# Architecture - RetroBIOS ## Directory structure ``` bios/ BIOS and firmware files, organized by Manufacturer/Console/ Manufacturer/Console/ canonical files (one per unique content) .variants/ alternate versions (different hash, same purpose) emulators/ one YAML profile per core/engine platforms/ one YAML config per platform (scraped from upstream) _shared.yml shared file groups across platforms _registry.yml platform metadata (logos, scrapers, status, install config) _data_dirs.yml data directory definitions (Dolphin Sys, PPSSPP...) targets/ hardware target configs + _overrides.yml provenance/ dump-catalog snapshots (redump, no-intro, tosec) scripts/ all tooling (Python, pyyaml only dependency) scraper/ upstream scrapers (libretro, batocera, recalbox...) scraper/targets/ hardware target scrapers (retroarch, batocera, emudeck, retropie) exporter/ native format exporters (batocera, recalbox, emudeck...) install/ JSON install manifests per platform targets/ JSON target manifests per platform (cores per architecture) data/ cached data directories (not BIOS, fetched at build) schemas/ JSON schemas for platform and emulator YAML (checked in CI) tests/ test suite with synthetic fixtures wiki/ hand-written documentation sources docs/ generated MkDocs site (gitignored, rebuilt in CI) _mame_clones.json MAME parent/clone set mappings database.json file index built from bios/ (SHA1 primary key) dist/ generated packs (gitignored) .cache/ hash cache and large file downloads (gitignored) ``` `docs/` is never edited by hand: `generate_site.py` rebuilds it from `platforms/`, `emulators/`, `database.json`, and the `wiki/` sources. Documentation changes belong in `wiki/` or in the generator. ## Data flow ``` Upstream sources Scrapers parse generate_db.py scans System.dat (libretro) + fetch versions bios/ on disk batocera-systems builds database.json es_bios.xml (recalbox) (SHA1 primary key, core-info .info files indexes: by_md5, by_name, FirmwareDatabase.cs by_crc32, by_sha256, by_path_suffix) bios_db.json.zip (MiSTer) MAME/FBNeo source provenance/*.json generate_db.py joins database.json entries carry redump, no-intro, by SHA1, then by a provenance field naming tosec snapshots MD5 + size the catalogs that list them emulators/*.yml verify.py checks generate_pack.py resolves source-verified platform-native files by hash, builds ZIP from code verification packs per platform truth.py generates diff_truth.py export_native.py ground truth from compares truth vs rewrites each platform's emulator profiles scraped platform own file, corrected ``` Pipeline runs all steps in sequence: DB, provenance report, data dirs, MAME/FBNeo hashes, verify, packs, install manifests, target manifests, consistency check, pack integrity, README, site. See [tools](tools.md) for the full pipeline reference. ```mermaid graph LR A[generate_db] --> A2[provenance report] A2 --> B[refresh_data_dirs] B --> C[MAME/FBNeo hashes] C --> D[verify --all] D --> E[generate_pack --all] E --> F[install manifests] F --> G[target manifests] G --> H[consistency check] H --> H2[pack integrity] H2 --> I[generate_readme] I --> J[generate_site] style A fill:#2d333b,stroke:#adbac7,color:#adbac7 style D fill:#2d333b,stroke:#adbac7,color:#adbac7 style E fill:#2d333b,stroke:#adbac7,color:#adbac7 style H2 fill:#2d333b,stroke:#adbac7,color:#adbac7 style J fill:#2d333b,stroke:#adbac7,color:#adbac7 ``` ## Three layers of data | Layer | Source | Role | |-------|--------|------| | Platform YAML | Scraped from upstream | What the platform declares it needs | | `_shared.yml` | Curated | Shared files across platforms, reflects actual behavior | | Emulator profiles | Source-verified | What the code actually loads. Used for cross-reference and gap detection | The pack combines platform baseline (layer 1) with core requirements (layer 3). Neither too much (no files from unused cores) nor too few (no missing files for active cores). A same-named local file that contradicts an explicit hash is recorded as an unsafe omission on hash-verifying platforms; existence platforms ship it and report the divergence, because their code never reads the bytes. The emulator's source code serves as ground truth for what files are