# Product Vamp Technical Guide ## Repository Shape Product Vamp follows the Modulus product layout used by the khodo repos: - `include/vamp_zero` and `src/vamp_zero`: Pi Zero C++23 application. - `include/vamp_pico` and `src/vamp_pico`: Pi Pico 2 W C++17 firmware. - `include/vamp_protocol` and `src/vamp_protocol`: shared route and page-command contracts used by both devices. - `cmake/pico.cmake` and `cmake/zero.cmake`: device-specific build definitions selected by the root `CMakeLists.txt`. - `include/vamp_style.hpp`, `include/vamp_style/font.hpp`, and `src/vamp_style.cpp`: shared color palette and Petaluma font interfaces. Bitmap font data is generated in the build directory. - `data`: authored MusicXML for performance songs and practice exercises, plus the generator regression summary. - `generator`: build-time Python preprocessing for performance arrangements and practice variants. - `package`: generic bundle inputs, scripts, config, static font assets, and device install files. ## Zero Runtime The Zero process can run headless for local/API quick checks or with Luma for the Waveshare Zero-DISP-7A display. The API is plain HTTP on the private AP: - `GET /api/status` - `GET /api/remote/display` - `POST /api/remote/heartbeat` - `POST /api/remote/next` - `POST /api/remote/previous` - `POST /api/remote/select` Legacy `/api/page/next` and `/api/page/previous` routes are still accepted for simple manual checks. The AP setup pins NetworkManager to 2.4 GHz channel 6 with WPA2/RSN and CCMP ciphers so the Pico W can join using `CYW43_AUTH_WPA2_AES_PSK`. On Raspberry Pi OS Lite, the installed display service owns `tty1`, conflicts with `getty@tty1.service`, and starts the Zero container through `product-vamp-start-zero`. The wrapper switches to the display VT when `chvt` is available and runs `vamp-zero` inside the container through `setsid --wait --ctty` with `/dev/tty1` as stdin, giving raylib's DRM backend a real virtual terminal while keeping Docker attached to the long-running display process. SSH remains the normal admin path and `tty2` is enabled as the fallback local console. At startup the Zero scans `share/product-vamp/songs/*.json` and `share/product-vamp/practice////.json`, ensures the current SQLite schema with Noto, imports both catalogs, then reloads runtime menu state from the database. Runtime navigation and rendering use that loaded Noto-backed state instead of rescanning asset folders. The UI supports a top-level mode menu, Performance song/part/score menus, and Practice type/lesson/exercise/key/score menus. Melody and chord practice both offer key selection by choosing a pre-generated score variant. The score view displays build-time engraved PNG pages. Musical interpretation, spacing, beaming, ties, accidentals, and pagination happen on the build host, not on the Pi. The view retains at most two page textures. ## Score Generation The build runs `python3 -m generator` against `data/` and writes build-only assets under the CMake binary tree. Performance source songs become acoustic, electric, and vocal arrangements. Melody and chord practice sources are emitted in all 12 keys at build time. Generated JSON keeps notation metadata while removing generator-only optional chord markers. The current catalogue produces six performance scores and 48 practice variants (54 JSON bundles). The pipeline is MuseScore -> uncompressed `.xml` -> musical model -> automatic arranger/transposer -> semantic JSON plus engraved pages. Export MusicXML 3.1 or 4.0, `score-partwise`, with one part and one staff. Independent rhythmic voices remain separate; simultaneous chord tones retain their own spelling, written duration, and tie links. The packaged music describes each transformed part or practice variant, not an archival copy of the source XML. ### MusicXML Contract | Area | Accepted notation | | --- | --- | | Pitch | Exact rational letter/alteration/octave spelling, including microtones, double/triple accidentals, and courtesy accidentals. B-sharp and C-flat retain the correct octave. | | Rhythm | All fourteen MusicXML types, maxima through 1024th; up to sixteen augmentation dots; exact positive rational metric durations and separately stored written values. Time modifications must reconcile the two. | | Chords and rests | Independent voice lanes, simultaneous chord tones, shorter additional chord tones, rests, full-measure rests, hidden events, forward spacers, and rhythm slashes. | | Ties and tuplets | Per-pitch ties, including partial chord ties; nested and cross-bar tuplet spans. Nested tuplets require explicit `tuplet-actual` and `tuplet-normal` numbers. | | Small notes | Grace notes with zero metric duration, cue notes, and measured single/paired tremolos. | | Staff state | G/F/C, percussion, TAB, and no-clef staves; tablature string/fret/tunings; octave clefs and octave-shift spans; standard major/minor/modal keys or custom seven-letter alterations; key, clef, and meter changes. | | Meter | Simple, compound, additive, mixed-denominator, and unmetered timelines. A partial