Sonic Classic Collection DS: ROM Differences Research

Man, this brings me back. Sonic Classic Collection was the first place I experienced the classics.

 

Prototype? Was a prototype for Sonic Classic Collection ever found? We've had the original game ROMs dumped since 2010.

 

KazoWar made some videos with the ripped ROMs running on JenesisDS in 2010 and had them released, I couldn't find links now, though. I guess it's because people didn't really care much about them back then.

 

That's interesting. Is that NDS ROM available? I haven't heard of a prototype of Sonic Classic Collection before.

 

I had always assumed the Nintendo DS compilation was just emulating the original ROMs, albeit scaled down to look like arse to fit the DS' screen resolution. The compilation came out when emulated versions of Sonic 1/2/3 were everywhere - it's easy to see why it would be ignored.

But if UI elements were played with as these versions seem to suggest, that is indeed something worth documenting.


But then again so are the versions in Sonic Jam, and they've been waiting for documentation since 1997.

 

So here are my notes since I kind of helped out with this.
These are not prototypes in any sense. Neither to Sonic Classic Collection, nor the Mega Drive games. These ROMs are modified versions of the last Mega Drive releases, found in the release ROM of Sonic Classic Collection that you can buy off a shelf. Nothing here is a prototype.
As I mentioned, they're based on the last Mega Drive revisions, however modified. I like to call these revDS, for that. They have the mentioned changes of removing 2-player and options screens from Sonic 2 and 3 (They might still be in the ROMs, just inaccessible, play with a memory editor!)
They do in fact introduce new bugs as well. Here's a particular instance in Sonic 3
After the act 2 boss of Angel Island, if you spam the flame shield's air dash for whatever reason, the transition cutscene could trigger early. And before you get to the bridge, it's already gone, causing Sonic to fall. But the death plane doesn't exist, neither does the level change trigger. Sonic will only die from being below the screen for too long:


Sonic 3 on the Mega Drive is smart though and won't trigger the cutscene early just from some silly shield spam.

What I found really interesting from the revDS games is that they are unchanged in ways that don't necessarily make sense.
For starters, audio is streamed through files called snd_SonicX_trx.mods and snd_SonicX_sfx.mods, rather than the emulator actually emulating the Mega Drive's sound (To be fair it's a difficult thing to do), but the audio is left in these revisions. Maybe it isn't too surprising though, it'd be a lot of effort to cut out the sound drivers entirely just to optimize the size since audio is streamed. But what I found odd and for valid reasons, is that you can pause in-game. This is weird because in Classic Collection, you cannot use the start button in-game to pause it, Classic Collection makes you tap an icon on the touch screen which simply freezes the emulator. This means that the emulator actually checks what's going on in-game to prevent you from pausing with the start button, but still letting you use the start button in menus and whatnot.

 

I am very confused.

First, I downloaded these ROMs and compared them to the ones in this thread -- they're a perfect match, so these would appear to be final and not prototypes as purported.

Second, except for the invalid opcode shenanigans detailed here, there are very few byte differences between these and the regular Mega Drive ROMs, all of them cosmetic in some way, and suggesting the games were hex edited by the developers of the DS collection. I've gone through and documented all of these changes below, and the fact is none of them should affect the behavior of the games at large in any way, so I don't understand where you're getting these absurd bugs or sped-up gameplay from.

All ROMs have a recalculated checksum at $18E. Individual game changes follow.

Spoiler: Sonic 1

$0033A: The branch that would jump to a checksum fail trap now leads to the 'OK' code path.
$1EC6C: Replaced Enigma-compressed title screen plane mappings to move copyright text closer to the center. This is not foolproof, as now there is garbage to the right of the text.

Spoiler: Sonic 2

$00346: The branch that would jump to a checksum fail trap now leads to the 'OK' code path.
$03B58: Title screen copyright text written to different place on the plane A buffer, so it's moved down and closer to the center.
$03D6E: EHZ demo sets the 2P mode flag to off rather than on. Tails still runs his own inputs though, goes off-screen, respawns, and desyncs the playback.
$03DF4: Replaced Nemesis-compressed art for title screen options.
$0BCF6: Removed spaces around "TAILS" in the pre-title-screen card, to take up less of the screen.
$13638: This one's neat. Changes all references to the Title_screen_option RAM variable to point at the low byte of Player_option instead. This effectively makes the cursor control the selected character, and the initial cursor position also reflects which character you last chose. It still ANDs away everything but the low bit though, so choosing Tails and returning to the title screen causes Sonic+Tails to be selected.
$13B70: Changed title screen sprite mappings to go along with new Nemesis art.
$14C08: Changed title card mappings to move the SONIC THE HEDGEHOG text a bit to the left.

Spoiler: Sonic 3

$04088: Changed X/Y position of title screen copyright sprite.
$040F8: Okay, this is stupid. This change prevents the title screen option from being decremented when pressing up.
$04110: And this one prevents it from incrementing when pressing down. But the object still processes the controller inputs, and it still refreshes the selected menu option and attempts to play a sound effect.
$04132: Except this changes the sound effect to zero, so nothing is heard.
$042DC: Changed title screen sprite mappings to remove the COMPETITION option.
$0434E: Smushed up title screen copyright sprite mappings, to take up less of the screen.
$0762A: Special Stage - draw initial sphere counter higher and further to the right.
$07640: Special Stage - draw initial ring counter higher and further to the left.
$07944: Special Stage - draw sphere counter higher and further to the right.
$0795E: Special Stage - draw ring counter higher and further to the left.
$07DAA: Special Stage - changed sprite mappings to move HUD icons next to new counter positions.
$2CD7A: Changed title card sprite mappings to move the level name a bit to the left. Note that this change doesn't apply to Sonic & Knuckles, so enjoy your playthrough of Mushroom Hil

Spoiler: Sonic & Knuckles

$05F64: Changed title screen sprite mappings to move TM symbol from the side of the logo to above it.
$05F6E: Smushed up title screen copyright sprite mappings, to take up less of the screen.
$0839C: Special Stage - draw initial sphere counter higher and further to the right.
$083B2: Special Stage - draw initial ring counter higher and further to the left.
$08882: Special Stage - draw sphere counter higher and further to the right.
$0889C: Special Stage - draw ring counter higher and further to the left.
$08E32: Special Stage - changed sprite mappings to move HUD icons next to new counter positions.

