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SCHG How-to

Sonic 2 (Simon Wai Prototype) Level Select in Sonic 1

From Sonic Retro

(Original guide by Kram1024)

You probably wonder why Sonic 2 Beta has that level select that looks almost like the Sonic 1 level select, and how Sonic 2 Nick Arcade prototype has one that is the Sonic 1 level select. Well, that is what we are going to make the one in Sonic 1 behave like.

Overview

First, let's look at an overview of what our level select code looks like normally in Sonic 1 (this is from the Hivebrain disassembly):

; ---------------------------------------------------------------------------
; Level	Select
; ---------------------------------------------------------------------------

LevelSelect:
		move.b	#4,($FFFFF62A).w
		bsr.w	DelayProgram
		bsr.w	LevSelControls
		bsr.w	RunPLC_RAM
		tst.l	($FFFFF680).w
		bne.s	LevelSelect
		andi.b	#$F0,($FFFFF605).w ; is	A, B, C, or Start pressed?
		beq.s	LevelSelect	; if not, branch
		move.w	($FFFFFF82).w,d0
		cmpi.w	#$14,d0		; have you selected item $14 (sound test)?
		bne.s	LevSel_Level_SS	; if not, go to	Level/SS subroutine
		move.w	($FFFFFF84).w,d0
		addi.w	#$80,d0
		tst.b	($FFFFFFE3).w	; is Japanese Credits cheat on?
		beq.s	LevSel_NoCheat	; if not, branch
		cmpi.w	#$9F,d0		; is sound $9F being played?
		beq.s	LevSel_Ending	; if yes, branch
		cmpi.w	#$9E,d0		; is sound $9E being played?
		beq.s	LevSel_Credits	; if yes, branch

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

LevSel_PlaySnd:
		bsr.w	PlaySound_Special
		bra.s	LevelSelect
; ===========================================================================

LevSel_Ending:				; XREF: LevelSelect
		move.b	#$18,($FFFFF600).w ; set screen	mode to	$18 (Ending)
		move.w	#$600,($FFFFFE10).w ; set level	to 0600	(Ending)
		rts	
; ===========================================================================

LevSel_Credits:				; XREF: LevelSelect
		move.b	#$1C,($FFFFF600).w ; set screen	mode to	$1C (Credits)
		move.b	#$91,d0
		bsr.w	PlaySound_Special ; play credits music
		move.w	#0,($FFFFFFF4).w
		rts	
; ===========================================================================

LevSel_Level_SS:			; XREF: LevelSelect
		add.w	d0,d0
		move.w	LSelectPointers(pc,d0.w),d0 ; load level number
		bmi.w	LevelSelect
		cmpi.w	#$700,d0	; check	if level is 0700 (Special Stage)
		bne.s	LevSel_Level	; if not, branch
		move.b	#$10,($FFFFF600).w ; set screen	mode to	$10 (Special Stage)
		clr.w	($FFFFFE10).w	; clear	level
		move.b	#3,($FFFFFE12).w ; set lives to	3
		moveq	#0,d0
		move.w	d0,($FFFFFE20).w ; clear rings
		move.l	d0,($FFFFFE22).w ; clear time
		move.l	d0,($FFFFFE26).w ; clear score
		rts	
; ===========================================================================

LevSel_Level:				; XREF: LevSel_Level_SS
		andi.w	#$3FFF,d0
		move.w	d0,($FFFFFE10).w ; set level number

PlayLevel:				; XREF: ROM:00003246�j ...
		move.b	#$C,($FFFFF600).w ; set	screen mode to $0C (level)
		move.b	#3,($FFFFFE12).w ; set lives to	3
		moveq	#0,d0
		move.w	d0,($FFFFFE20).w ; clear rings
		move.l	d0,($FFFFFE22).w ; clear time
		move.l	d0,($FFFFFE26).w ; clear score
		move.b	d0,($FFFFFE16).w ; clear special stage number
		move.b	d0,($FFFFFE57).w ; clear emeralds
		move.l	d0,($FFFFFE58).w ; clear emeralds
		move.l	d0,($FFFFFE5C).w ; clear emeralds
		move.b	d0,($FFFFFE18).w ; clear continues
		move.b	#$E0,d0
		bsr.w	PlaySound_Special ; fade out music
		rts	
; ===========================================================================
; ---------------------------------------------------------------------------
; Level	select - level pointers
; ---------------------------------------------------------------------------
LSelectPointers:
		binclude	misc\ls_point.bin
		align 2
; ---------------------------------------------------------------------------
; Level	select codes
; ---------------------------------------------------------------------------
LevelSelectCode_J:
		binclude	misc\ls_jcode.bin
		align 2

LevelSelectCode_US:
		binclude	misc\ls_ucode.bin
		align 2
; ===========================================================================

Notice anything here?

Button Fix, Part 1

A lot of stuff here we really do not need, as well as the fact that all buttons that are not the D-Pad seem to be used to play a sound or select a level. Let's fix that.