measure must be marked `implicit="yes"`; an initial implicit measure is the arrangement pickup. Leading rests are retained. | | Harmony | Structured roots, kinds, inversions, slash basses, and degree additions/alterations/subtractions. Harmony events have their own offsets, including inside held notes. Their positions never split or shorten notes. | | Text | Title, composer, part name, multiple lyric verses with syllabification, elisions, and extenders, rehearsal labels at measure starts, and Vamp directives. | | Tempo | Metronome directions and positive quarter-note BPM from ``, either within a direction or directly in a measure. Playback/navigation attributes on `sound` are rejected. | Multiple staves/parts, repeats/navigation, slurs, dynamics, articulations, and expressive ornaments are outside the product contract and rejected. Unknown musical elements also fail. Serialized times and alterations use reduced signed-64-bit numerators and positive denominators; pitch octaves are -4 through 16, clef/octave shifts span at most three octaves, and meter counts are 1-1024 with denominator units 1-4096. These resource bounds produce diagnostics, not clamping or truncation. Layout/exporter information such as page defaults, credits, print layout, font/color/position attributes, and source pagination does not determine the small-screen layout. Engraving is regenerated. Beam groups and written note values are retained; unrelated engraving metadata does not authorize ignoring musical descendants. `defusedxml==0.7.1` forbids XML entities and external access. Ordinary MusicXML DOCTYPE declarations are allowed without fetching their DTDs. ### Vamp Metadata In MuseScore's score properties, set `vamp:style` to a supported player style. It exports as standard MusicXML miscellaneous metadata: ```xml Medium Swing ``` The default is Medium Swing; `Med.`, `Med. Swing`, and `Medium` remain aliases. A keyless melody or chord exercise needs `vamp:tonic` (for example, `C`) as its transposition reference. Modes and local key changes are preserved when generating practice variants. Keyless variants remain unkeyed in the music and show their selected transposition reference in menus, for example `D (no key)`. Place staff text `vamp:optional-chord` at the same onset as exactly one harmony to mark a turnaround omitted from the final arrangement section. The text may be hidden. Parenthesizing an ordinary chord does not make it optional. Orphaned/duplicate markers and unknown `vamp:` properties are errors; consumed directives never enter runtime JSON. ### Runtime Schema A bundle has three top-level fields: - `schema_version: 3`. - `music`: metadata and a single staff containing measures, independent voice lanes, timed harmonies/attributes/tempos, instruments, tuplets, and octave spans. - `presentation`: engraver/version, style checksum, fixed width/height, and ordered relative PNG paths with SHA-256 checksums. Measure durations, event onsets/durations, harmony offsets, span times, and pitch alterations use `{ "numerator": N, "denominator": D }`. Times are in quarter-note units and alterations in semitones. There is no tick grid, display-duration surrogate, or runtime flattening into one voice. Written note types, dots, and time modifications remain distinct from metric duration. Every event owns a voice; every chord tone has its own ID, written duration, duration, and reciprocal tie links. Tuplets reference events and belong to one voice. The arranger normalizes instrument transposition to concert pitch and preserves all source voices in source-copy sections. Generated guitar rhythms occupy one lane. The seven-section form, optional turnaround handling, and twelve melody/chord practice keys remain automatic. Generated guitar voicings and chord-practice validation share standard six-string tuning (E2 A2 D3 G3 B3 E4), frets 0-15 inclusive, and a maximum four-fret difference between fretted positions; open strings do not count toward that span. The arranger searches all candidates in that range and retains its existing deterministic scoring and voicing policy. Unplayable performance harmonies still produce a warned rhythmic-slash fallback without changing the structured chord meaning or quantizing microtones. Chord practice transposes from the source key, not from its first chord: the current C-key cycle begins with G7, so selecting D produces an opening A7. It preserves every authored tone, interval, inversion, rhythmic voice, tie, and tuplet. The closest transposition is tried first, followed by whole-exercise octave alternatives ordered by absolute displacement, with upward movement preferred on ties. Register adjustment does not change harmony symbols or key signatures. Sustained and tied tones keep their strings as other voices enter. This is a fretboard feasibility check, not a guarantee of comfortable fingering, and does not apply the performance arranger's chord-tone omissions or revoicing. For the fretboard check, ordinary unmarked treble notation uses the project's written-guitar convention (one