needed, what names they use, and what validation the emulator performs. Platform YAML configs are scraped from upstream and are generally accurate, though they can occasionally have gaps or stale entries. The emulator profiles complement the platform data by documenting what the code actually loads. When the two disagree, the profile takes precedence for pack generation: files the code needs are included even if the platform does not declare them. Files the platform declares but no profile references are kept as well (flagged during cross-reference), since the upstream may cover cases not yet profiled. ```mermaid graph TD PY[Platform YAML
scraped from upstream] --> PG[Pack generation] EP[Emulator profiles
source-verified] --> PG SH[_shared.yml
curated shared files] --> PY SH --> EP PG --> ZIP[ZIP pack per platform] style PY fill:#2d333b,stroke:#adbac7,color:#adbac7 style EP fill:#2d333b,stroke:#adbac7,color:#adbac7 style SH fill:#2d333b,stroke:#adbac7,color:#adbac7 style PG fill:#2d333b,stroke:#adbac7,color:#adbac7 style ZIP fill:#2d333b,stroke:#adbac7,color:#adbac7 ``` ## Dump-catalog provenance Snapshots of the dump-preservation catalogs (Redump, No-Intro, TOSEC) live in `provenance/` as committed JSON. `generate_db.py` joins them against the collection by SHA1, falling back to MD5 + size, and writes a `provenance` field on each matching database entry. The system pages render it as a verified dump badge. Provenance is an annotation, never an authority. It answers "does this file byte-match a catalogued dump", which is a different question from "does the emulator accept it". When the two disagree, pack contents and verification follow the emulator source code. `provenance_report.py` reports the reverse direction: catalog entries absent from the collection, which become acquisition targets. A DAT counts as covered when the collection holds at least one of its entries; entries from DATs the collection does not cover are counted but not listed, since No-Intro tags every non-game dump as `[BIOS]`, including tens of thousands of digital-distribution entries that are out of scope here. ## Pack grouping Platforms that produce identical packs are grouped automatically. RetroArch and Lakka share the same files and `base_destination` (`system/`), so they produce one combined pack (`RetroArch_Lakka_BIOS_Pack.zip`). RetroPie uses `BIOS/` as base path, so it gets a separate pack. With `--target`, the fingerprint includes target cores so platforms with different hardware filters get separate packs. Emulator and system packs also retain system identity, `variant_group` and requested region; same-named regional files are never collapsed merely because their display label matches. ## Pack reproducibility A pack is a function of its inputs. Two builds from the same collection and the same `database.json` produce the same bytes, so a third party can rebuild a published pack and compare it against the checksum in `SHA256SUMS.txt`. That list is signed with a release key whose public half is `allowed_signers` at the repository root, so the comparison does not rest on the release page being intact: see [verifying a release](release-process.md#verifying-a-release). Three things make that hold. Generated members (`README.txt`, `manifest.json`) carry a fixed date rather than the wall clock, and the manifest's `generated` field is read from `database.json` instead of the build time. MAME and FBNeo romsets are rebuilt deterministically from their ROMs, so a pack does not inherit whatever metadata the source archive happened to carry. And every member is written with the same fixed date: `ZipFile.write` copies the source file's mtime, which is the checkout time for a file from the collection and the wall clock for one the build just staged in `tmp/`. `tests/test_deterministic_zip.py` builds the same fixture twice and compares the bytes, for both the platform and the emulator pack paths. Its fixture holds a romset, because without one the comparison never reaches the rebuild path and passes while the real packs still move. ## Storage tiers | Tier | Meaning | |------|---------| | `embedded` (default) | file is in the `bios/` directory, included in packs | | `external` | file has a `source_url`, downloaded at pack build time | | `user_provided` | user must provide the file (instructions included in pack) | ## Verification severity How missing or mismatched files are reported: | Mode | required + missing | optional + missing | hash mismatch | |------|-------------------|-------------------|--------------| | existence | WARNING | INFO | N/A | | md5 | CRITICAL | WARNING | UNTESTED | Files with `hle_fallback: true` are downgraded to INFO when missing (the emulator has a software fallback). ## Discrepancy detection When a file passes platform verification (MD5 match) but fails emulator-level validation (wrong CRC32, wrong size), a DISCREPANCY is reported. The pack generator searches the repo for a variant that satisfies both. If none exists, the platform version is kept and the discrepancy stays reported. A filename or destination never overrides a declared content hash during resolution; whether a mismatch is packed is then decided by the platform's own verification mode. ## Security - install metadata is fetched from the same revision as the installer that reads it, and validated before use; - destinations are normalized and contained below the selected BIOS root; - downloads are bounded by declared and global size limits, verified with SHA256/SHA1, written to unique temporary siblings and atomically replaced; - ZIP extraction rejects traversal, absolute paths, duplicates, links, special files, encryption, excessive expansion and suspicious compression ratios; - standalone-emulator copies require explicit `--standalone-copies` consent; - CI writes only what its job needs: `validate.yml` holds `pull-requests: write` for the validation comment and labels, `deploy-site.yml` holds the Pages deploy identity, and the release job holds `contents: write` but runs only when someone dispatches it. - `safe_extract_zip()` prevents zip-slip path traversal attacks - `deterministic_zip` rebuilds MAME ZIPs so same ROMs always produce the same hash - `crypto_verify.py` and `sect233r1.py` verify 3DS RSA-2048 signatures and AES-128-CBC integrity - ZIP inner ROM verification via `checkInsideZip()` replicates Batocera's behavior - `md5_composite()` replicates Recalbox's composite ZIP hash ## Edge cases | Case | Handling | |------|---------| | Batocera truncated MD5 (29 chars) | prefix match in resolution | | `zippedFile` entries | MD5 is of the ROM inside the ZIP, not the ZIP itself | | Regional variants (same filename) | `by_path_suffix` index disambiguates | | MAME BIOS ZIPs | `contents` field documents inner structure | | RPG Maker/ScummVM | excluded from dedup (NODEDUP) to preserve directory structure | | `strip_components` in data dirs | flattens cache prefix to match expected path | | case-insensitive dedup | prevents `font.rom` + `FONT.ROM` conflicts on Windows/macOS | | frozen snapshot cores | `.info` may reflect current version while code is pinned to an old one. Only the frozen source at the pinned tag is reliable (e.g. desmume2015, mame2003) | ### File resolution chain `resolve_local_file` in `common.py` tries each strategy in order, returning the first match. Used by both `verify.py` and `generate_pack.py`. ```mermaid graph TD START([resolve_local_file]) --> S0{path_suffix
exact match?} S0 -- yes --> EXACT([exact]) S0 -- no --> S1{SHA1
exact match?} S1 -- yes --> EXACT S1 -- no --> S1B{SHA256
exact match?} S1B -- yes --> EXACT S1B -- no --> S1C{CRC32 + size,
no stronger hash?} S1C -- yes --> EXACT S1C -- no --> S2{MD5 direct
or truncated?} S2 -- yes --> MD5([md5_exact]) S2 -- no --> S3{name + aliases
no MD5?} S3 -- yes --> EXACT S3 -- no --> S4{name + aliases
md5_composite /
direct MD5?} S4 -- match --> EXACT S4 -- name only --> HM([hash_mismatch]) S4 -- no --> S5{zippedFile
inner ROM MD5?} S5 -- yes --> ZE([zip_exact]) S5 -- no --> S6{MAME clone
map lookup?} S6 -- yes --> MC([mame_clone]) S6 -- no --> S7{data_dir
cache scan?} S7 -- yes --> DD([data_dir]) S7 -- no --> S8{agnostic
