Sonic CD 510 with enabled Special Stage

So yeah, while working on my disassembly I decided to take a break (lolyeahright) and see what makes the special stages in Sonic CD tick. Well, turns out the SP code sets a flag as demo, no matter what, since it wasn't intended for play. Well, since I couldn't find the flag, I went in and reversed the operations on all of the involved Bcc opcodes. What I'm left with is a (fully fuctional?!??) special stage in Sonic CD 510. Also, I edited a table somewhere to allow the Time Attack selection to load up the special stage. Once you start the special stage you're stuck in it because the same flag that controls the automatic movement controls whether the timer works or not. Anyway, controls are a bit different, left is right and right is left first of all, this confused the heck out of me. Also, Sonic seems to be stuck in an endless bounce, which you can only get out of by holding C down. Holding B down makes Sonic come to a complete stop. A doesn't do anything as far as I can tell. It seems that the fan and bumper sides are implemented fully, water and the chomper floor pieces cause Sonic go become invisible, likely placeholder code for losing rings. The rough areas act the same, slowing Sonic down. Springs don't work yet. What made me sad is that the oil slicks aren't implemented, they're just normal ground like everything else. Well, tl;dr, have fun playing with this for all of 3 minutes. :P

http://www.mediafire.com/?m00jx79k9oz4623 F that

Again, just go to Time Attack to enter the special stage

Edit: http://www.mediafire.com/?v2hk31yn3101v3k New link, this one works everybody ;D (I changed it though, don't hit time attack, just wait on the title screen for it to load up, and at any time press start to go back to the title screen.

 

After more work I found the flag that controls which stage loads (again, kinda, I can't make the game load the special stage any way other than the demo way, but it'll load different artsets)

Change word $118D24E to:

$94 - (This is a different chunk of code, but it loads the same art...hmm)
$108 - The 3rd time stone background
$18A - The 4th time stone background

(Note, the layout remains the same with this flag switch, all it does is swap the palette and background)

Edit: Found the difference on $94, no Developer has a nap text.

Edit2: Mixed up the third and fourth up there, also found this:

Change word $118D934 to:

$66 - 3rd time stone background rotation speed
$12E - 4th time stone background rotation speed

(This prevents sheering)

Also, the original value for both these flags if you forget is $0E

Edit3: (Gah, I'm on a roll :D)

Change word $118DB04 to:

$48 - 3rd time stone bubble cycles
$FA - 4th time stone waterfall cycles

Same as above, original value is $0E

 

Because this isn't about disassembly as much as it's about a finding and a release of an ISO featuring new content. Consider it a hack in the sense that the PRESS START button is a hack of Sonic 1. :P

 

Yeah, I like that. I hope I can find code for UFOs or that yellow balloon or something in all of this.