Tricky-to-emulate games

This is a list of various emulation bugs encountered during the development of Mesen-S. It is meant as a quick reference to help others find and debug issues with their own emulation core. It can also be used to find games that might be affected by a code change, for regression testing purposes.

Cause	Affected games
Missing/incorrect open bus implementation (CPU or PPU)	Captain America and the Avengers: Broken graphics during gameplay Combatribes, The: Doesn't boot Home Alone: Crashes after main menu Rock n' Roll Racing: Broken graphics in character select Super 3D Noah's Ark: Broken mode 7 graphics
Incorrect or missing BRK/COP implementation	Actraiser: Crashes after menu Bishoujo Senshi Sailor Moon - Another Story: Crashes after menu Cybernator: Intro restarts when starting game Dekitate High School: Doesn't boot Illusion of Gaia: Doesn't boot Kamaitachi no Yoru: Doesn't boot Soul Blazer: Doesn't boot
VRAM writes are not ignored during rendering	Hook: Text glitches during intro
Ignored VRAM writes during rendering are not incrementing the VRAM address	Kick Off
Offset-per-tile wraparound logic is incorrect	Super Famista 5: Issues at the top of the screen during animation inside the main menu
Offset-per-tile implementation has bugs	Axelay: Broken level background in some areas of stage 2 Chrono Trigger: Broken layout in in-game menu
Mode 7 doesn't implement window logic	Atlas, The - Renaissance Voyager: Broken mode 7 graphics during intro MechWarrior: Broken mode 7 graphics during gameplay
Mode 7 scroll offsets are not latched at the beginning of the scanline	NHL '94: Glitch scanline in the middle of screen during intro animation
Color window is not applied to all pixels	Krusty's Super Fun House: Broken graphics at the edges of the screen
Color math for subscreen in high resolution modes is incorrect	Jurassic Park: Broken graphics during gameplay
Implementation of OAM writes during rendering is inaccurate	Uniracers: In 2-player mode, second player's unicycle doesn't display correctly
OAM fetching/rendering timing inaccurate	Mega lo Mania - Jikuu Daisenryaku: A single black line appears in the middle of the screen during the intro
DMA controller power on state is invalid	Heian Fuuunden: Corrupt title screen when pressing start to skip opening animation
CPU doesn't run an extra cycle before starting DMA after write to $420B	Mighty Morphin Power Rangers - The Fighting Edition
DMA controller allows reading B-bus registers using A-bus address	Krusty's Super Fun House: Wrong colors during gameplay
DMA/HDMA timings are inaccurate	Circuit USA: Broken graphics in menu Jumbo Ozaki no Hole in One: Broken graphics in menu
DMA is not suspended when HDMA runs	Dekitate High School
HDMA doesn't ignore "fixed transfer" flag	Batman Forever: Broken mode 7 graphics during intro Lost Vikings, The: Black screen when gameplay starts
HDMA doesn't ignore "decrement" flag	Adventures of Kid Kleets, The: Broken graphics at power on MechWarrior: Broken mode 7 graphics during gameplay
HDMA "do tranfer" flag isn't set/reset properly	Aladdin: Broken graphics in the background on first level Super Ghouls'n Ghosts: Black screen once gameplay starts
V-IRQ doesn't trigger when V-IRQs are enabled for the current scanline	RoboCop versus The Terminator
NMI isn't triggered when NMI is enabled partway through vertical blank	Alien vs Predator: Screen flashes during gameplay Pocky & Rocky: Screen flashes during gameplay
SPC timings are inaccurate (requires SPC to run 1 cycle at a time, rather than 1 instruction at a time)	ActRaiser 2: Freezes Hiouden - Mamono-tachi to no Chikai: Broken sound Illusion of Gaia: Doesn't boot Tales of Phantasia: Missing sound effects, freezes
CPU read effects do not occur early enough in the CPU's cycle	Rendering Ranger R2: Freezes due to infinite loop with SPC
DSP KOF register is not initialized to $00	Chester Cheetah - Too Cool to Fool: Missing sound effects King of Dragons: Missing sound effects
SRAM mappings are incorrect	Fire Emblem - Thracia 776 Ys III - Wanderers from Ys
RAM power on state is "incorrect"	Bishoujo Senshi Sailor Moon - Another Story: Random static in music during intro (when SPC RAM is randomized) Death Brade: Duel ends instantly when RAM is initialized with 0s Power Drive: Broken graphics when RAM is initialized with 0s Super Keiba 2: Blackscreen after a few menus when SRAM is initialized with 0s
Super FX - RPIX implementation is incorrect	Yoshi's Island: Broken effects in tunnels (https://github.com/SourMesen/Mesen-S/issues/25)