This emulator is being written just for fun and for teaching to friends how to write game emulators. It is not meant to ever grow user-friendly features for now, and can just be used as a source code reference on how emulators works. It focuses only on accuracy (not performance).

How to use

$ genemu romfile

Genemu supports both bin and smd romfiles. Use --help for some additional command line option.

What's emulated

• All the basics: CPUs, sprites, planes, DMA, etc.
• PAL vs NTSC timings
• Accurate Z80 RESET/BUSREQ process
• Correct hinterrupt / hv counter
• Correct sprite priority vs bkg
• Correct sprite overflow and masking
• Wide resolution change (32 vs 40 cells)
• Shadow / highlight mode
• FM sound (YM2612)
• Basic HINTERRUPT emulation
• Vertical cell scrolling through VSRAM
• Window horizontal clipping

Todo list

The following is a rough list of missing features or things to be fixed:

• Interlace mode
• SN7689 audio chip
• Accurate timing for DMA
• The infamous "window bug"

Branches

The branch "precise_dma_fifo" implements sub-scanline timing of hblank and tries to emulate precise DMA and FIFO timings, down to full access slot emulations, but without going down to a per-cycle emulation. It is quite tricky to get everything right, but the branch is almost to a zero regressions with a few improvements with advanced effects. A few things that work better in the branch:

• DMA effects timed with HBLANK seems to work better (eg: 512-color pictures used in demos). In fact, I think the master code can get to the same level of accuracy with a few hacks on timing (to be verified).
• Direct Color mode used in demos. This still requires a hack since we still do per-scanline VDP rendering, but the DMA is almost perfectly synchronized with the emulation; the images still appear off-center and partly off-screen, but I'm still surprised they kind of work.