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# Sega Genesis/MegaDrive Documentation

Last updated January 2, 2024
Valid as of 1.32.0-UNSTABLE

Table of Contents:

- Introduction
- Settings Reference

## Introduction

Mednafen's Sega Genesis/Megadrive emulation is based off of Genesis Plus and information and code from Genesis Plus GX(old GPL-licensed version). The GPL-incompatible CPU and sound emulation cores in the aforementioned projects have been replaced with GPLed or GPL-compatible alternatives; heavily-modified and improved YM2612 emulation from Gens, and Z80 emulation core from FUSE.

Sega Genesis/Megadrive emulation should still be considered experimental; there are still likely timing bugs in the 68K emulation code, the YM2612 emulation code is not particularly accurate, and the VDP code has timing-related issues.

Sega 32X and Sega CD are not currently supported, though there is a bit of stub Sega CD code present currently.

## Settings Reference

Caution: Any settings that change emulation behavior as seen from the emulated game are shown with the setting name bolded in the table. One should be conscious of these settings if one has changed them from the default values when using network play or movies, as they can cause desychronizations if not set the same among hosts(or between the recording emulator and the playing emulator).

Setting: | Value Type: | Possible Values: | Default Value: | Description:
--- | --- | --- | --- | ---
md.cdbios | string |  | us_scd1_9210.bin | Path to the CD BIOS SegaCD/MegaCD emulation is currently nonfunctional.
md.correct_aspect | boolean | 0 1 | 1 | Correct the aspect ratio.
md.input.auto | boolean | 0 1 | 1 | Automatically select appropriate input devices. Automatically select appropriate input devices, based on an internal database. Currently, only multitap device usage data is contained in the database.
md.input.mouse_sensitivity | real | through | 1.00 | Emulated mouse sensitivity.

md.input.multitap

enum

none
tp1
tp2
tpd
4way

none

Enable multitap(s).

- none - No multitap(s).
- tp1 - Team Player/Sega Tap on MD/Genesis port 1.
- tp2 - Team Player/Sega Tap on MD/Genesis port 2.
- tpd - Team Player/Sega Tap on both MD/Genesis ports.
- 4way - EA 4-Way Play

md.input.port1

enum

none
gamepad2
gamepad
gamepad6
megamouse

gamepad

Input device for Virtual Port 1

- none - none
- gamepad2 - 2-Button Gamepad
- gamepad - 3-Button Gamepad
- gamepad6 - 6-Button Gamepad
- megamouse - Sega Mega Mouse

md.input.port2

enum

none
gamepad2
gamepad
gamepad6
megamouse

gamepad

Input device for Virtual Port 2

- none - none
- gamepad2 - 2-Button Gamepad
- gamepad - 3-Button Gamepad
- gamepad6 - 6-Button Gamepad
- megamouse - Sega Mega Mouse

md.input.port3

enum

none
gamepad2
gamepad
gamepad6
megamouse

gamepad

Input device for Virtual Port 3

- none - none
- gamepad2 - 2-Button Gamepad
- gamepad - 3-Button Gamepad
- gamepad6 - 6-Button Gamepad
- megamouse - Sega Mega Mouse

md.input.port4

enum

none
gamepad2
gamepad
gamepad6
megamouse

gamepad

Input device for Virtual Port 4

- none - none
- gamepad2 - 2-Button Gamepad
- gamepad - 3-Button Gamepad
- gamepad6 - 6-Button Gamepad
- megamouse - Sega Mega Mouse

md.input.port5

enum

none
gamepad2
gamepad
gamepad6
megamouse

gamepad

Input device for Virtual Port 5

- none - none
- gamepad2 - 2-Button Gamepad
- gamepad - 3-Button Gamepad
- gamepad6 - 6-Button Gamepad
- megamouse - Sega Mega Mouse

md.input.port6

enum

none
gamepad2
gamepad
gamepad6
megamouse

gamepad

Input device for Virtual Port 6

- none - none
- gamepad2 - 2-Button Gamepad
- gamepad - 3-Button Gamepad
- gamepad6 - 6-Button Gamepad
- megamouse - Sega Mega Mouse

md.input.port7

enum

none
gamepad2
gamepad
gamepad6
megamouse

gamepad

Input device for Virtual Port 7

- none - none
- gamepad2 - 2-Button Gamepad
- gamepad - 3-Button Gamepad
- gamepad6 - 6-Button Gamepad
- megamouse - Sega Mega Mouse

