Sortie de la version 0.2.0 !
http://groups.google.com/group/neods/files
lceman (./2) :
En fait l'auteur de l'émul a été assez malin. Au lieu de faire de l'émulation 2D pure des jeux Neogeo, la DS en serait surement incapable, il a utilisé les capacités 3D de la machine.
D'après ce que j'ai compris, il utilise chaque sprite comme une texture. C'est le même système que les jeux de baston 2D sur PS2 (qui sont en fait "techniquement" en 3D).
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.
