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SCHG How-to

Expand the music index from $94 to $9F

From Sonic Retro

(Original guide by SoullessSentinel)

To add more music slots to the sound test, search for this code in the level select routine:

LevSel_NoCheat:
        cmpi.w    #$94,d0    ; is sound $80-$94 being played?
        bcs.s    LevSel_PlaySnd; if yes, branch
        cmpi.w    #$A0,d0    ; is sound $95-$A0 being played?
        bcs.s    LevelSelect; if yes, branch

Change the line:

        cmpi.w    #$94,d0    ; is sound $80-$94 being played?

So it reads:

        cmpi.w    #$A0,d0    ; is sound $80-$9F being played?

Then rebuild the ROM.

And now the sound test will have the music slots going up to $9F, instead of $94, however attempts to play empty music slots will crash the sound driver, and possibly lock up the emulator. So, make sure you include a song in every slot.

Note: The disassembly's comments are incorrect. The correct ID ranges are $80-$93 and $94-$9F.

SCHG How-To Guide: Sonic the Hedgehog (16-bit)
Fixing Bugs
Fix Demo Playback | Fix a Race Condition with Pattern Load Cues | Fix the SEGA Sound | Display the Press Start Button Text | Fix the Level Select Menu | Fix the Hidden Points Bug | Fix Accidental Deletion of Scattered Rings | Fix Ring Timers | Fix the Walk-Jump Bug | Correct Drowning Bugs | Fix the Death Boundary Bug | Fix the Camera Follow Bug | Fix Song Restoration Bugs | Fix the HUD Blinking | Fix the Level Select Graphics Bug
Changing Design Choices
Change Spike Behavior | Fix Special Stage Jumping Physics | Improve the Fade In\Fade Out Progression Routines | Fix Scattered Rings' Underwater Physics | Remove the Speed Cap | Port the REV01 Background Effects | Port Sonic 2's Level Art Loader | Retain Rings Between Acts | Add Sonic 2 (Simon Wai Prototype) Level Select | Improve ObjectMove Subroutines
Adding Features
Add Spin Dash ( Part 1 / Part 2 / Part 3 / Part 4 ) | Add Eggman Monitor
Sound Features
Expand Music Index From $94 to $9F | Extend Music Slots | Play Different Songs Per Act | Expand Music Index to Start at $00 | Port Sonic 2 Final Sound Driver | Port Sonic 3's Sound Driver
Extending the Game
Load Chunks From ROM | Add Extra Characters | Make an Alternative Title Screen | Use Dynamic Tilesets | Make GHZ Load Alternate Art | Add a New Zone | Set Up the Goggle Monitor | Add New Moves | Add a Dynamic Collision System | Dynamic Special Stage Walls System | Extend Sprite Mappings and Art Limit | Enigma Credits
Miscellaneous
Convert the Hivebrain 2005 Disassembly to ASM68K
Split Disassembly Guides
Set Up a Split Disassembly | Basic Level Editing | Basic Art Editing | Basic ASM Editing (Spin Dash)