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Sega - MS/GG/MD/CD (Genesis Plus GX)

Background

Genesis Plus GX is an open-source Sega 8/16 bit emulator developed by Eke-Eke which focuses on accuracy and portability. The source code, originally based on Genesis Plus 1.3 by Charles MacDonald, has been heavily modified & enhanced, with respect to initial goals and design, in order to improve the accuracy of emulation, implementing new features and adding support for extra peripherals, cartridge & systems hardware such as various lightguns, the FM Sound Unit and Lock-On cartridge technology.

Genesis Plus GX has 100% compatibility with Genesis / Mega Drive, Sega/Mega CD, Master System, Game Gear, SG-1000 & Pico released software (including all unlicensed or pirate known dumps), also emulating backwards compatibility modes when available. Keep in mind that 32X games are not supported.

The Genesis Plus GX core has been authored by

  • Eke-Eke
  • Charles McDonald

The Genesis Plus GX core is licensed under

A summary of the licenses behind RetroArch and its cores can be found here.

BIOS

Required or optional firmware files go in the frontend's system directory.

Please note that BIOS choice isn't locked to any specific revisions.

BIOS files that are labeled (bootrom) and (lock-on) must have their corresponding core option ('System bootrom' core option or 'Cartridge lock-on' core option) configured correctly in order for them to be loaded.

Filename Description md5sum
bios_MD.bin MegaDrive TMSS startup ROM (bootrom) - Optional 45e298905a08f9cfb38fd504cd6dbc84
bios_CD_E.bin MegaCD EU BIOS - Required for MegaCD EU games e66fa1dc5820d254611fdcdba0662372
bios_CD_U.bin SegaCD US BIOS - Required for SegaCD US games 854b9150240a198070150e4566ae1290
bios_CD_J.bin MegaCD JP BIOS - Required for MegaCD JP games 278a9397d192149e84e820ac621a8edd
bios_E.sms MasterSystem EU BIOS (bootrom) - Optional 840481177270d5642a14ca71ee72844c
bios_U.sms MasterSystem US BIOS (bootrom) - Optional 840481177270d5642a14ca71ee72844c
bios_J.sms MasterSystem JP BIOS (bootrom) - Optional 24a519c53f67b00640d0048ef7089105
bios.gg GameGear BIOS (bootrom) - Optional 672e104c3be3a238301aceffc3b23fd6
sk.bin Sonic & Knuckles ROM (lock-on) - Optional 4ea493ea4e9f6c9ebfccbdb15110367e
sk2chip.bin Sonic & Knuckles UPMEM ROM (lock-on) - Optional b4e76e416b887f4e7413ba76fa735f16
areplay.bin Action Replay ROM (lock-on) - Optional a0028b3043f9d59ceeb03da5b073b30d
ggenie.bin Game Genie ROM (lock-on) - Optional e8af7fe115a75c849f6aab3701e7799b

Extensions

Content that can be loaded by the Genesis Plus GX core have the following file extensions:

.m3u
.mdx
.md
.smd
.gen
.bin
.cue
.iso
.chd
.bms
.sms
.gg
.sg
.68k
.sgd

RetroArch database(s) that are associated with the Genesis Plus GX core:

Features

Frontend-level settings or features that the Genesis Plus GX core respects.

Feature Supported
Restart ✔
Saves ✔
States ✔
Rewind ✔
Netplay ✔
Core Options ✔
RetroAchievements ✔
RetroArch Cheats ✔
Native Cheats ✕
Controls ✔
Remapping ✔
Multi-Mouse ✔
Rumble ✕
Sensors ✕
Camera ✕
Location ✕
Subsystem ✕
Softpatching ✕
Disk Control ✔
Username ✕
Language ✕
Crop Overscan ✕
LEDs ✕

Directories

The Genesis Plus GX core's library name is 'Genesis Plus GX'

The Genesis Plus GX core saves/loads to/from these directories.

Frontend's Save directory

File Description
*.srm MS/GG/MD/Pico/SG-1000 Cartridge backup save
cart.brm Sega/Mega CD RAM Cart
scd_U.brm Sega CD US Backup RAM - When the 'CD System BRAM' core option is set to per bios
scd_E.brm Mega CD EU Backup RAM - When the 'CD System BRAM' core option is set to per bios
scd_J.brm Mega CD JP Backup RAM - When the 'CD System BRAM' core option is set to per bios
*.brm Sega CD/MegaCD Backup RAM - When the 'CD System BRAM' core option is set to per game

Frontend's State directory

File Description
*.state# State

Geometry and timing

  • The Genesis Plus GX core's core provided FPS is dependent on the loaded content.
  • The Genesis Plus GX core's core provided sample rate is 44100 Hz
  • The Genesis Plus GX core's base width is dependent on the loaded content.
  • The Genesis Plus GX core's base height is dependent on the loaded content.
  • The Genesis Plus GX core's max width is 720
  • The Genesis Plus GX core's max height is 576
  • The Genesis Plus GX core's core provided aspect ratio is dependent on the 'Core-provided aspect ratio' core option.