octave above sounding pitch). An explicit MusicXML instrument transposition is applied instead, once, including an explicit zero interval; the importer records this distinction with `transpose.explicit`. Octave-clef and TAB pitches do not receive the implicit octave subtraction. Nonstandard tunings, capo configurations, microtonal frets, or exercises that cannot retain their voicings in every key fail explicitly. Errors identify the source, target key, and failing passage; existing generated assets are preserved. The current G cycle variant needs a whole-exercise octave increase to stay above the guitar's lowest note. Automatic performance arrangements require a pitched, non-TAB lead. Percussion and tablature remain available in the model and melody-practice pipeline, but conversion into guitar/vocal parts fails explicitly rather than reinterpreting percussion positions or fret numbers as ordinary treble-staff notation. Chord practice requires pitched guitar notation. Practice transposition retains authored TAB strings and never invents a new fingering; chord practice additionally checks that the resulting exact integer frets lie within 0-15. Melody practice retains its existing nonnegative-fret behavior. ### Engraving Boundary `generator/engraving/` is a custom Python engraver, not a wrapper around MuseScore or another notation engine. `layout_score(document, style, fonts)` produces immutable layout pages with exact source intervals, notation anchors and drawing primitives. `rasterize_page(page, fonts)` draws one page at four-times resolution and downsamples it. `engrave_tree(root, fonts)` retains the asset-pipeline entry point. `generator/musicxml_writer.py` remains a round-trip/export utility and is not involved in engraving. `notation.py` interprets staff state, exact pitch positions and shared accidental state; `notes.py` and `attributes.py` construct symbols; `spans.py` handles beams, ties, tuplets, octave shifts and lyric continuations; `layout.py` handles spacing and pagination. `fonts.py` reads bundled OTF outlines and SMuFL metadata, caching metrics and outlines for one generation run. `raster.py` uses FontTools, aggdraw and Pillow only as low-level font and drawing libraries. All dependencies are pinned in `tools/requirements.txt` and remain build-only. Standard glyph names and their upstream notice are vendored alongside the fonts; no system music fonts are consulted. The former backend-specific four-voice, duration, unequal-tone and tuplet restrictions are removed. Voices retain separate stems and collision offsets; chord tones retain their own written durations and per-tone ties. Pitched, percussion and explicitly fingered TAB material use their own staff positions. Unknown exact microtonal alterations use a numeric rational semitone annotation relative to the natural pitch, not a rounded accidental. An explicit unavailable SMuFL glyph is an error. The single-part/single-staff importer contract and exclusions for dynamics, accents, expressive ornaments and navigation remain unchanged. `audit.py` checks the final layout against the musical model: timeline and fragment coverage, exact fragment durations, actual glyph bounds, pitch positions, visible note primitives, required accidentals, ties, lyrics, harmonies, tempos and spans. It rejects out-of-page geometry and collisions among unrelated noteheads, accidentals and same-lane text. Staff, ledger, stem, beam and tie contacts are intentional. This is not a proof of publication-quality engraving for every possible MusicXML document; notation changes need targeted semantic, geometry and reviewed image tests. The writer's XML round-trip audit is retained separately in the test suite. Bundles keep schema version 3 and an unchanged `music` object. Presentation identifies `Vamp Python` version `1.0.0`; its style fingerprint includes the style settings, both font files, font-specific metadata and the glyph-name mapping. Runtime remains engine-agnostic, so valid existing schema-v3 bundles need no database migration. Pages are 976x484 pixels with 12-pixel staff spacing, 28-pixel horizontal margins and 18-pixel vertical margins. Dense measures continue across systems/pages; sustained notes become exact, tied presentation fragments and rests become exact rest fragments. These fragments never change the semantic JSON. Irreducible simultaneous content that cannot fit a fixed page fails contextually rather than being clipped or shrunk. Blank pages, incorrect dimensions, and ink reaching the page edge are rejected. Runtime letterboxing preserves aspect ratio. Luma's `load_texture_uncached()` lets Product Vamp retain at most two textures without a hidden strong asset-cache reference. The UI reports missing/corrupt assets instead of falling back to the removed renderer. Runtime validates bundle metadata, paths, dimensions, and page checksums; the build validates musical semantics. ### Validation And Migration Generation validates sources and complete staged output before replacing the previous asset directory. Replacement is