md.input.port8

enum

none
gamepad2
gamepad
gamepad6
megamouse

gamepad

Input device for Virtual Port 8

- none - none
- gamepad2 - 2-Button Gamepad
- gamepad - 3-Button Gamepad
- gamepad6 - 6-Button Gamepad
- megamouse - Sega Mega Mouse

md.region

enum

game
overseas_ntsc
overseas_pal
domestic_ntsc
domestic_pal

game

Emulate the specified region's Genesis/MegaDrive

- game - Match game's header.
  Emulate the region that the game indicates it expects to run in via data in the header(or in an internal database for a few games that may have bad header data).
- overseas_ntsc - Overseas(non-Japan), NTSC
  Region used in North America.
- overseas_pal - Overseas(non-Japan), PAL
  Region used in Europe.
- domestic_ntsc - Domestic(Japan), NTSC
  Region used in Japan.
- domestic_pal - Domestic(Japan), PAL
  Probably an invalid region, but available for testing purposes anyway.

md.reported_region

enum

same
game
overseas_ntsc
overseas_pal
domestic_ntsc
domestic_pal

same

Region reported to the game.

- same - Match the region emulated.
- game - Match game's header.
  This option, in conjunction with the "md.region" setting, can be used to run all games at NTSC speeds, or all games at PAL speeds.
- overseas_ntsc - Overseas(non-Japan), NTSC
  Region used in North America.
- overseas_pal - Overseas(non-Japan), PAL
  Region used in Europe.
- domestic_ntsc - Domestic(Japan), NTSC
  Region used in Japan.
- domestic_pal - Domestic(Japan), PAL
  Probably an invalid region, but available for testing purposes anyway.

Setting: | Value Type: | Possible Values: | Default Value: | Description:
--- | --- | --- | --- | ---

md.debugger.disfontsize

enum

5x7
6x9
6x12
6x13
9x18

5x7

Disassembly font size.

Note: Setting the font size to larger than the default may cause text overlap in the debugger.

- 5x7 - 5x7
- 6x9 - 6x9
- 6x12 - 6x12
- 6x13 - 6x13. CJK support.
- 9x18 - 9x18; CJK support.

md.debugger.memcharenc | string |  | shift_jis | Character encoding for the debugger's memory editor.
md.enable | boolean | 0 1 | 1 | Enable (automatic) usage of this module.
md.forcemono | boolean | 0 1 | 0 | Force monophonic sound output.

md.scanlines

integer

-100 through 100

0

Enable scanlines with specified opacity.

Opacity is specified in %; IE a value of "100" will give entirely black scanlines.
Negative values are the same as positive values for non-interlaced video, but for interlaced video will cause the scanlines to be overlaid over the previous(if the "video.deinterlacer" setting is set to "weave", the default) field's lines.

md.shader

enum

none
autoip
autoipsharper
scale2x
sabr
ipsharper
ipxnoty
ipynotx
ipxnotysharper
ipynotxsharper
goat

none

Enable specified OpenGL shader.

Obviously, this will only work with the OpenGL "video.driver" setting, and only on cards and OpenGL implementations that support shaders, otherwise you will get a black screen, or Mednafen may display an error message when starting up. When a shader is enabled, the "md.videoip" setting is ignored.

- none - None/Disabled
- autoip - Auto Interpolation
  Will automatically interpolate on each axis if the corresponding effective scaling factor is not an integer.
- autoipsharper - Sharper Auto Interpolation
  Same as "autoip", but when interpolation is done, it is done in a manner that will reduce blurriness if possible.
- scale2x - Scale2x
- sabr - SABR v3.0
  GPU-intensive.
- ipsharper - Sharper bilinear interpolation.
- ipxnoty - Linear interpolation on X axis only.
- ipynotx - Linear interpolation on Y axis only.
- ipxnotysharper - Sharper version of "ipxnoty".
- ipynotxsharper - Sharper version of "ipynotx".
- goat - Simple approximation of a color TV CRT look.
  Intended for fullscreen modes with a vertical resolution of around 1000 to 1500 pixels. Doesn't simulate halation and electron beam energy distribution nuances.

md.shader.goat.fprog

boolean

0
1

0

Force interlaced video to be treated as progressive.

