more information on SA1 Chao data becomes available. There is no documentation for it at the moment, although the most important data should be self explanatory.

The Chao system used in SA1 is the least researched of all Chao games. There are several Chao editors for SADX and SA2, but the only Chao editor for the Dreamcast version of SA1 was Tyro’s VMU editor that requires running on an actual Dreamcast VMU or a VMU emulator, which I found inconvenient. Besides, there have been some updates regarding SA1 Chao data (for example we now have the full SA1 Chao data struct from SADX X360 symbols), and I wanted to make use of that new knowledge to help advance SA1 Chao research. Although several aspects of it are now known better, Tyro’s notes on SA1 Chao data were one of the most important sources of information for developing the editor. I would also like to thank the Chao Island member UltimaNumber, who kindly shared the bits of information I was missing and explained how SA1 Chao data works.

The tool can import all Chao VMS data. Data produced by the Japanese version is also supported:

  • SA1 Chao Garden save file
  • Download Data (Black Market Chao)
  • Chao Adventure (created when you take a Chao out for a walk)
  • Upload Data (created when you hold Y+A as the Chao goes in the transporter)

At the moment saving is only supported for Chao Adventure and Download Data, but you can export selected Chao from the garden save file as Download Data or Chao Adventure data. There’s also an option to export files with headers used by the Japanese version of SA1.

As Chao data is rather complex and the editor is experimental, there may be some bugs, especially with saving data. Also, expect UI changes in the future.

I’d like to thank Speeps for providing a screenshot of Buddy the Chao that I used as an icon for this tool.

Sonic Adventure Black Market Chao

The first Sonic Adventure on the Dreamcast had a Black Market just like the sequel. The archived version of the original website still has the pages and CGI scripts for it, as well as VMU files, which we’re going to look at today.

I didn’t access the Black Market back when it was online, but I’ve heard that the US version never worked because of some bug. The messages from Chao Doctor all the way to January 2000 mention that the Black Market was about to launch, and the comments in the CGI script used on the website suggest it was indeed broken at the time of archival:

The Japanese version was functional though, and it was possible to download several jewel Chao. The Ruby and Emerald Chao didn’t have any emblem requirement. It looks like they were given out “for free” to celebrate the Dreamcast’s US and EU launch anniversaries. However, according to this page, the Emerald Chao was released during an event “Magical Garden: Yume no (‘Dream’) Dreamcast Festival” that took place on March 27, 1999. I can’t find any other information on the event so I’ll have to leave it there for now.

The Amethyst Chao was unlocked when you had 100 emblems. The Sapphire Chao isn’t referenced in the pages or scripts but its VMU data exists. Apparently the US version was going to add a new “NiGHTS” Chao that would also cost 100 emblems. Although the NiGHTS Chao is referred to as “very special Chao”, it’s actually a regular Fly type Chao with animal parts rather than a unique character Chao, which SA1 doesn’t support anyway.

Chao downloads are stored in 8-block VMS files, and Japanese files have a different header although the data is compatible between all versions. There’s a script on the website (likely used for Chao daycare) to generate Chao VMS files, and it alternates between Japanese and US headers, which are stored as binary data on the website. The header is set up like a VMU game header, similar to Chao Adventure. Here are all the files found in the site’s archive:

DescriptionVMI fileScreenshotEmblem requirement
Emerald ChaoCHAO_EME0
Ruby ChaoCHAO_RUB0
Amethyst ChaoCHAO_AME100
Sapphire ChaoCHAO_SUF?
NiGHTS Chao (US only?)KNIGHTS100
Download all of them here

I’ve also made Chao Download data for BUDDY, the developer Chao mentioned in my previous post. Download it here to get it in your copy of SA1 DC.

List of VMU filename references in Sonic Adventure

There are a lot of mysteries about Sonic Adventure’s files on the VMU, some of which we’re going to unravel today. I’d like to also use this post to list known VMU filenames in SA1 for future research.

Let’s start with the better known stuff. The main save file is called SONICADV_SYS in the original Japanese release, and SONICADV_INT in all other versions. The newer versions contain text and voice language settings which aren’t available in the original Japanese version. Normally the Japanese version doesn’t load US/EU/International save files, and vice versa. However, the game will recognize the other version’s save file if you rename it.

Now let’s talk about Chao files. The main Chao save is called SONICADV_ALF and is compatible between all regions. When you take a Chao out for a walk using the VMU-shaped transfer machine, the game creates a file called SONICADV__VM on the VMU. This file contains the VMU game Chao Adventure with the Chao’s data written directly into the game file.

The filename SONICADV__VM was also used for Chao downloads from the website. In the Japanese version of the game you could download rare Chao (Sapphire, Ruby, Emerald) from the website if your main save file had a certain number of emblems. These are discussed in a separate post.

