Patching Jaguar ROMs

[Cyrano Jones]

Hi there...

With the source code for several ROMs available (although not exactly necessary) I'm considering looking into patching some of the jaguar games up a bit, eg:

Better controls in Checkered Flag, or infinite lives in Bubsy (or whatever game - if there isnt a cheat built in) - or maybe start on any level in Cannon Fodder? - anyone interested in this being done?

[sh3-rg]

Holy hell fire yes!

I've read about patching before on here I think & the Checkered Flag thing is actually a very timely thing to mention!

I'm all for this, I had a look around a week or two back at SNES stuff that had patches. There's quite an elegant way of distributing patches without the need for the roms, so you can do it without worry of being accused of anything naughty.

CJ back on jaguar all these years later - that's what the jaguar needs!

[remowilliams]

Hell yes is right!   

<in Gauntlet speak mode>  Checkered Flag needs new controls badly!

Seriously anything you could do would be awesome, and very appreciated.  Now that many folks have the ability to run cart binaries on real hardware thanks to the Skunkboard, there's a bunch of people who could really use this kind of stuff. 

[jmetal88]

Yes!  Better CF controls would be AWESOME!   

It's actually one of my favorite games as is, but making it easier to just pick up and play could easily push it up in the top 3.

[Sauron]

Better controls for CF would do a lot for that game, I think. Although the framerate is still horrid, it would then at least be playable.

[remowilliams]

Yeah I wouldn't expect a miracle, but being able to actually steer might be nice.   

[doctorclu]

Checkered Flag would be great to have better controls, even rotary support if possible.

I want Wolfenstein with selectable knife.

And Bubsy... working on decompiling now on a thread near you. 

[Fredifredo]

Few years ago, I made my own patch of Fever Pitch Soccer ...
I would change some team names and colors but not found on the rom...
I changed name players and intros screens only...

[doctorclu]

That kind of stuff is always fun to do with the hex editor.

I made a ElfQuest version of Archon for the Atari 800
Changed Star Raiders to say different text.
Modified Wizard of Wor, Dos 2, and a few other things. 

[Fredifredo]

Brett Hull Hockey would be nice to patch ! Most of the graphs are in BPEG, and text in ASCII...

[songbird]

I have to admit, I enjoyed the challenge of patching Total Carnage a few years ago (even though it took many more late nights than I would have thought at the beginning). Since most Jaguar games heavily utilize the 68k and they typically copy the code to RAM prior to execution, it's not too hard to figure out what parts of RAM are being used and which parts are available.

Then, it's a matter of doing some detective work... disassembly / hex searches to locate certain key addresses, like the obj list or the joypad read or whatever. Figure out what you want to change, create a subroutine and insert a jsr in place of an existing instruction in the original ROM. Be sure to preserve the instruction you replaced! You'll need to put it at the end of your routine, before the rts instruction, so you can preserve the original behavior of the code.

[remowilliams]

Trying to patch and work through an entire game like that must be nuts.   Fixing stuff is hard enough when you have source code.   

The result was worth it though, TC on the Jag is far and away the best version.   

[doctorclu]

I do like Total Carnage actually.  Had a lot of fun playing that with some of my friends over here.

So Songbird, what was it like before you started working on it.  What did you have to change?

[songbird]

The game was essentially a pre-release candidate. So I didn't alter the gameplay, but I did have to fix some basic controls and screens. All of the intro screens had a beta stamp on the bottom which I removed. You could level skip at any time during the game, which I disabled, and I think you could reach the options screen at any time, which I also disabled.

Sounds simple, but trust me, that was a lot of late nights over several months one summer. Disassembling 68K object code and doing the detective work to figure out where the key routines are located is not a fast process.