Deecy

Deecy is a very experimental Dreamcast emulator written in Zig.

Videos: Soul Calibur (May 2024), Grandia II (July 2024)

Build and Run

Install the correct zig version (see .zigversion). You can use zigup to manage your installed zig versions.

zigup 0.14.0-dev.1911+3bf89f55c

git clone --recurse-submodules https://github.com/Senryoku/Deecy     # Clone the repo and its submodules
cd Deecy
zig build run                                                        # Build and run in debug mode without any argument
zig build run -Doptimize=ReleaseFast -- -g game/game.gdi             # Build and run in release mode and loads a gdi

You will also need to provide copies of dc_boot.bin and dc_flash.bin files in the data/ directory.

Linux

Linux isn't fully supported yet. nfd-zig (native file dialog) needs these additional dependencies on Linux:

sudo apt install libgtk-3-dev

Things I know I have to do

• Debug, debug, debug.
• Better low level emulation: Most games do not work as well when not using the HLE'd syscalls.
• ch0-DMA and ch1-DMA?
• What's "Maple V blank over interrupt"? "This interrupt is generated when a Maple interface transmission/reception operation spans V-Blank_In."
• AICA:
  • Stereo debugging
  • DSP
  • More debug
• Renderer:
  • Framebuffer:
    • Somehow detect writes to framebuffer and display it.
    • Write back for games that need it.
  • Modifier Volumes.
    • Implemented: Inclusion volumes and shadow bit over opaque and transparent geometry.
    • Missing: Exclusion volumes.
    • "Region Array Data Configuration" (written by the CPU directly to VRAM) are completely ignored. I don't know if it's actually used much.
  • Fog LUT Mode 2.
  • Secondary accumulate buffer (very low priority, not sure if many games use this feature).
  • Bump mapping.
  • Mipmaps for palette textures?
  • Sort-DMA?
  • User Tile Clip, only the simplest version is supported.
  • Follow ISP_FEED_CFG discard mode flag? (Find a game that turns it off)
• MMU: Only supported for store queue writes using the pref intruction (used by Ikaruga for example)

Nice to have

• Some (rendering) performance metrics directly in the emulator?
• GDROM-DMA: Uses a superfluous memcpy (gdrom -> dma-queue -> ram). Not a huge deal on my main system, but I bet it's noticeable on lower end devices.

Things I don't know I have to do

• A lot more than the previous list

Some sources

• http://www.shared-ptr.com/sh_insns.html
• SH4 Hardware Manual / Programming Manual
• https://segaretro.org/Dreamcast_official_documentation
• Dreamcast Programming by Marcus Comstedt : https://mc.pp.se/dc/
• Boot ROM disassembly by Lars Olsson (https://lars-olsson.sizious.com/, originally https://www.ludd.ltu.se/~jlo/dc/)
• AICA ARM7 Core tester by snickerbockers: https://github.com/snickerbockers/dc-arm7wrestler/
• Reicast https://github.com/skmp/reicast-emulator

Dependencies

• Multiple libraries from https://github.com/michal-z/zig-gamedev (MIT), included in libs/ as a submodule.
• ndf-zig: https://github.com/fabioarnold/nfd-zig (MIT)
• zig-lz4: https://github.com/SnorlaxAssist/zig-lz4 (MIT), bindings for LZ4 https://github.com/lz4/lz4 (BSD 2-Clause)

Thanks

• Huge thanks to drk||Raziel and MetalliC for their respective contributions to the scene, and for answering my questions!
• Thanks to originaldave_ for the sh4 tests (https://github.com/SingleStepTests/sh4)
• And overall thanks to everyone participating in the EmuDev Discord :)

Licence

• Uses data from MAME under the BSD-3-Clause licence (see src/gdrom_secu.zig).