EDIT: I assume the DS collection also patches the lock-on titles separately, but I haven't looked at the lock-on patches provided in the aforementioned gbatemp thread yet.

EDIT THE SECOND: Wait, now that I've parsed that previous post, I'm wondering -- isn't that just the bug where if you go from the act 1 Knuckles cutscene all the way to act 2 one without ever reloading the level (so no deaths, bonus or special stages), the button spawns in the same slot as act 1 Knuckles, "detects itself" and breaks the bridge before it's supposed to?

Or something like that, anyway. I'd have to look at the code tomorrow. Did you try any of what you described on a vanilla Sonic 3 ROM?

 

I'm personally confused as to why the devs of the collection didn't just make the emulator properly fit the screen, such a fuss to reposition all these things.

 

I'm surprised this is new information for you guys considering I dumped these back in May, here's a link to my topic about it (If I am not allowed to post links to other forum threads outside Sonic Retro, I can remove it):
https://gbatemp.net/threads/sonic-classic-collection-dumps-and-opcode-fixes.565585/

I do not know who told anyone these were prototypes, but that's clearly not right. All of these versions are all retail builds that the public got via official means like the game cartridges. There isn't anything too special behind them, as for the bugs, these bugs aren't from the ROMs themselves, they are from the emulator and other audio based assets in Sonic Classic Collection that produce these bugs that generally aren't present in these titles standalone. Running these titles on official hardware or on an emulator will result in the same performance and results as the original dumps of the games. The only notable changes are the slight graphical changes (was done to account for the size of the Nintendo DS display), and the opcode changes (the reasons for this isn't necessarily clear, however I would like to believe it was just a way for the developers to prevent people from running around with these games so easily).

Checksum validations for Sonic the Hedgehog and Sonic the Hedgehog 2 were edited to not work when launching the titles, even though the checksums did in fact change somewhere during their edits, they are clearly still incorrect for a few reasons (mainly the opcode changes). Sonic the Hedgehog 3 and Sonic & Knuckles however didn't need any tweaking as the checksum validation functionality for both was essentially scrapped because of how slow games would boot because of it.

Multiplayer wise, they weren't removed, only merely phased out. Sonic the Hedgehog 2 just had some option tweaking done so it worked the way it did in the game. Sonic the Hedgehog 3 only had edits to disable the ability to scroll to the next option let alone see it. In doing so though it rendered the Sound Test option to be unable to be selected, however it's still fully functional. Due to the way the emulator is however, multiplayer game modes are heavily bugged, however when dumping the games and using them on a proper emulator and or on real hardware, they function just as they were intended.

The lock-on variants of the respective titles are handled dynamically. Considering the Nintendo DS only had 4MB of RAM to work with, running a full 4MB SEGA Genesis ROM isn't going to work, so the developers designed it so depending on what happens in the game or where you are in the game, data is dynamically called for on the fly, which allows you to obviously play the game as you normally would.

NOTE:
The bugs presented via the screenshots provided above from the earlier Sonic the Hedgehog 3 comment, this only happens when you dump the game too early without actually allowing the opcodes to properly update. Some of the data for Sonic the Hedgehog 3 was made dynamic in Sonic Classic Collection, so you can't just dump the game and expect it to work correctly as is.


Screenshots:

Sonic the Hedgehog 2:

Spoiler: Dumped and Emulated

Left image is the original options, right image is the fixed options.

Spoiler: Sonic Classic Collection

Left image is the original options, right image is the fixed options.

Sonic the Hedgehog 3:

Spoiler: Dumped and Emulated

Spoiler: Sonic Classic Collection

Sonic the Hedgehog 3 & Knuckles:

Spoiler: Dumped and Emulated

Spoiler: Sonic Classic Collection

MAJOR EDIT:
Turns out @LadyLeia fibbed a tad bit (maybe they were given the stuff still, but someone isn't sourcing where these came from either way) and actually took what I actually posted in that GBAtemp thread, patched the ROMS respectively (checked against verified hash data), and reuploaded it. How I know this is because the Sonic the Hedgehog 3 data is dynamic in Sonic Classic Collection as I stated, and the chances of others figuring that out right away and getting the exact same dump isn't plausible (not even KazoWAR's dump worked exactly like mine, so much so that it wouldn't run on jEnesisDS based on his video, mine however can based on the video footage I made and slapped into the same thread).

 

Well, at least now we have all the changes documented

 

Because the screen resolution of the Nintendo DS is 256x192 pixels, and the Genesis/Mega Drive is 320x224 pixels. Crunching down the resolution would look like arse.

 

They crunch it down anyways, though

 

They scale the resolution down vertically, but do so using special hardware tricks like skipping lines etc. Horizontal interpolation would require rendering the image in software, making the games unplayable, as the framerate would tank.