When disabled, the default, the "video.deinterlacer" setting is effectively ignored with respect to what appears on the screen, unless it's set to "blend" or "blend_rg". When enabled, it may be prudent to disable the scanlines effect controlled by the "md.shader.goat.slen" setting, or else the scanline effect may look objectionable.

md.shader.goat.hdiv | real | -2.00 through 2.00 | 0.50 | Constant RGB horizontal divergence.

md.shader.goat.pat

enum

goatron
borg
slenderman

goatron

Mask pattern.

- goatron - Goatron
  Brightest.
- borg - Borg
  Darkest.
- slenderman - Slenderman
  Spookiest?

md.shader.goat.slen | boolean | 0 1 | 1 | Enable scanlines effect.
md.shader.goat.tp | real | 0.00 through 1.00 | 0.50 | Transparency of otherwise-opaque mask areas.
md.shader.goat.vdiv | real | -2.00 through 2.00 | 0.50 | Constant RGB vertical divergence.

md.special

enum

none
hq2x
hq3x
hq4x
scale2x
scale3x
scale4x
2xsai
super2xsai
supereagle
nn2x
nn3x
nn4x
nny2x
nny3x
nny4x

none

Enable specified special video scaler.

The destination rectangle is NOT altered by this setting, so if you have xscale and yscale set to "2", and try to use a 3x scaling filter like hq3x, the image is not going to look that great. The nearest-neighbor scalers are intended for use with bilinear interpolation enabled, for a sharper image, though the "autoipsharper" shader may provide better results.

- none - None/Disabled
- hq2x - hq2x
- hq3x - hq3x
- hq4x - hq4x
- scale2x - scale2x
- scale3x - scale3x
- scale4x - scale4x
- 2xsai - 2xSaI
- super2xsai - Super 2xSaI
- supereagle - Super Eagle
- nn2x - Nearest-neighbor 2x
- nn3x - Nearest-neighbor 3x
- nn4x - Nearest-neighbor 4x
- nny2x - Nearest-neighbor 2x, y axis only
- nny3x - Nearest-neighbor 3x, y axis only
- nny4x - Nearest-neighbor 4x, y axis only

md.stretch

enum

0
full
aspect
aspect_int
aspect_mult2

aspect_mult2

Stretch to fill screen.

- 0 - Disabled
- full - Full
  Full-screen stretch, disregarding aspect ratio.
- aspect - Aspect Preserve
  Full-screen stretch as far as the aspect ratio(in this sense, the equivalent xscalefs == yscalefs) can be maintained.
- aspect_int - Aspect Preserve + Integer Scale
  Full-screen stretch, same as "aspect" except that the equivalent xscalefs and yscalefs are rounded down to the nearest integer.
- aspect_mult2 - Aspect Preserve + Integer Multiple-of-2 Scale
  Full-screen stretch, same as "aspect_int", but rounds down to the nearest multiple of 2.

md.tblur | boolean | 0 1 | 0 | Enable video temporal blur(50/50 previous/current frame by default).
md.tblur.accum | boolean | 0 1 | 0 | Accumulate color data rather than discarding it.
md.tblur.accum.amount | real | 0 through 100 | 50 | Blur amount in accumulation mode, specified in percentage of accumulation buffer to mix with the current frame.

md.videoip

enum

0
1
x
y

1

Enable (bi)linear interpolation.

- 0 - Disabled
- 1 - Bilinear
- x - Linear (X)
  Interpolation only on the X axis.
- y - Linear (Y)
  Interpolation only on the Y axis.

md.xres | integer | 0 through 65536 | 0 | Full-screen horizontal resolution. A value of "0" will cause the current desktop horizontal resolution to be used.
md.xscale | real | 0.01 through 256 | 3.000000 | Scaling factor for the X axis in windowed mode.
md.xscalefs | real | 0.01 through 256 | 1.000000 | Scaling factor for the X axis in fullscreen mode. For this setting to have any effect, the "md.stretch" setting must be set to "0".
md.yres | integer | 0 through 65536 | 0 | Full-screen vertical resolution. A value of "0" will cause the current desktop vertical resolution to be used.
md.yscale | real | 0.01 through 256 | 3.000000 | Scaling factor for the Y axis in windowed mode.
md.yscalefs | real | 0.01 through 256 | 1.000000 | Scaling factor for the Y axis in fullscreen mode. For this setting to have any effect, the "md.stretch" setting must be set to "0".