Extending the demo: prototype Sonic Jam
There's more to Flash Sega Saturn #17 than meets the eye
Today we’re examining the Flash Sega Saturn Vol. 17 demo disc, released in 1997. It’s got a demo of Sonic Jam that lets you play a bit the first two 16-bit Sonic games1. And it lets you run around for 60 seconds in Sonic World.
People have been able to spot lots of differences between this demo version of Sonic World (from 1997-04-21) and the retail version (from 1997-06-02). A number of objects are in different positions, the music sounds a bit different, and the camera doesn’t work quite as well.
However, there’s more to see! If we disable the 60 second limit, we can activate various things that are in the final game: the Mission Panel, the blue check points, the balloons, and even the Giant Ring.
I made a patch that lets you check out these aspects of prototype Sonic World. Get it from SegaXtreme. Here’s a video!
Prototype difference
It’s minor, but I think some of this stuff was previously unknown2. The mission panel is over by the bridge instead of by the entrance in this version:
The giant ring is just above the mission panel rather than by the waterfall:
Here’s a balloon in a different place:
And a blue checkpoint:
What else can you spot that’s not visible in the 60 second preview?
Technical details: skipping the demo menu
The first thing you get when you load Flash Sega Saturn Vol. 17 is its menu. You have to select Sonic Jam to access the prototype. The text is in Japanese, but it’s not hard for an English speaker to figure out what to do - just hit start until it works.
We can improve things, however! Let’s make it so the title screen launches straight into Sonic Jam.
The memory address at 06045afc tracks the state of the menu system. The title screen is state 04, the demo select screen is state 11, the help screen is state 1C… there are a bunch of states.
The one we care about is 1F, which is used to launch the selected demo. Fortunately for us, Sonic Jam is in the default position. So if we set the state to 1F manually, we’ll launch right into it.
Setting a write breakpoint for the state address shows us that 060087e2 sets the state to 05 when we press Start at the title screen:
If we replace that mov 0x05, r1 with a mov 0x1f, r1, we’ll go directly into Sonic Jam.
Technical details: jumping straight into Sonic World
Sonic Jam’s menu system also has a state index. It’s at 0603600. To start up Sonic World, we need to set it to 20. The patch is:
06029992 e020That means “set register 0 to the value of 20.” The next instructions then write that value into the state tracker. Now we’ll see the demo disclaimer:
This says something like:
Sonic World Trial Version: This demo has been specially produced, and differs from the full version.
Well, yeah, that’s why we’re interested in it!
Technical details: missions and the Giant Ring
You normally just get one minute to run around in Sonic World. The demo uses the same “Hold A+Start at the title screen” challenge that is present in the final game. That challenge vexed me as a kid; I never managed to collect 100 rings in under 60 seconds3.
As Sonic World loads, it sets the value of 060FFC37 to 01. This is what activates the special 60 second mission. We can alter that to write a 00 instead. The patch is:
06049108 e000Now let’s turn our attention to this code snippet:
You don’t have to know much SH-2 assembly to see that the function has a return instruction at the top of it. That means it exits without doing anything - the logic underneath the return never executes. Let’s get rid of that return:
0605e384 0009Now the Giant Ring appears. Alas, it doesn’t work: rather than taking you to the credits, it spits you back out.
Outro
That’s it! Enjoy exploring prototype Sonic World. Here are some questions I can anticipate getting:
Q. Can I go in the buildings?
No. The files with their resources aren’t on the disc, so they crash as soon as you go into them. It’s possible to restrict the player from attempting this, but I decided to give the player the option to crash the game.
Q. Is there anything interesting outside of Sonic World?
Not really. I’ve poked around, and it’s clear that the menus are unfinished. Some of the modes, like the special stage results screen aren’t there. But I didn’t find any evidence of, say, Sonic CD being included.
Q. Is there anything different on the demo from Sega Flash Vol. 5?
No; it’s the same content.
Q. Anything else?
Feel free to add this information and these screenshots on your favorite reference site (Sonic Retro, Hidden Palace, TCRF, etc.) - it will save me the trouble.
Also, send me suggestions for what to look at next!
You can play the first three acts of Sonic 1 and two acts of Sonic 2 in the demo.
Nothing happens if you get 100 rings, alas!