Upload Data

There’s also a bunch of files that are created on the VMU at certain points in the game. These files were meant to be uploaded to the official website using the game’s built-in web browser. Among such files were Chao, level clear times and results of DLC challenges. They contain an HTML page with a hidden field that contains encrypted data encoded as a Base64 string. The encryption is the same between these files and DLCs.

The Japanese version had different strings for the webpage so the embedded HTML is different from later revisions, also the Japanese version uses different filenames. Here are all of them:

Filename (JP)Filename (US/EU/INT)DescriptionHow to create
SONICADV_H00SONICADV_H07Chao Upload dataHold Y+A when a Chao is going into the transporter until you hear the ring sound
SONICADV_H01SONICADV_H04World Ranking DataHold Y+A on the file select screen until you hear the ring sound
SONICADV_H02SONICADV_H05Twinkle Circuit DataCreated automatically when you finish the DLC Twinkle Circuit course
SONICADV_H03SONICADV_H06Event Result DataCreated automatically when you finish a DLC challenge

Hidden Chao on SA1 US GD-ROM

Interestingly there are files SONICADV_H00.BIN and SONICADV_H04.BIN in the root folder of SA1 US GD-ROM. These appear to be earlier versions of the data produced normally by newer revisions of the game. Apart from using the Japanese version’s naming scheme they have some differences in HTML compared to the regular files. While it isn’t compatible with either version of the game, the interesting part is the actual data stored in these files.

The Chao file contains a baby Chao called ♥BUDDY♥ that was submitted by Yep, there’s been a Chao hidden on the game’s disc all these years. Here’s what it looks like:

Stats: Swim: 19 Run: 17 Fly: 17 Power: 27 HP: 13 Max HP: 17

Eventually you’ll be able to edit Chao upload and download data, including this file, as well as the main Chao save. I just need to get to writing a Chao editor for SA Tools.

Character Voice Packs

When one of these files is placed on the VMU, the game changes the character voicing the menu screens. The files themselves don’t have any meaningful data other than an icon, a description and a single string Team Andromeda. The game seems to set the voice mode based on the filename. Again, the Japanese version looks for different filenames, so there were actually 18 unique files for voice packs! Do we even have their Japanese versions archived?

Filename (JP)Filename (US/EU/INT)Description
SONICADV_V03SONICADV_V13Knuckles’ voice
SONICADV_V07SONICADV_V17Dr. Eggman’s voice

Events and Challenges

A lot has been written about SA1 DLCs, and they are now fairly well understood, up to the point that you can make your own DLCs that will work on an actual Dreamcast without hacking the base game. So here I’m going to talk about things that are a but more obscure.

One major limitation of the DLC system in SA1 is that you can only have one custom model. While I haven’t been able to get the game to load more models, I got it to load a model that isn’t stored in the DLC file by editing the pointer in the DLC file’s model binary to make it point to a different location in memory. It’s still just one model per DLC and you have to supply its textures separately but at least you can load stuff outside of the DLC file if you really want to. Maybe it’s possible to add more pointers and make the game load them somehow? I’ll look into that sometime soon.

The filenames for the DLCs are SONICADV_aaa, where aaa is a number from 000 to 999. IDs from 000 to 200 are reserved for DLCs that only have text in Japanese. Early events released in Japan (Famitsu challenge, QUO challenge etc.) only contain Japanese message strings, and their string table is smaller compared to later events that had text in other languages. However, these old events still work with newer versions of SA1 with Japanese text displayed correctly regardless of the game’s language setting. The game doesn’t load strings for other languages if the DLC ID is lower than 200. This is why there is a gap between Japanese and international event filenames: the last Japan-exclusive event was called SONICADV_003 and the first international event was called SONICADV_501 (though SONICADV_200 would’ve worked too).

The Weird Stuff

The game’s main binary has several filename strings that suggests some interesting functionality. Earlier this year we learned from Exant’s fascinating discovery that we can still activate the game’s built-in lighting editor that looks like this:


Apparently this editor can load lighting files from the VMU, and that functionality seems to be still in the game, we just need to learn how to activate it. The palette file is supposed to be called SONICADV_P00, and the SL file is SONICADV_S00 (in the Autodemo they’re just PL_ and SL_). It’s possible that numbers other than 00 were also used. There is a function loading these files at 0x8C011D46 (US 1.005). It also seems like LANTERN_PALETTE and LANTERN_SOURCE were VMS titles, while LANTERN/パレット情報 and LANTERN/環境情報 were VMS file descriptions. I’ll experiment with custom VMS files to see if the game picks them up.

