Fix Debug Mode Crash

(Method #1 by Esrael, Method #2 by Shadow05)

Bug

In Sonic 2, there's a very annoying revolving around Debug Mode. Simply, if you place an object after dying the game will crash. This guide will show you how to fix this.

Esrael's Method

At Debug_SpawnObject: you'll see this

	btst	#button_C,(Ctrl_1_Press).w
	beq.s	Debug_ExitDebugMode
	; Spawn object
	jsr	(SingleObjLoad).l

In between beq.s Debug_ExitDebugMode and ; Spawn object add this,

	cmpi.b	#6,(MainCharacter+status).w	; is Sonic dead?
	bne.s	+				; if not, branch
	rts					; return to prevent Sonic from placing objects.
+

Shadow05's Method

At BuildSprites_ObjLoop: you'll see this.

    if gameRevision=0
	; the additional check prevents a crash triggered by placing an object in debug mode while dead
	; unfortunately, the code it branches *to* causes a crash of its own
	tst.b	id(a0)			; is this object slot occupied?
	beq.w	BuildSprites_Unknown	; if not, branch
	tst.l	mappings(a0)		; does this object have any mappings?
	beq.w	BuildSprites_Unknown	; if not, branch
    else
	; REV01 uses a better branch, but removed the useful check
	tst.b	id(a0)			; is this object slot occupied?
	beq.w	BuildSprites_NextObj	; if not, check next one
    endif

Replace it with this.

	tst.b	id(a0)			; is this object slot occupied?
	beq.w	BuildSprites_NextObj	; if not, check next one
	tst.l	mappings(a0)		; does this object have any mappings?
	beq.w	BuildSprites_NextObj	; if not, check next one

Explanation

The crash occurs because of this line.

	move.w	(1).w,d0

This was a simple "JmpTo" command in the Simon Wai Prototype, but for some reason, this mystery line was added. This causes the Genesis to try to read off an odd-address, as the Genesis can't the game crashes immediately. REV01 tried to fix this by changing the branch to something better, however it removes a useful check still causing the game to crash. Esrael's fix makes Debug Mode check if the player has died while Shadow05's checks if the object has any mappings.

|Fix Debug Mode Crash]]