Loading Sega CD games

When loading Sega CD games, Genesis Plus GX needs a cue-sheet that points to an image file. A cue sheet, or cue file, is a metadata file which describes how the tracks of a CD or DVD are laid out.

If you have e.g. foo.bin, you should create a text file and save it as foo.cue. If the Sega CD game is single-track, the cue file contents should look like this:

 FILE "foo.bin" BINARY
  TRACK 01 MODE1/2352
   INDEX 01 00:00:00

After that, you can load the foo.cue file in RetroArch with the Genesis Plus GX core.

Certain Sega CD games are multi-track, so their .cue files might be more complicated.

Here's a cue file example done with Lunar - Eternal Blue (USA)

For Sega-CD games, ISO + WAV, BIN + CUE and ISO + OGG formats are supported; ISO + MP3 is not supported. Audio files must be in the 16-bit stereo 44100Hz format. If using a cue sheet, WAV or OGG tracks should be denoted as AUDIO.

When loading ISO + WAV or ISO + OGG format games, the core will attempt to load a cue named the same as the iso first. If one is not found, the following audio track naming formats are accepted for a data track of "game.iso":

  • game02.ogg
  • game 02.ogg
  • game-02.ogg
  • game - 02.ogg
  • game_02.ogg

Core options

The Genesis Plus GX core has the following option(s) that can be tweaked from the core options menu. The default setting is bolded.

Settings with (Restart) means that core has to be closed for the new setting to be applied on next launch.

  • System hardware [genesis_plus_gx_system_hw] (auto/sg-1000/sg-1000 II/mark-III/master system/master system II/game gear/mega drive / genesis)

    Choose which system is going to be emulated.

  • System region [genesis_plus_gx_region_detect] (auto/ntsc-u/pal/ntsc-j)

    Choose which region the system is from.

  • System lockups [genesis_plus_gx_force_dtack] (enabled/disabled)

    Emulate system lockups that occur on real hardware.

  • System bootrom [genesis_plus_gx_bios] (disabled/enabled)

    Runs bootrom if available and then starts loaded content after the boot sequence. Look above at the BIOS section for more information.

  • CD System BRAM [genesis_plus_gx_bram] (per bios/per game)

    The Sega CD's internal memory cannot hold a lot of saves. Setting this core option to per game allows each game to have its own one brm file, thus negating any lack of available space issues.

CD System BRAM diagram

  • 68k address error [genesis_plus_gx_addr_error] (enabled/disabled)

    Emulate the 68k address error that occurs on real hardware. Set this to disabled when playing rom hacks since most emulators used to develop rom hacks don't emulate the error.

  • Cartridge lock-on [genesis_plus_gx_lock_on] (disabled/game genie/action replay (pro)/sonic & knuckles)

    Select a lock-on cartridge. Look above at the BIOS section for more information.

  • Master System FM (YM2413) [genesis_plus_gx_ym2413] (auto/disabled/enabled)

    Enable the Master System FM chip. (Enhanced sound output support for SMS compatible games)

  • Mega Drive / Genesis FM [genesis_plus_gx_ym2612] (mame (ym2612)/mame (asic ym3438)/mame (enhanced ym3438)/nuked (ym2612)/nuked (asic ym3438)/nuked (discrete ym3438))

    Awaiting description.

  • Sound output [genesis_plus_gx_sound_output] (stereo/mono)

    Self-explanatory.

  • Audio filter [genesis_plus_gx_audio_filter] (disabled/low-pass)

    Awaiting description.

  • Low-pass filter % [genesis_plus_gx_lowpass_range] (5 to 95 in increments of 5. 60 is default)

    Awaiting description.

  • Blargg NTSC filter [genesis_plus_gx_blargg_ntsc_filter] (Off/monochrome/composite/svidio/rgb)

    Self-explanatory.

Blargg NTSC filter - Off

Blargg NTSC filter - monochrome

Blargg NTSC filter - composite

Blargg NTSC filter - svideo

Blargg NTSC filter - rgb

  • LCD Ghosting filter [genesis_plus_gx_lcd_filter] (disabled/enabled)
LCD Ghosting filter - On

  • Borders [genesis_plus_gx_overscan] (disabled/top/bottom/left/right/full)

    Self-explanatory.

