4DO and Opera Fix Parity Audit¶

Snapshot: 2026-11-01. This document closes the 4DO/Opera fix-bit inventory and records how each known per-game quirk maps to 5DO.

Sources¶

4DO FourDO/Emulation/GameConsole.cs, Start: the FIX_BIT_* assignments after the game source opens.
4DO FreeDOCore FixMode: the bit values consumed by the ARM/MADAM/CEL paths.
Opera libopera: no per-game fix-bit table. Opera uses generic accuracy models for the behaviors below; its ARM cycle classes, CEL origin, and VDLP code are the reference for the generic replacements.

Mapping¶

4DO bit	Value	4DO IDs	5DO mapping	Status
`FIX_BIT_TIMING_1`	`0x00000001`	`F3AF1B13` Crash 'n Burn (JP), `217344B0` Crash 'n Burn (US)	`FixMode.BitTiming1`	Mapped. LDM value/PC timing.
`FIX_BIT_TIMING_2`	`0x00000002`	`DBB419FA`, `07C32F10`, `5282889F`, `7340307E` (Street Fighter II family)	`FixMode.BitTiming2`	Mapped. Intro sync.
`FIX_BIT_TIMING_3`	`0x00000004`	`CB8EE795` DinoPark Tycoon	`FixMode.BitTiming3`	Mapped. Scale Y * 5.
`FIX_BIT_TIMING_5`	`0x00000010`	`1A370EBA`, `B35C911D` Microcosm	`FixMode.BitTiming5`	Mapped. VDLP current/previous bitmap offsets.
`FIX_BIT_TIMING_6`	`0x00000020`	`0511D3D2`, `9F7D72BC`, `E843C635` Alone in the Dark	`FixMode.None` (generic replacement)	Retired. The generic XYPOSH/XYPOSL CEL origin and literal-row model replaced the title-specific Y step.
`FIX_BIT_GRAPHICS_STEP_Y`	`0x00080000`	`2AABA5B9` Samurai Shodown (EU/US), `BF61BB32` Samurai Shodown (JP)	`FixMode.None` (generic replacement)	Retired. The generic CEL origin model replaced the title-specific Y step.
`FIX_BIT_TIMING_4`	`0x00000008`	none	n/a	Reserved; no 4DO title uses it.
`FIX_BIT_TIMING_7`	`0x00000040`	none	n/a	Reserved; no 4DO title uses it.

GameCompatibilityTests locks every row, including case-insensitive and full-MD5 lookups, unknown IDs, collision behavior, and explicit overrides.

Evidence¶

The comparisons below used run --bios bios/panafz10.bin --frames 3000 --json and the default automatic fix mode unless a --fix-mode value is shown.

Title	Auto fix	Comparison	Result
DinoPark Tycoon (USA)	`0x4`	no fix	Frame hashes differ (`0xA1F3E800` vs `0xF2607174`), confirming the scale-Y fix is active. Both frames render.
Microcosm (USA)	`0x10`	no fix	Identical hash `0x4E6A4651` at the 3,000-frame title scene; the mapping is retained and does not regress the scene.
Super Street Fighter II Turbo (USA)	`0x2`	no fix	Identical hash `0x1FFBE3FA` at 3,000 frames; the intro-sync path is retained for later frames.
Alone in the Dark (USA)	none	forced `0x20`	Identical hash `0x175B8FE4`; the retired timing-6 bit is not needed.
Samurai Shodown (USA, Europe)	none	forced `0x80000`	Identical hash `0x86C04E50`; the retired graphics-step-Y bit is not needed.

The local Alone in the Dark matrix also reaches gameplay and save/load roundtrips, and Super Street Fighter II Turbo plays a full CPU-vs-CPU attract match past 10,000 frames. Those results are recorded in Compatibility.md.

Result¶

Every known 4DO fix bit is either mapped to the matching FixMode value or explicitly replaced by a generic model. There are no unmapped IDs and no silent mismatches. The remaining work is game-database metadata (SYS-17), not fix behavior.