6dcdea1cf1
Three untracked files in the project root had no home in either repository: - the Xbox 360 technical reference report (a research compilation) becomes docs/reference/xbox360-re-technical-reference.md, unchanged; - XBOX360_ARCHITECTURE.md becomes docs/reference/xbox360-architecture.md, trimmed to its platform facts. Its format "status" sections (PAK unknown, mesh unknown, audio TODO) and the `just sniff` workflow predate every decoder in this repo and were wrong; - generate_export_docs.py becomes tools/generate_export_docs.py, the path the committed xbox360-exports.* already name as their generator. It lived inside a Canary checkout, so it now takes --canary and --out and fails loudly on a tree that is not Canary. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
116 lines
4.4 KiB
Markdown
116 lines
4.4 KiB
Markdown
<!-- Adopted 2026-09-16 from docs/XBOX360_ARCHITECTURE.md in the project root —
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early notes from before any of Sylpheed's formats were decoded. Only the
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platform facts are kept; the per-format "status" sections and the old
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`just sniff` workflow were out of date and are dropped. Not measured by this
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project. -->
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# Xbox 360 Architecture — RE Quick Reference
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A condensed reference for reverse engineering Xbox 360 games. The longer
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[technical reference report](xbox360-re-technical-reference.md) has the
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binary-level detail. Project Sylpheed's own formats are decoded, and each has a
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page under [`docs/re/`](../re/INDEX.md).
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---
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## CPU: IBM Xenon
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| Property | Value |
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|----------|-------|
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| Architecture | PowerPC 2.02 (64-bit ISA, 32-bit addressing in games) |
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| Cores | 3 symmetric cores × 2 SMT threads = **6 logical processors** |
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| Clock | 3.2 GHz |
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| Execution | In-order, dual-issue superscalar (no speculation) |
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| L1 I/D cache | 32 KB each, per core |
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| L2 cache | 1 MB unified, shared across all 3 cores |
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| Vector registers | **VMX-128** — 128 × 128-bit VRs per thread (vs. standard AltiVec's 32) |
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| Endianness | **Big-endian** |
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**Key for RE:** All multi-byte integer and float values in game binaries are big-endian.
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The VMX-128 extension adds dot-product instructions (`vmsum3fp128`/`vmsum4fp128`)
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and D3D pack/unpack instructions absent from standard PowerPC. Their semantics are in
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the [PowerPC instruction manual](../../tools/ppc-manual/README.md).
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---
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## GPU: Xenos (ATI R400/R500 derived)
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| Property | Value |
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|----------|-------|
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| Clock | 500 MHz |
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| Shader processors | 48 unified (3 SIMD × 16, each with 5-wide VLIW ALU) |
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| Peak throughput | ~240 GFLOPS |
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| On-chip memory | **10 MB eDRAM** (framebuffer, depth, MSAA — no separate VRAM) |
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| System RAM | 512 MB GDDR3 shared with CPU |
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| Northbridge | GPU also acts as northbridge / memory controller |
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### Command Packets (PM4)
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The GPU is driven by a **PM4 command ring buffer** written by the CPU. Key packet types:
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| Type | Description |
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|------|-------------|
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| `DRAW_INDX` | Indexed draw call |
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| `SET_CONSTANT` | Write shader constant registers |
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| `SET_TEXTURE_CONTROL` | Texture fetch constant (address, format, tiling mode) |
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| `LOAD_ALU_CONSTANT` | Load vertex shader constants |
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Xenia Canary's `src/xenia/gpu/` implements a full PM4 parser — invaluable for
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understanding draw calls and state management.
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### Texture Tiling
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Xbox 360 textures are stored **tiled** in memory, not linear; the Xenos hardware
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de-tiles on fetch. Texture data read from game files must be de-tiled before it is
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displayed. Tile size depends on the texture format (DXT1 = 4×4 blocks, etc.).
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---
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## Executable Format: XEX2
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`default.xex` is the main game executable in Microsoft's **Xbox EXE (XEX2)** format.
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| Offset | Field | Notes |
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|--------|-------|-------|
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| 0x00 | Magic | `58455832` = `XEX2` |
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| 0x04 | Module flags | Security, format flags |
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| 0x08 | Header data offset | Points to optional header list |
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| 0x10 | Security info offset | RSA signature, image hash |
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The executable contains encrypted, compressed PowerPC code. The full layout is in
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[`xex2-format.md`](xex2-format.md). This project loads and disassembles it with
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`crates/sylpheed-xex` and `crates/sylpheed-xexdb`.
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---
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## Platform File Formats
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### XPR2 — Texture Container
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| Offset | Field | Value |
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|--------|-------|-------|
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| 0x00 | Magic | `58505232` = `XPR2` |
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| 0x04 | Total size | u32 BE |
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| 0x08 | Header size | u32 BE — data starts at this offset |
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| 0x0C | Object count | u32 BE |
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Each texture object contains a D3DFORMAT, width/height/depth/mip levels, and tiled
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pixel data.
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### XWB / XSB — XACT Audio Banks
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Wave banks (`.xwb`) and sound banks (`.xsb`) are part of Microsoft's **XACT audio
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system**. Audio data is encoded as **XMA** (Xbox Media Audio), a proprietary
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Microsoft codec based on WMA Pro.
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---
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## Useful External References
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- [xboxdevwiki.net](https://xboxdevwiki.net) — Community Xbox 360 hardware documentation
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- [Xenia Canary source](https://github.com/xenia-canary/xenia-canary) — GPU/kernel RE reference
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- [xdvdfs](https://github.com/antangelo/xdvdfs) — Pure Rust XISO reader (a dependency of `sylpheed-formats`)
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- [binrw](https://binrw.rs) — Derive-macro binary format parsing (a dependency of `sylpheed-formats`)
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- [Free60 Project](https://free60project.github.io/wiki/) — Original Xbox 360 open-source hardware documentation
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