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SCHG How-to

Expand the music index to start at $00 instead of $80 (Sonic 2 Clone Driver version)

From Sonic Retro

(Original guide by Mikel, based on a guide by HPZMan)

Notes:

  • Firstly, credit to HPZMan for the original guide he made for Sonic 1.
  • Secondly, you need to have the Sonic 2 Clone Driver in your hack. To get the Clone Driver, go to
    Sonic Retro
    this topic
    ; it requires the Sonic 1 Sound Driver to be ported to your Sonic 2 hack first.

First, go to "PlayMusic:"

You will see something like this:

PlayMusic:
;	tst.b	($FFFFFFE0).w
;	bne.s	+
;	move.b	d0,($FFFFFFE0).w
	move.b	d0,($FFFFF00A).w
	rts
+
	move.b	d0,($FFFFF00A).w
	rts

Change it to:

PlayMusic:
        cmpi.b #$7F, d0
        ble.s   ChkSounds00to7F
        jmp     NormalSoundRequest
ChkSounds00to7F:
        cmpi.b #$01, d0
        bge.s   LoadSlots00to7F
        jmp     NormalSoundRequest
LoadSlots00to7F:
        add.b   #$80, d0; Add $80 you get slot that starts in $81            
        move.b #$01, ($FFFFFFFC) .w; $FFFFFC moves $01 you you make sound to driver load secound index
NormalSoundRequest:
        move.b    d0, ($FFFFF00A) .w
        rts

Then, go to "PlaySound:".

You will see something like this:

PlaySound:
	move.b	d0,($FFFFF00B).w
	rts

Change it to:

PlaySound:
        cmpi.b #$7F, d0
        ble.s   ChkSounds00to7F_Special
        jmp     NormalSoundRequest_Special
ChkSounds00to7F_Special:
        cmpi.b #$01, d0
        bge.s   LoadSlots00to7F_Special
        jmp     NormalSoundRequest_Special
LoadSlots00to7F_Special:
        add.b   #$80, d0; Add $80 you get slot that starts in $81            
        move.b #$01, ($FFFFFFFC) .w; $FFFFFC moves $01 you you make sound to driver load secound index
NormalSoundRequest_Special:
        move.b    d0, ($FFFFF00B) .w
        rts

Then, go to "loc_7202C:"

You will see something like this:

loc_7202C:
		jsr	sub_725CA(pc)
		movea.l	(off_719A0).l,a4
		subi.b	#$81,d7
		move.b	(a4,d7.w),$29(a6)
		movea.l	(Go_MusicIndex).l,a4

Change it to:

loc_7202C:
        	jsr    sub_725CA (PC)
        	movea.l    (off_719A0) .l, a4
        	subi.b    #$81, d7
        	move.b    (a4, d7.w), $29 (a6)
        	movea.l    (Go_MusicIndex) .l, a4
        	cmpi.b #$01, ($FFFFFFFC) .w
        	bne.s   NormalIndexLoad
        	movea.l    (Go_MusicIndex_01to1F) .l, a4
NormalIndexLoad:
        	clr.w   ($FFFFFFFC) .w

Then, search for "Go_MusicIndex:"

You will see something like this:

Go_MusicIndex:	dc.l MusicIndex		; XREF: Sound_81to9F

Add this below "Go_MusicIndex:":

Go_MusicIndex_01to1F:	dc.l MusicIndex_01plus

Then, go to "MusicIndex:"

You will see something like this:

MusicIndex:	dc.l Music81, Music82
		dc.l Music83, Music84
		dc.l Music85, Music86
		dc.l Music87, Music88
		dc.l Music89, Music8A
		dc.l Music8B, Music8C
		dc.l Music8D, Music8E
		dc.l Music8F, Music90
		dc.l Music91, Music92
		dc.l Music93, Music94
		dc.l Music95, Music96
		dc.l Music97, Music98
		dc.l Music99, Music9A
		dc.l Music9B, Music9C
		dc.l Music9D, Music9E
		dc.l Music9F

Then, add this below "MusicIndex:"

MusicIndex_01plus:
         	dc.l Music01, Music02

The "dc.l Music01, Music02" is basically an example of what music slots you should use for Slots $01 to any number you want to stop at

Then, go to "Sound_ChkValue:"

You should see something like this:

Sound_ChkValue:				; XREF: sub_71B4C
		moveq	#0,d7
		move.b	9(a6),d7
		beq.w	Sound_E4
		bpl.s	locret_71F8C
		move.b	#$80,9(a6)	; reset	music flag
		cmpi.b  #$E0,d7
		bge.s  Sound_E0plus
Sound_ChkValue_OtherChecks:
		cmpi.b  #$FF,d7
		bge.s Sound_E0toF8
		cmpi.b	#$9F,d7
		ble.w	Sound_81To9F	
		cmpi.b	#$F0,d7
		ble.w	Sound_A0ToCF
		cmpi.b	#$F9,d7
		bge.w	Sound_E0toE4

Change it to:

Sound_ChkValue:            ; XREF: sub_71B4C
        	moveq    #0, d7
        	move.b    9 (a6), d7
      		beq.w    Sound_E4
       		bpl.s    locret_71F8C
        	move.b    #$80,9 (a6); reset    music flag
		cmpi.b  #$E0,d7
		bge.s  Sound_E0plus
        	cmpi.b #$01, ($FFFFFFFC) .w
        	bne.s   Load81to9F
        	jmp     Sound_ChkValueFor00
Load81to9F:
        	cmpi.b    #$9F, d7
      		bls.w    Sound_81to9F; music    $81-$9F
Sound_ChkValue_OtherChecks:
		cmpi.b  #$FF,d7
		bge.s Sound_E0toF8
		cmpi.b	#$F0,d7
		ble.w	Sound_A0ToCF
		cmpi.b	#$F9,d7
		bge.w	Sound_E0toE4

Now, go to "Sound_81to9F:", and change it to this:

Sound_ChkValueFor00:
        	cmpi.b #$FF, d7; $FF = Last slot will be musics in index $00 - $7F ($FF = $7F)
        	bls.w   Sound_81to9F
        	rts


Sound_81to9F:				; XREF: Sound_ChkValue
		cmpi.b	#$98,d7		; is "extra life" music	played?
		bne.s	loc_72024	; if not, branch
		tst.b	$27(a6)
		bne.w	loc_721B6
		lea	$40(a6),a5
		moveq	#9,d0

Finally, we are going to Change the number of sound test slots in the options and level select menus

To change the Options Sound Test,

Go to "word_917A:"

You will see something like this:

	dc.w $7FFF	; 4
	dc.w Sound_test_sound	; 5

Change the "$7" in "$7FFF" to anything you like, like "$FFFF", or "$CFFF"


To change the Level Select Sound Test,

Go to "loc_9522:"

You will see something like this:

loc_9522:
	cmpi.w	#$15,(Level_select_zone).w
	bne.s	loc_958A
	move.w	(Sound_test_sound).w,d0
	move.b	(Ctrl_1_Press).w,d1
	btst	#2,d1
	beq.s	loc_953E
	subq.b	#1,d0
	bcc.s	loc_953E
	moveq	#$7F,d0

On the last moveq Change the "$7" in "$7F,d0" to mach the first two letters in the value you used above, like "$FF", or "$CF".

Go to "loc_954E:"

You will see something like this:

loc_954E:
	btst	#6,d1
	beq.s	loc_955C
	addi.b	#$10,d0
	andi.b	#$7F,d0

As before but on andi.b Change the "$7" in "$7F,d0" to the value you used above, like "$FF", or "$CF".

Lastly, Head back up to "loc_953E:" it should be between the two sections you just changed.

You will see something like this:

loc_953E:
	btst	#3,d1
	beq.s	loc_954E
	addq.b	#1,d0
	cmpi.w	#$80,d0
	bcs.s	loc_954E
	moveq	#0,d0

change it to this:

loc_953E:
	btst	#3,d1
	beq.s	loc_954E
	addq.b	#1,d0

ADDITIONAL NOTES: Level Select Sound Test code was contributed by User:MattATobin with guidance from Ayla and Sik

SCHG How-To Guide: Sonic the Hedgehog 2 (16-bit)
Fixing Bugs
Fix Demo Playback | Fix a Race Condition with Pattern Load Cues | Fix Super Sonic Bugs | Use Correct Height When Roll Jumping | Fix Jump Height Bug When Exiting Water | Fix Spin Dash Code and Add Spin Dash Speeds | Fix Screen Boundary Spin Dash Bug | Correct Drowning Bugs | Fix Camera Y Position for Tails | Fix Tails Subanimation Error | Fix Tails' Respawn Speeds | Fix Accidental Deletion of Scattered Rings | Fix Ring Timers | Fix Rexon Crash | Fix Monitor Collision Bug | Fix EHZ Deformation Bug | Correct CPZ Boss Attack Behavior | Fix Bug in ARZ Boss Arrow's Platform Behavior | Fix ARZ Boss Walking on Air Glitch | Fix ARZ Boss Sprite Behavior | Fix Multiple CNZ Boss Bugs | Fix HTZ Background Scrolling Mountains | Fix OOZ Launcher Speed Up Glitch | Fix DEZ Giant Mech Collision Glitch | Fix Boss Deconstruction Behavior | Fix Speed Bugs
Design Choices
Remove the Air Speed Cap | Disable Floor Collision While Dying | Modify Super Sonic Transformation Methods & Behavior | Enable/Disable Tails in Certain Levels | Collide with Water After Being Hurt | Retain Rings When Returning at a Star Post | Improve the Fade In\Fade Out Progression Routines | Fix Scattered Rings' Underwater Physics | Insert LZ Water Ripple Effect | Restore Lost CPZ Boss Feature | Prevent SCZ Tornado Spin Dash Death | Improve ObjectMove Subroutines | Port S3K Rings Manager | Port S3K Object Manager | Port S3K Priority Manager | Edit Level Order with ASM‎ | Alter Ring Requirements in Special Stages | Make Special Stage Characters Use Normal DPLCs | Speed Up Ring Loss Process | Add beta spindash to Sonic 2 | Change spike behaviour in Sonic 2
Adding Features
Create Insta-kill and High Jump Monitors | Create Clone and Special Stage Monitors | Port Knuckles
Sound Features
Port Sonic 1 Sound Driver | Port Sonic 2 Clone Driver | Port Sonic 3 Sound Driver | Expand the Music Index to Start at $00 (Sonic 2 Clone Driver Version)
Extending the Game
Extend the Level Index Past $10 | Extend the Level Select | Extend Water Tables | Add Extra Characters | Free Up 2 Universal SSTs