LevelSelect:
		move.b	#4,($FFFFF62A).w
		bsr.w	DelayProgram
		bsr.w	LevSelControls
		bsr.w	RunPLC_RAM
		tst.l	($FFFFF680).w
		bne.s	LevelSelect
		andi.b	#$F0,($FFFFF605).w ; is	A, B, C, or Start pressed?
		beq.s	LevelSelect	; if not, branch
		move.w	($FFFFFF82).w,d0
		cmpi.w	#$14,d0		; have you selected item $14 (sound test)?
		bne.s	LevSel_Level_SS	; if not, go to	Level/SS subroutine
		move.w	($FFFFFF84).w,d0
		addi.w	#$80,d0
		tst.b	($FFFFFFE3).w	; is Japanese Credits cheat on?
		beq.s	LevSel_NoCheat	; if not, branch
		cmpi.w	#$9F,d0		; is sound $9F being played?
		beq.s	LevSel_Ending	; if yes, branch
		cmpi.w	#$9E,d0		; is sound $9E being played?
		beq.s	LevSel_Credits	; if yes, branch

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

LevSel_PlaySnd:
		bsr.w	PlaySound_Special
		bra.s	LevelSelect

We do not need the Japanese credits code, removed that junk. As for the levels, we want to start them with Start but not exclusively just Start, so an andi would be used there. Also, we want Start to exit back to the Sega screen, and why not some nice music? Only B or C should play something on the sound test.

The results should look like this:

LevelSelect:
		move.b	#4,($FFFFF62A).w
		bsr.w	DelayProgram
		bsr.w	LevSelControls
		bsr.w	RunPLC_RAM
		tst.l	($FFFFF680).w
		bne.s	LevelSelect
		move.w	($FFFFFF82).w,d0
		cmpi.w	#$14,d0		; have you selected item $14 (sound test)?
		bne.s	LevSelLevCheckStart; if not, go to	Level/SS subroutine
		cmpi.b	#$80,($FFFFF605).w ; is	Start pressed?
		beq.s	LevSelStartPress	; if true, branch
		cmpi.b	#$20,($FFFFF605).w ; is	B pressed?
		beq.s	LevSelBCPress	; if not, branch
		cmpi.b	#$10,($FFFFF605).w ; is	C pressed?
		beq.s	LevSelBCPress	; if not, branch
		bra.s	LevelSelect
; ===========================================================================
LevSelLevCheckStart:				; XREF: LevelSelect
		andi.b	#$80,($FFFFF605).w ; is	Start pressed?
		beq.s	LevelSelect	; if not, branch
		bra.s	LevSel_Level_SS

LevSelBCPress:				; XREF: LevelSelect
		move.w	($FFFFFF84).w,d0
		addi.w	#$80,d0
		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

LevSel_PlaySnd:
		bsr.w	PlaySound_Special
		bra.s	LevelSelect
		
LevSelStartPress:				; XREF: LevelSelect
		move.b	#$00,$FFFFF600
		jmp MainGameLoop ;go to sega screen

Level Select Music Fix

That fixes the level select so that it runs levels in a Sonic 2 manner, but it doesn't fix the music. Let's do that now.

Find:

Title_ClrVram:
		move.l	d0,(a6)
		dbf	d1,Title_ClrVram ; fill	VRAM with 0

		bsr.w	LevSelTextLoad

and add under dbf d1,Title_ClrVram ; fill VRAM with 0, these lines:

		move.b  #$81,d0
		jsr PlaySound

replace #$81 with your choice of song.

the result should look like:

Title_ClrVram:
		move.l	d0,(a6)
		dbf	d1,Title_ClrVram ; fill	VRAM with 0
		move.b  #$81,d0
		jsr PlaySound
		bsr.w	LevSelTextLoad

Green Hill Zone music at the level select, how lovely. On the other hand, if you plan on using my Sonic 2 Sound Driver port, try using music number $91 and PlayMusic as opposed to PlaySound.

Button Fix, Part 2

As you already know, A is not yet fixed, time to fix that button:

First, we will have to edit the "LevSel_SndTest" routine. $C (left and right) will not work for detecting A. We will need $4C (A/Left/Right) instead, so look in our function for:

LevSel_SndTest:				; XREF: LevSelControls
		cmpi.w	#$14,($FFFFFF82).w ; is	item $14 selected?
		bne.s	LevSel_NoMove	; if not, branch
		move.b	($FFFFF605).w,d1
		andi.b	#$C,d1		; is left/right	pressed?

and change it to read out:

LevSel_SndTest:				; XREF: LevSelControls
		cmpi.w	#$14,($FFFFFF82).w ; is	item $14 selected?
		bne.s	LevSel_NoMove	; if not, branch
		move.b	($FFFFF605).w,d1
		andi.b	#$4C,d1		; is left/right/A pressed?

instead.

Now we can start working on adding the routine to handle A and increase the 16's ($10) part of the sound test:

locate:

		beq.s	LevSel_NoMove	; if not, branch
		move.w	($FFFFFF84).w,d0

and add below:

		btst	#6,d1		; is A pressed?
		bne.s	LevSel_A	; if not, branch

Now locate:

		bcc.s	LevSel_Right
		moveq	#$4F,d0		; if sound test	moves below 0, set to $4F

and add this routine under it to add A support to the level select:

LevSel_A:
		btst	#6,d1		; is A button pressed?
		beq.s	LevSel_Right	; if not, branch
		add.w	#16,d0		; add $10 to sound test

Now the Sonic 1 level select will behave exactly like that of the one in Sonic 2 (Simon Wai prototype, except for night mode and split screen, those can be added manually if you get such a system working). Enjoy your alternative level select :)

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)