[Hard core Rikki]

A NeoGeo emulator for the DS handheld has been released just recently. Reports say that many games run near-fullspeed, so the DS owners among you might want to try this one out. Feel free to share pics and screenshots here if you make any.
A DLDI compatible flash card is required, btw (that's more for playing homebrew stuff than an actual requirement to play it)

Quickie copypaste from the readme

NeoDS v0.1.0 by Ben Ingram
Website: NeoDS | Google Groups

If you have questions, READ THIS DOCUMENT FIRST!!! Then check the website, and the forums at gameboy advance development and www.PocketHeaven.com. If you still have questions, email me at ingramb AT gmail DOT com. I will be happy to help, but possibly slightly annoyed if your question is answered in this document.

INTRODUCTION

This is a NeoGeo AES/MVS emulator for the Nintendo DS. It can run all types of NeoGeo roms with some limitations.

Currently emulated:
* M68000 cpu (cyclone)
* Z80 cpu (DrZ80)
* All forms of NeoGeo protection/encryption
* Graphics
* ADPCM audio
* PSG audio

Not emulated:
* FM audio
* Raster effects
* Multiplayer
* Some timings are not that accurate

FM audio has already been done in jEnesisDS, so it is possible in theory. It will be hard to squeeze it into NeoDS, as both the ARM7 and ARM9 are pretty busy. But I will try. Most of the graphics in NeoDS are drawn with textured quads. Emulating raster effects using this method would require more polygons per frame than the DS is capable of (as far as I can tell). It may be possible to emulate raster effects using the DS 2D hardware, but there are lots of reasons why this would be difficult.

USING THE EMULATOR
Required:
* Nintendo DS (lite)
* DLDI compatible flash card

First, you need to patch NeoDS.nds for your DLDI flash card (NOTE - not all flashcards require patching). See here: DLDI - Dynamically Linked Device Interface for libfat. Please don't email me for help about this, there are plenty of places online that explain how this works.

Next you will need to convert some NeoGeo roms (mslug.zip for example). You also need a bios rom (neogeo.zip). NeoDS uses the same rom sets as MAME, so make sure your games work in MAME before proceeding. Put all the roms you want to convert along with the bios together in a folder. Copy NeoDSConvert.exe into the same folder. Run NeoDSConvert, and it will convert all the NeoGeo roms in that folder. The converted roms will have the *.neo extension.

Copy the DLDI patched NeoDS.nds, and all the *.neo roms into the root of your flashcard. Run NeoDS.nds. The main menu should load, showing you a list of all the roms on your card. Use the arrow keys to select, and press start to choose. The rom should load, and you should be playing. You can load a rom without audio which will improve frame rate, but you won't get any sound (obviously). Once a game is loaded without audio, the only way to get audio back is to reload the game. Some games will freeze with audio disabled, so be warned!

Controls
[Arrow keys] - Arrow keys
[A, B, X, Y] - NeoGeo face buttons
[Start] - Start
[Select] - Coin

The NeoDS gui is controlled with the stylus.
* Video - Video can be normal or scaled. Normal is a cropped screen. Scaled shows the full screen, but scaled down to fit.

* CPU Clock- The NeoGeo cpu can be underclocked. This can actually make some games run faster! It is easier for NeoDS to emulate a slower cpu, and some NeoGeo games don't use the full cpu power anyway. Experiment and see.

* Screen Off - The lower screen can be turned off. Touch anywhere to turn it back on.

* Load rom - Load a new game

Please report any crashes to me. The more info you can give me, the better. Thanks!

ADVANCED

You can run NeoDSConvert from the command line. In this case, it takes up to 2 parameters.
-bios0 use the euro bios
-bios1 use the euro-s1 bios
-bios2 use the us bios
-bios3 use the us-e bios
-bios4 use the asia bios
-bios5 use the japan bios
-bios6 use the japan-s2 bios
-bios7 use the japan-s1 bios
-bios8 use the uni-bios.10 bios
-bios9 use the uni-bios.11 bios
-bios10 use the debug bios
-bios11 use the asia-aes bios
If there is another parameter, it will be interpreted as the name of the game, as given to MAME. In this case, only this rom will be converted.

For example, pretend you want to convert Metal Slug 1, using the japan-s2 bios. Create a new directory (C:\roms). Copy mslug.zip and NeoDsConvert.exe into C:\roms. To open a command line, click start, select "run...", type "cmd", and press enter. Type "cd c:\roms". Press enter. Then type "NeoDSConvert -bios6 mslug". Press enter.

TODO
* Save states
* Faster M68k cpu core
* Improved stability
* FM audio (?)
* Raster effects (?)
* Wifi multiplayer (?)
* Clean up NeoDSConvert source if I feel like it

TECHNICAL NOTES

NeoGeo games can be close to 100MB in size, while the ds only has 4MB of ram. Graphics, sound, and program code all need to be streamed into ram constantly while the emulator is running. NeoDs uses a modified libfat which has a lookup table to vastly speed up seek times. In the future, slot2 ds ram expansion packs could provide some speed up. But they only have 32MB, so games will still have to stream.

The emulator uses a slightly modified version of Cyclone for the m68k core. The memory handlers are all done in assembly code and integrated into the core. The jump table is also compressed using a series of sub jump tables. This uses an extra arm instruction to decode each opcode, but reduces the .nds file size by ~200k, and improves cache utilization. This seems to give a slight speed increase. My feeling is that cpu emulation is heavily memory bound. I think a smaller m68k core that fit mostly into the TCM could be much faster than cyclone, even if it needed more instructions to execute each opcode.

The NeoGeo sprite graphics are all done with textured quads using the ds 3d hardware. The NeoGeo tile layer is done with a ds tile background. Doing raster effects with quads is possible in theory, but changing quads per-scanline would need way more quads per frame than the ds is capable of rendering. 2d sprites could be used instead of quads, but this has several problems. The NeoGeo can render many more sprites than the ds, so it would take a complex hblank handler to swap them on a per-scanline basis. Also, the ds can only address 1024 sprites at once. This corresponds to 256k worth of vram, which is half what I can get using quads.

The NeoGeo adpcm audio is streamed from the card and decoded in software because the NeoGeo's audio format doesn't quite match the ds hardware format. The NeoGeo PSG is mapped directly to the ds PSG hardware. FM audio would probably have to be done on the arm7. But the arm7 has very little memory, and can't afford any slowdown (or else the audio will be choppy). A faster and smaller Z80 core might be needed first.

LICENCE
The gui code is all public domain (all files that begin with gui). The NeoDSConvert code is all public domain, except where the MAME/zlib licenses apply. The emulator code is free to use for non-commercial purposes. Contact me if these terms don't work for you.

And this is why everybody prefers short quote extracts ;p