Deecy

Deecy is a very experimental Dreamcast emulator written in Zig.

Videos: Soul Calibur (May 2024), Grandia II (July 2024), DCA3 (January 2025)

Installation

• Download the latest version for your platform from the Release Page.
• Decompress the zip archive.
• Copy your bios and flash dumps as dc_boot.bin and dc_flash.bin to the data folder.
• Launch the Deecy executable and click Change Directory to select the folder where you store your DC games.

Compatibility

See issue #33

Build

Install the correct zig version (see .zigversion, I try to keep up with Mach nominated version). You can use zigup to manage your installed zig versions, or get it from https://machengine.org/docs/nominated-zig/.

zigup 0.14.0-dev.2577+271452d22

Clone and build. Zig will fetch all dependencies automatically.

git clone https://github.com/Senryoku/Deecy         # Clone the repo
cd Deecy
zig build run                                       # Build and run in debug mode without any argument
zig build run --release=fast -- -g "path/game.gdi"  # Build and run in release mode and loads a disc

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

Linux

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.
• MMU: Currently disabled by default as it is still incomplete, and a performance hit.
  • Games using it only for store queue writes with the pref intruction (like Ikaruga) should work without enabling the full support.
  • Windows CE don't work at all yet, even with full emulation on (Crashes with PC=FFFFFD1F).
  • It is slow:
    • Exception handling resort back to the interpreter.
    • No effort was made to speed up normal operation either: It is still non functioning where it matters.
• AICA:
  • Debug
• Renderer:
  • Framebuffer:
    • Improve detection of writes to framebuffer (false positives?)
    • Write back for games that need it.
  • Modifier Volumes.
    • Implemented: Inclusion volumes and shadow bit over opaque and transparent geometry.
    • Missing: Exclusion volumes.
    • Missing: Translucent MV in pre-sort mode.
  • Region Array Data Configuration are mostly ignored.
    • Z Clear bit.
    • Flush Accumulate? (Secondary accumulate buffer)
    • Multipass rendering.
  • Fog LUT Mode 2.
  • User Tile Clip, only the simplest version is supported.
  • Bump mapping.
  • Secondary accumulate buffer (very low priority, not sure if many games use this feature).
  • Mipmaps for palette textures?
  • Sort-DMA?
  • Follow ISP_FEED_CFG discard mode flag? (Find a game that turns it off)

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.

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/)
• Neill Corlett's Yamaha AICA notes
• AICA ARM7 Core tester by snickerbockers: https://github.com/snickerbockers/dc-arm7wrestler/
• Reicast https://github.com/skmp/reicast-emulator

Dependencies

Dependencies are managed by the build.zig.zon file.

• Multiple libraries from https://github.com/zig-gamedev (MIT)
• 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). CHD related features (src/disc/chd.zig) are also inspired by, or even direct ports of, their equivalent from the MAME project.

Rest is MIT.