fallback?} S8 -- yes --> AG([agnostic_fallback]) S8 -- no --> NF([not_found]) style START fill:#2d333b,stroke:#adbac7,color:#adbac7 style EXACT fill:#2d333b,stroke:#adbac7,color:#adbac7 style MD5 fill:#2d333b,stroke:#adbac7,color:#adbac7 style HM fill:#2d333b,stroke:#adbac7,color:#adbac7 style ZE fill:#2d333b,stroke:#adbac7,color:#adbac7 style MC fill:#2d333b,stroke:#adbac7,color:#adbac7 style DD fill:#2d333b,stroke:#adbac7,color:#adbac7 style AG fill:#2d333b,stroke:#adbac7,color:#adbac7 style NF fill:#2d333b,stroke:#adbac7,color:#adbac7 ``` ## Platform inheritance Platform configs support `inherits:` to share definitions. Lakka inherits from RetroArch, RetroPie inherits from RetroArch with `base_destination: BIOS`. `overrides:` allows child platforms to modify specific systems from the parent. Core resolution (`resolve_platform_cores`) uses three strategies: - `cores: all_libretro` - include all profiles with `libretro` in their type - `cores: [list]` - include only named profiles - `cores:` absent - fallback to system ID intersection between platform and profiles ## Hardware target filtering `--target TARGET` filters packs and verification by hardware (e.g. `switch`, `rpi4`, `x86_64`). Target configs are in `platforms/targets/`. Overrides in `_overrides.yml` add aliases and adjust core lists per target. `filter_systems_by_target` excludes systems whose cores are not available on the target. Without `--target`, all systems are included. ## MAME clone map `_mame_clones.json` at repo root maps MAME clone ROM names to their canonical parent. When a clone ZIP was deduplicated, `resolve_local_file` uses this map to find the canonical file. ## Install manifests `generate_pack.py --manifest` produces JSON manifests in `install/` for each platform. These contain downloadable file lists with SHA256 and SHA1 hashes, explicit unsafe/unavailable omissions, platform detection config, and standalone copy instructions. `install/targets/` contains per-architecture core availability. The cross-platform installer (`install.py`) uses these manifests to auto-detect the user's platform, filter files by hardware target, and download with SHA256/SHA1, size, path-containment and atomic-write checks. ## Tests The suite is discovered dynamically rather than maintained as a hand-counted subset: | File | Coverage | |------|----------| | `test_e2e.py` | resolution, verification, packs, inheritance, targets, truth and exporters | | `test_profile_sync.py`, `test_upstream.py` | source anchoring, forge parsing, revisions, cache and guarded writes | | `test_install.py`, `test_audit_regressions.py` | automatic wrappers, manifest boundaries, pipeline exits, strong hashes and safe archives | | `test_region.py` | region vocabulary, ranking, per-system grouping and repository conformance | | `test_site_exports.py`, `test_site_validation.py` | versioned exports, SQLite, metadata, accessibility structure and complete local-link graph | | parser/provenance modules | MAME, FBNeo, DAT import, merge and provenance joins | | artifact modules | deterministic ZIPs, locking, large-file cache, pack integrity and portable paths | ```bash python -m unittest discover tests -v # full suite python -m unittest tests.test_e2e -v # single module ``` `test_e2e.py`, `test_install.py`, `test_provenance.py`, the parser tests, `test_profile_sync.py` and `test_upstream.py` run on synthetic fixtures with no network and no real BIOS files. `test_pack_integrity.py`, `test_torrentzip.py` and `test_no_case_collisions.py` read the working tree and skip when the data they need is absent. See the [testing guide](testing-guide.md) for the fixture pattern and how to add a test. ## CI workflows | Workflow | File | Trigger | Role | |----------|------|---------|------| | Deploy Site | `deploy-site.yml` | push to main (platforms, emulators, wiki, scripts) + manual | validate contracts, generate site, build with MkDocs, validate rendered HTML, deploy to Pages | | Validation | `validate.yml` | pull request and push to main on bios/, platforms/, emulators/, schemas/, scripts/, tests/ | schema check and full test suite on both; BIOS hash validation and auto-label on pull requests | Releases are not built in CI: the packs are generated and checked on the maintainer's machine and uploaded with `gh`, see the [release process](release-process.md). ## License See `LICENSE` at repo root. Files are provided for personal backup and archival.