SAGE — Sega Arcade Golden-era Emulator

A modern C++20 emulator project. The first target is Dead or Alive on Sega Model 2B hardware (i960 main CPU + 315-5881 GPU + SCSP sound).

Current status: Dead or Alive boots, the dual-CPU (i960 + ADSP-21062 SHARC) pipeline runs with FIFO backpressure, the System 24 2D tilemap/text layers render, and the 3D engine rasterizes textured characters and arenas at 60 FPS. The Yamaha YMF292-F (SCSP) + 68EC000 sound board is implemented. See ROADMAP.md for the milestone list.

📸 Screenshots & Showcase

▶️ Watch the 60-second showcase — the full attract-mode sequence with textured 3D characters and arenas plus synchronized Yamaha SCSP (YMF292-F) audio, captured at 496x384 / 60 FPS and upscaled 2x.

Layout

SAGE/
├── CMakeLists.txt          C++20 build, FetchContent miniz
├── include/sage/
│   ├── rom_loader.h        RomLoader interface
│   ├── types.h             Region / RomVerify / LoadReport
│   ├── bus.h               Model 2B memory interconnect
│   ├── geometry.h          Model 2 3D geometry + rasterizer
│   ├── video.h             System 24 2D tilemap / palette / scanout
│   ├── display.h           SDL2 window / present
│   ├── cpu/                i960, m68000 (68EC000), sharc
│   └── hw/                 SCSP, SCSP DSP, i8251, sound board
├── src/
│   ├── main.cpp            CLI, status tables, boot trace, frame loop
│   ├── rom_loader.cpp      ROM table + load/verify implementation
│   ├── bus.cpp             address decoding + RAM/ROM
│   ├── geometry.cpp        display-list parse + scanline texture rasterizer
│   ├── video.cpp           2D tilemaps + palette decoding
│   ├── cpu/                i960, m68000, sharc cores
│   └── hw/                 sound_board, scsp, scsp_dsp, i8251
├── scripts/fetch_assets.sh downloads references (no ROMs)
├── references/             MAME sources + Supermodel (git-ignored)
└── roms/                   doa.zip (git-ignored, user-supplied)

Fetching assets

./scripts/fetch_assets.sh      # or: cmake --build build --target fetch-assets

This pulls the MAME Model 2 driver sources and a shallow clone of Supermodel (architecture reference). It does not download game ROMs: Dead or Alive is copyrighted material, so supply your own legally obtained doa.zip (a MAME-compatible doa set) at roms/doa.zip before running.

Build and run

cmake -B build -DCMAKE_BUILD_TYPE=Debug
cmake --build build
./build/sage                          # optionally: ./build/sage <zip> <doa|doab> [instructions]

The loader prints each ROM IC with its verified CRC32, the mapped memory regions, and the program memory range. It then resets the i960, prints the boot vector (SAT/PRCB/IP read from 0x00000000), and steps the CPU for 1000 instructions with a disassembled trace of the first 20 and a checkpoint every 200.

CPU core

src/cpu/i960.cpp is a standalone port of MAME's src/devices/cpu/i960 core (BSD-3-Clause, Farfetch'd / R. Belmont) with the MAME device framework removed: the memory_access<> cache is replaced by a BusInterface, fatalerror() by a recoverable Fault exception, and state registration / save_item dropped. Instruction semantics are kept verbatim so traces match MAME's.

Bus (src/bus.cpp) decodes the subset of model2b_0229_mem() the boot path touches: program ROM at 0x00000000, main_data ROM at 0x02000000/0x06000000, work RAM, buffer/palette/texture/luma RAM, and the CPU-control register block at 0x00e00000. Unmapped accesses are counted and return 0 rather than faulting.

Notes

• ROM files are resolved inside the archive by CRC32 first, then by filename. The archive's sound ROM and two sample ROMs are stored under labels that differ from MAME's, so CRC matching is required.
• The Internet Archive doa.zip contains the Revision B program ROMs, so the loader auto-detects the revision and reports it.
• mpr-19324.19 is present as dump D972201F (documented in the m2emu 1.1a DAT), which is accepted as a known alternate of MAME's 0D6BF454.
• Region contents are byte-swapped after loading, matching MAME's region_post_process() (visible in the big-endian samples region).