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# Sega Genesis/MegaDrive Documentation

Last updated January 13, 2013
Valid as of 0.9.28-WIP

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. 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, heavily-modified 68K emulation core from Yabause, and Z80 emulation core from FUSE.

Sega Genesis/Megadrive emulation should still be considered experimental; there are still likely subtle 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.port1

enum

none
gamepad2
gamepad
gamepad6
megamouse

gamepad

Input device for 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 Port 2

- 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

xsmall
small
medium
large

small

Disassembly font size.

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

- xsmall - 4x5
- small - 5x7
- medium - 6x13
- large - 9x18

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.pixshader

enum

none
autoip
autoipsharper
scale2x
sabr
ipsharper
ipxnoty
ipynotx
ipxnotysharper
ipynotxsharper

none

Enable specified OpenGL pixel shader.

Obviously, this will only work with the OpenGL "video.driver" setting, and only on cards and OpenGL implementations that support pixel shaders, otherwise you will get a black screen, or Mednafen may display an error message when starting up. Bilinear interpolation is disabled with pixel shaders, and any interpolation, if present, will be noted in the description of each pixel shader.
Note: Mednafen's pixel shaders do not work properly on some AMD graphics cards(there is a diagonal line of distortion) for an unknown reason, possibly a hardware bug.

- 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".

md.scanlines | integer | 0 through 100 | 0 | Enable scanlines with specified opacity. Opacity is specified in %; IE a value of "100" will give entirely black scanlines.

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, at high resolutions(such as 1280x1024; nn2x(or nny2x) + bilinear interpolation + fullscreen stretching at this resolution looks quite nice).

- 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 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 settings to have any effect, the "<system>.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 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 settings to have any effect, the "<system>.stretch" setting must be set to "0".