  • Game Gear extended screen [genesis_plus_gx_gg_extra] (disabled/enabled)

    Self-explanatory.

Game Gear extended screen - Off

Game Gear extended screen - On

  • Core-provided aspect ratio [genesis_plus_gx_aspect_ratio] (auto/NTSC PAR/PAL PAR)

    Choose the Core-provided aspect ratio. RetroArch's aspect ratio must be set to Core provided in the Video settings for this to function properly.

  • Interlaced mode 2 output [genesis_plus_gx_render] (single field/double field)

    Change how interlaced mode 2 output is handled. Games like Sonic 2's multiplayer mode uses Interlaced Mode 2.

Interlaced mode 2 output - single field

Interlaced mode 2 output - double field

  • Show Lightgun crosshair [genesis_plus_gx_gun_cursor] (disabled/enabled)

    Shows lightgun crosshairs for the 'MD Menacer', 'MD Justifiers', and 'MS Light Phaser' Device Types.

Lightgun crosshair

  • Invert Mouse Y-axis [genesis_plus_gx_invert_mouse] (disabled/enabled)

    Inverts the Mouse Y-axis for the 'MD Mouse' Device Type.

  • CPU speed [genesis_plus_gx_overclock] (100%/125%/150%/175%/200%)

    Overclock the emulated CPU.

  • Remove per-line sprite limit [genesis_plus_gx_no_sprite_limit] (disabled/enabled)

    Reduce sprite flickering when enabled.

User 1 device types

The Genesis Plus GX core supports the following device type(s) in the controls menu, bolded device types are the default for the specified user(s):

User 2 device types

Other devices

  • PICO tablet - The Genesis Plus GX core can emulate PICO tablet inputs but this is done automatically, based off the game's CRC, and cannot be manually selected as a device type.
  • Terebi Oekaki tablet - The Genesis Plus GX core can emulate Terebi Oekaki table inputs but this is done automatically, based off the game's CRC, and cannot be manually selected a device type.

Multitap

Activating multitap support in compatible games can be configured by the 4-WayPlay, Teamplayer, Master Tap device types for the corresponding users.

Joypad

RetroPad Inputs User 1 - 8 input descriptors MD Joypad 3 Button MD Joypad 6 Button MS Joypad 2 Button MS Paddle Control MS Sports Pad MD XE-1AP
B B B 1 1 1 E2
A A A E1
Mode Mode Select
Start Start Start Start Start Start Start
D-Pad Up D-Pad Up D-Pad Up D-Pad Up
D-Pad Down D-Pad Down D-Pad Down D-Pad Down
D-Pad Left D-Pad Left D-Pad Left D-Pad Left
D-Pad Right D-Pad Right D-Pad Right D-Pad Right
C C C 2 2
Y Y
X X C
Z Z A
D
B
X Paddle Trackball X Thumb-stick X
Y Trackball Y Thumb-stick Y
X Slider Y
Y Slider X

Mouse

RetroMouse Inputs MD Mouse
Mouse Cursor MD Mouse Cursor
Mouse 1 MD Mouse Left
Mouse 2 MD Mouse Right
Mouse 3 MD Mouse Start
Wheel Down MD Mouse Center

Pointer

RetroPointer Inputs MS Graphic Board
or Pointer Position MS Graphic Board Stylus
Mouse 1 MS Graphic Board Pen
Mouse 2 MS Graphic Board Menu
Mouse 3 MS Graphic Do

Lightgun

RetroLightgun Inputs MD Menacer MD Justifier MS Light Phaser
Gun Crosshair MD Menacer Crosshair MD Justifier Crosshair MS Light Phaser Crosshair
Gun Trigger MD Menacer A MD Justifier A MS Light Phaser A
Gun Aux A MD Menacer B MD Justifer B MS Light Phaser B
Gun Aux B MD Menacer C MD Justifer C MS Light Phaser C
Gun Start MD Menacer Start MD Justifer Start MS Light Phaser Start

Other

Inputs PICO tablet Terebi Oekaki tablet
or Pointer Position PICO tablet Stylus Terebi Oeka tablet Stylus
Mouse 1 PICO tablet Pen Terebi Oeka tablet Pen
Mouse 2 PICO tablet Red
Mouse 3 Terebo Peka tablet Start
Wheel Up PICO tablet Previous page
Wheel Down PICO tablet Next page
PICO tablet Up (White)
PICO tablet Down (Orange)
PICO tablet Left (Purple)
PICO tablet Right (Green)

Sega 16-bit

Last update: 2023-03-16