Genesis Plus is an emulator of the Sega Genesis / Sega Megadrive. This is a port of Charles MacDonald’s Genesis Plus to the GameCube, with a lot of improvements.

Changes:

Core/Sound
completely rewrote sound processing/mixing: sound chips are now clocked with exact output framerate
to ensure 100% smooth video & audio playback, with no lag or skipping, while rendering an accurate number of samples per frame and keeping PSG & FM chips in sync.
improved PSG & FM chips synchronization with CPU execution (fixed point precision).
improved YM2612 core general accuracy (SSG-EG, CSM mode,…) (based upon Nemesis recent tests on real hardware)
improved YM2612 LFO emulation accuracy: fixes “Spider-Man & Venom : Separation Anxiety” (intro)
fixed YM2612 bug with Timer B: fixes “Langrisser Hikari II”/”Der Langrisser II” (Sega logo)
fixed YM2612 context saving/loading.
fixed YM2612 state on reset.
removed outdated & less accurate Gens YM2612 core
added configurable YM2612 DAC resolution emulation.
added configurable & faster FIR resampler (thanks to Blargg & AamirM), removed libsamplerate support.
added configurable Low-Pass filtering
added configurable 3-Band Equalizer (thanks to Neil C).
added an option to boost SN76489 Noise Channel.
adjusted SN76489 cut-off frequency.
implemented Blargg’s blip buffer in SN76489 core (all channels are now lineary interpolated)

Core/VDP
added support for CRAM writes during horizontal blanking (Striker, Zero the Kamikaze Squirrel,…)
added support for 2-Cell vertical scrolling in Interlaced 2 mode
added support for some undocumented mode register bits
added proper emulation of HV Counter latch: fixes Sunset Riders intro
added pixel-accurate emulation of mid-line display on/off (Nigel Mansell World Championship PAL, Ren & Stimpy’s Invention PAL,…)
improved 2-cell vscroll emulation accuracy, as verified on real hardware (Gynoug, Cutie Suzuki no Ringside Angel, Formula One, Kawasaki Superbike Challenge)
improved FIFO timings accuracy: fixes Sol Deace intro
improved sprite masking accuracy (thanks to Nemesis for his test program)
improved sprites processing accuracy: fixes (un)masked sprites in Mickey Mania (3D level), Sonic 2 (VS mode).
improved HBLANK flag timing accuracy: fixes Mega Turrican (Sky level)
improved horizontal blanking & HINT/VINT occurence timing accuracy, as measured on real hardware.
improved HCounter accuracy in 40-cell mode, as measured on real hardware.
improved color accuracy in VDP highlight mode to match results observed on real hardware

Core/CPU
updated Z80 core to last version (fixes interrupt Mode 0 timing and some BIT instructions).
fixed some Z80 instructions timing.
fixed state of Z80 registers on reset (sound issues with Defender & Defender 2 in Williams Arcade Classics)
improved Z80 interrupt accuracy
improved 68k accuracy (initial Reset timing + auto-vectored interrupts handling).
improved 68k timing accuracy for DIVU/DVIS (thanks to Jorge Cwik) & MULU/MULS instructions.
implemented 68k undocumented flags behavior for DIVU/DIVS instructions (Bloodshot / Battle Frenzy)
improved Z80 & 68k cpu execution/synchronization accuracy by using Master Clock as common reference (now run exactly 3420 M-Cycles per line).
modified Z80 & 68k cores to directly use external cycle count instead of intermediate counters.

Core/Extra
added Game Genie hardware emulation.
added Action Replay & Pro Action Replay hardware emulation (only preliminary Pro Action Replay 2 support).
added Sonic & Knuckles “Lock-On” support.
added Cartridge “Hot Swap” feature.
added missing EEPROM support in more games.
added VDP lock-out emulation (TMSS).
improved emulation of copy-protection hardware found in some unlicensed cartridges (Mulan, Pocket Monsters II).
fixed Realtec mapper emulation: fixes missing sound in Balloon Boy / Funny World.
fixed lightgun auto-detection: fixes default cursor position in Lethal Enforcers II.
enabled simultaneous use of multitap & J-CART (Super Skidmarks 6-player mode)
lots of code cleanup, bugfixes & optimization.

Gamecube/Wii
implemented custom FONT engine (uses internal IPL font & GX hardware rendering).
implemented custom GUI engine (uses GX hardware rendering & multithreading)
implemented advanced menu interface (IR pointing, game snapshots, cheats & saves manager, visual & sound effects, BGM support, etc).
improved audio/video synchronization to ensure 100% smooth video & audio playback.
improved soft-reset button support, now works more like real Mega Drive / Genesis (model 1) reset button.
improved lightgun cursors layout.
added automatic ROM loading feature (last played game launches immediately when starting the emulator)
added PAR codes and .pat files support
fixed lot of stability issues and potential memory leaks.

Wii specific
added Video Hardware “Gamma” control
added Video Hardware “Trap Filter” control
improved Mouse emulation through Wii remote
compiled with devkitPPC r22 & libOGC 1.8.5 (includes SDHC & USB2 support through IOS58, removes DVDX support)

http://code.google.com/p/genplus-gx/