Saturn decompilation

Internals

Overlays

File Name	Stage
STAGE_00.PRG	Final Stage: Bloodlines
STAGE_0X.PRG	Entrance (1st visit)
STAGE_01.PRG	Entrance (2nd visit)
STAGE_02.PRG	Alchemy Laboratory
STAGE_03.PRG	Marble Gallery
STAGE_04.PRG	Outer Wall
STAGE_14.PRG	Center / Maria Boss
STAGE_15.PRG	Underground Garden / Skeleton Leader
STAGE_16.PRG	Cursed Prison
BOSS_02.PRG	Slogra & Gaibon
LOGO.PRG	Intro copyright logo
TITLE.PRG	Title screen and main menu

Memory mapping (Alucard)

Address	End addr.	Memory Area	File name	Description
06004080	~060505df	High Work Ram	0.BIN	A mix of SEGA libraries and some DRA.BIN
06066000	~0608008b	High Work Ram	GAME.PRG	Similar to DRA.BIN
060A5000		High Work Ram	ALUCARD.PRG	Alucard code overlay
060CF000	~060d5fff	High Work Ram	T_BAT.PRG etc.	Familiar code overlay

Memory mapping (Richter/Maria)

Address	End addr.	Memory Area	File name	Description
00232000		Low Work Ram	RICHTER.CHR/MARIA.CHR	Secondary player sprite graphics
06004080		High Work Ram	0.BIN	Entry point, Sega libraries
06060000		High Work Ram	GAME.PRG	Probably the equivalent of DRA.BIN
060A5000		High Work Ram	RICHTER.PRG/MARIA.PRG	Secondary player code overlay
060DC000		High Work Ram	STAGE_XX.PRG	Stage code overlay
05C1D980		VDP1 Ram	RIC_W.CHR/MAR_W.CHR	Secondary player sprite graphics
05C2F820		VDP1 Ram	STAGE_XX.CHR	Stage sprite graphics

Scratches

0.BIN

Saturn Func	PSX Func	Scratch	Matched?	Note
f_0000ae08	ratan2	https://decomp.me/scratch/889Ky

GAME.PRG

Saturn Func	PSX Func	Scratch	Matched?	Note
f_0000921C	func_800FD4C0	https://decomp.me/scratch/1CORM
f_000092C0	func_800FD5BC	https://decomp.me/scratch/DFpq8		Probably matching
f_00009328	func_800FD664	https://decomp.me/scratch/WEMRF
f_000152f4	Random	https://decomp.me/scratch/F5nPH
f_000157b4	CheckCollision	https://decomp.me/scratch/GZerS
f_0606F798	LearnSpell		y
f_0606F800	func_800FDD44		y
f_0606FC60	IsRelicActive		y
f_060A80E0	func_8011203C		y

ALUCARD.PRG

Saturn Func	PSX Func	Scratch	Matched?	Note
f_060A7DE8	BatFormFinished		y
f_060AA23C	ControlBatForm		y
f_060AC574			y	Part of EntityAlucard

T_BAT.PRG

Saturn Func	PSX Func	Scratch	Matched?	Note
data_00000000	g_ServantDesc	https://decomp.me/scratch/Eex58	Y
func_00000294	func_801713C8	https://decomp.me/scratch/FeLXE
func_000021b8	func_80173E78	https://decomp.me/scratch/kMCmY	Y
func_00002224	func_80173F30	https://decomp.me/scratch/ccc2s		Should be equivalent
func_060D11DC	func_80173EB0	https://decomp.me/scratch/z4bWL
func_060D125C	func_80173F74	https://decomp.me/scratch/nVmi2
func_0000225C	func_80173F74	https://decomp.me/scratch/ha1kO
func_000022AC	func_80173FE8	https://decomp.me/scratch/vOfP4	Y

STAGE_02.PRG (Alchemy Lab)

Saturn Func	PSX Func	Scratch	Matched?	Note
func_060EAFAC	EntityBloodyZombie	https://decomp.me/scratch/ZvlTe

Compiler patterns

Function return values

If you have an issue like this with jsr @r1 vs jsr @r0, your function prototype generally needs to return void to get r1, and non-void to get r0.

void DestroyEntity(Entity*);

  10:    mov.l   50 ,r1           
  12:    jsr     @r1

s32 DestroyEntity(Entity*);

r 10:    mov.l   50 ,r0         
r 12:    jsr     @r0

Equivalent code that produces different asm

The following two functions produce different asm. https://decomp.me/scratch/oNzR9

bool func_06013320(void) {
    if (DAT_060644C0 == 2) {
        return 1;
    }
    return 0;
}

bool func_06013320(void) { return DAT_060644C0 == 2; }

Ghidra output patterns:

Struct pointer dereference:

*(undefined *)(param_1 + 0x11) = 10;

param_1->unk11 = 10;

Graphics Info

Tile graphics are loaded by func_6008588. NOPing this out shows that the tilemap is present but the graphics aren't:

WIP https://decomp.me/scratch/TXaHJ

Part of the Richter sprite graphics are loaded by func_600A490. I think there's two banks loaded to different RAM areas. NOPing this out removes one of the banks.

Tile maps and collision data seem to be loaded by func_606C774. NOPing this out gives the following showing that the tile graphics are loaded but the map is messed up.

These functions all call func_0600f96C which is responsible for writing to an area of Low WRAM around ~26a750.

This area gets read by instructions at 0x60088BC (func_0600871C) or 0x60099fe (func_060098F0) or 0x6009bee (func_06009AE8). which transfers it to a buffer starting at high WRAM 0x0605C120.

NOPing out func_060098F0 prevents part of the transfer to high WRAM and you get this:

NOPing out func_06009AE8 gets this:

Then 0x0605C120 is processed and transferred to VDP2 Ram by func_60098F0. The instruction that does the write is at 0x6009a04.