O2Emu: An SGI O2 (IP32/Moosehead) Emulator

A from-scratch emulator for the SGI O2 workstation (codename "Moosehead", SGI IP32). Phase 1 (Research) and Phase 2 (Emulation) are complete — every hardware subsystem has a sourced register map, and the full C++ emulator (CPU, memory, graphics, I/O, PROM firmware, GUI) is implemented.

Status: Phase 1 & 2 complete, Phase 3 starting. All hardware documentation is in docs/, including the SGI ASIC specs (CRIME/MACE/GBE/VICE) under docs/manuals-specs/.

What is the SGI O2?

The O2 is a 1996 SGI workstation built around a proprietary high-bandwidth Unified Memory Architecture (UMA) — the CPU, graphics, and I/O all share a single pool of main memory over a 133 MHz 144-bit bus (128-bit data + ECC).

• CPU: MIPS R5000/RM7000 (low-end) or R10000/R12000 (high-end)
• Memory: up to 1 GB of proprietary 239-pin SDRAM DIMMs (8 slots)
• Graphics: CRM chipset (Microprocessor + ICE, MRE, Display ASICs) — no separate VRAM; textures/framebuffer live in main memory
• I/O: MACE ASIC (64-bit PCI, ISA, PS/2, 10/100 Ethernet), UltraWide SCSI
• OS: IRIX 6.3/6.5.x (native), Linux, OpenBSD, NetBSD

Project goals

1. Document the O2 hardware in exhaustive detail (registers, memory map, firmware) — see docs/.
2. Emulate the machine: CPU, memory controller (MRE), graphics (CRM), I/O (MACE), and the IP32 PROM firmware.
3. Boot IRIX and/or a hobbyist OS on the emulator.

Roadmap

This project is developed in three phases. See ROADMAP.md for the full plan.

• Phase 1 — Research ✅ complete: exhaustive, well-sourced hardware documentation under docs/. All register maps sourced.
• Phase 2 — Emulation ✅ complete: a full-fledged C++ emulator, as accurate to the hardware as the documentation and specs allow. CPU, memory, graphics, I/O, and the PROM firmware, with a GUI.
• Phase 3 — Performance & polish (current): JIT compilation, optimizations, GUI improvements, cross-platform support, and full-featured emulator features.

Documentation

Topic	File
System architecture	docs/architecture.md
CPU & memory	docs/cpu-memory.md
Graphics (CRM/ICE/MRE/Display)	docs/graphics.md
I/O (MACE, PCI, SCSI, Ethernet)	docs/io.md
Register maps (from drivers)	docs/register-maps.md
PROM firmware	docs/prom.md
Research sources	docs/sources.md
Phase 1 checklist	docs/phase1-checklist.md

Firmware

The actual IP32 PROM images are included in samples/:

• ip32prom.rev4.18.bin — MD5 c9725e036052cf1f3e6258eb9bc687fa
• ip32prom.rev4.3.bin — MD5 6b86b20727a598ed15d93f27c9a3f2e8

The PROM has also been decompiled into MIPS assembly under samples/decompiled-prom/. The auto-generated definitions.h is the authoritative source for the IP32 address map and the CRIME/MACE/UART/RTC register maps.

Research sources

• Linux kernel — arch/mips/sgi-ip32/ and arch/mips/include/asm/ip32/
• NetBSD — sys/arch/sgimips/
• Leaked IRIX source — IRIX 6.5.7m and 6.5.17 (includes the actual IP32 PROM source under stand/arcs/)
• mattst88/ip32prom-decompiler — Rust tool for decompiling the IP32 PROM

See docs/sources.md for the full list.

License

BSD 3-Clause License. See LICENSE.