There are also some strings suggesting there was VMU to PC transfer at some point. The filenames used in that transfer were SONICADV.VMS and SONICADV.DL0. Doesn’t look like it’s used, but who knows, maybe we’ll recover it eventually.

Sonic Adventure patches (Better 60 FPS + drift fix)

If you’re interested in hacking Sonic Adventure, you’ve probably seen 60 FPS and widescreen codes for the Dreamcast version floating around. The problem with 60 FPS codes for SA1 is that they make cutscenes run at double speed. Here’s my understanding of why it happens and a solution for version 1.005 (US, animated title screen).

The game uses two values to control framerate and speed: the frame increment (8C754EBC) and the multiplier (8C754EC4) used in physics and other things. The frame increment controls the actual framerate (1 for 60 FPS, 2 for 30 FPS), and the multiplier speeds up or slows down the physics to match it (1 is original speed). The Dreamcast version runs at 30 FPS everywhere except menus and Twinkle Circuit. In 30 FPS mode the frame increment is set to 2, and the multiplier is also set to 2 to speed up the physics to match the reduced framerate. In menus and Twinkle Circuit both values are set to 1, so the game runs at its original speed at full framerate.

This would be all fine, but the problem is the cutscenes. They are programmed in double speed, so the game sets the frame increment to 2 and leaves the multiplier at 1 to get them to work at half speed. This is also the real reason SADX cutscenes are still capped at 30 FPS – updating them would require fixing the timings in all functions used by cutscenes to work properly at 60 FPS, which is a lot more work than simply unlocking the 60 FPS mode in levels like the developers did.

The problem with existing codes is that they don’t account for the above and simply force both values to 1, which causes cutscenes to run at double speed. To fix this, instead of changing the values directly we can do the same thing SADX developers did, and change them depending on what happens in the game. Like in SADX, there is a function that is called to set the required frame increment and multiplier. All we have to do is patch the arguments that are passed for this function when the game loads levels, and leave cutscenes alone. Here are the addresses for version 1.005 (US, animated title screen). Just change the bytes at these addresses from 2 to 1, and the game will set framerate modes like SADX. If you use Demul with Cheat Engine, replace the starting 8C with 2C.


Here’s also a code that you can add as a custom cheat for redream. It’s a regular CodeBreaker code so you could use it on other emulators or on real hardware.

cheat=0204956E 420BE501 0204E662 4F22E501 02054736 430BE501 02082AAE 420BE501 0209A1D2 D252E501

There are still two problems remaining with the 60 FPS code:

  • The hardware cannot handle the game at 60 FPS most of the time (sometimes it struggles even at 30 FPS), so you will get a slow motion effect like in older SA1 preview videos. Unfortunately this also affects emulators – for example, at the moment the game does not reach full framerate in redream. There was a similar problem with Sonic Colors, which the Wii can’t handle at 60 FPS, but that was resolved with Dolphin’s overclock feature. Maybe we’ll get that in Dreamcast emulators someday?
    UPDATE: It seems to be perfect on flycast, no slowdown at all.
  • There are glitches that happen when the game runs at 60 FPS. It’s possible that some things in the game were added after the decision to switch to 30 FPS was made, and perhaps they were only tested at 30 FPS. A lot of such glitches appear in SADX. For example, the Leon badnik almost never attacks the player and disappears too fast. There are visual glitches too, for example Tails’ tails are too fast, and the background in the tornado section in Windy Valley loses the multi-layered effect for one layer. A lot of these glitches are fixed in the Dreamcast Conversion mod for the PC version, and it’s also possible to fix them in the Dreamcast version if we really want it. Interestingly some issues that affected DX at 60 FPS don’t affect SA1 at 60 FPS – for example, the Egg Hornet engine sound glitch.

There’s another issue with SA1 on emulators related to not being able to run in a straight line with the keyboard and some controllers. You can fix this by disabling analog interpolation by writing 00 00 00 00 to 8C051278 and 8C051430. CodeBreaker code:

02051278 00000000 02051430 00000000

It’s not an ideal solution but that will do for now. A better fix may show up very soon.

Sonic Adventure DLC tool: GUI version released

I’ve updated the SA Tools with a new version of the SA1 DLC tool that lets you create and edit VMS files for SA1 on the Dreamcast.

Some documentation is available here.

Apart from the GUI making it easier to edit things, this version also fixes several issues with the original tool that made it produce incorrectly aligned VMS files. Now it should be possible to modify and rebuild any of the official DLCs, or create completely new DLCs from scratch.

The tool ended up being a bit more complex than I originally anticipated, and testing it was a challenge. I’d appreciate it if you try it out and let me know on x-hax if you run into any issues. Have fun!