always complete, including when the compatibility `--clean` flag is omitted; deleted sources cannot leave stale JSON or pages. CMake tracks the input list as well as file contents, so additions and removals regenerate the catalogue. Runtime packages contain semantic JSON, PNG pages, and the OTF UI text font, not MusicXML, MuseScore, or Python dependencies. Python test discovery runs model/import/export tests; the normal asset build additionally qualifies and audits every catalogue score. Diagnostics identify the file, part, measure, and unsupported element or invalid relationship. Examples include `part P1, measure 4: unsupported musical element `, `tie stop has no contiguous matching start`, and `optional-chord marker must identify exactly one harmony`. The six compact source files were replaced, not retained as a second authoring format. Existing catalogue rows refresh from regenerated JSON at startup. Custom database rows (`catalog_managed = 0`) are retained, including ID conflicts, and are never automatically deleted to resolve a schema mismatch. Custom legacy JSON must be regenerated as a schema-v3 bundle with page assets; the loader reports a regeneration error instead of interpreting old ticks heuristically. References: [MusicXML durations](https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/duration/), [tuplets](https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/tuplet/), [degree alterations](https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/degree-alter/), and [SMuFL accidentals](https://smufl.formats.music/latest/tables/standard-accidentals-12-edo.html). Generator checks compare the generated performance summary against `data/expected/performance_summary.json`. The summary stores compatibility invariants such as section layout, chord-label placement, slash-section placement, and vocal timing without committing the generated score files themselves. Refresh that file only when an intentional arrangement-logic change should become the new baseline. ## Pico Runtime The Pico firmware uses the Pico SDK C++ stack and the `pico2_w` board definition. It initializes the ST7789T3 display over SPI, reads the CST816D touch controller over I2C, joins the Zero AP, polls `/api/remote/display`, and sends HTTP POST commands for gestures. The display is rotated 90 degrees clockwise into a 320x240 landscape UI. The top status bar uses the shared palette: - Blue: connecting. - Yellow: retrying or remote request failed. - Green: connected to the Zero API. The body stays blank until a performance or practice score is active, then it shows the active title, selected part or active practice key, and page count. Touch controls are tap for next, double tap for previous, and tap-and-hold for select. The Pico text renderer uses an antialiased bitmap atlas generated from `package/assets/fonts/petaluma/PetalumaScript.otf`. The shared font CMake rule generates `generated/vamp_style/font.cpp` separately in each native/Pico build directory, using `tools/generate_pico_font.py --output `. Font and generator changes trigger regeneration. The generated atlas includes ASCII kerning pairs so display text such as `VAMP` uses the same spacing as the source font. The pinned Pillow build dependency is declared in `tools/requirements.txt`. The root `CMakeLists.txt` is also the Pico firmware entrypoint when configured with `-DVAMP_PICO_FIRMWARE_PROJECT=ON`. That mode returns before the Zero/Linux targets are declared, so the Pico build can use the embedded ARM toolchain cleanly. Build defaults can be overridden at package time with CMake cache variables: - `VAMP_PICO_WIFI_SSID` - `VAMP_PICO_WIFI_PASSPHRASE` - `VAMP_ZERO_HOST` - `VAMP_ZERO_PORT` ## Packaging Modulus packages the CMake install stage. Product Vamp uses `install_prefix` `.` so the registry artifact is a top-level multi-device bundle rather than a root filesystem overlay. The ARM64 package target builds: - `zero/product-vamp-zero-linux-arm64.docker.tar` - `pico/product-vamp-pico2w.uf2` - `manifest.json` Building the full package requires Docker/buildx, the ARM embedded GCC toolchain, and the Pico SDK. CI passes `PICO_SDK_PATH` directly. The generated Modulus Docker image also carries the pinned Pico SDK at `/opt/pico-sdk` for local package builds. The Zero Docker runtime targets Debian trixie to match current Raspberry Pi OS and the ARM64 dependency binaries, and includes `util-linux` for the `setsid --wait --ctty` launch path. Generated score assets are created during CMake build/package and copied into the Zero image context. Static font assets remain tracked under `package/assets/fonts`. CI builds the generic artifact with `python3 modulus.py package --version latest`, then `package/scripts/publish_latest_generic_package.py` replaces the Gitea generic package version `latest` and deletes older Product Vamp generic package versions. ## Shared Protocol The Pico firmware does not link Zero-side Linux application libraries such as Ligo, Luma, or Noto. Those remain Zero-side dependencies: Ligo serves the HTTP API, Luma renders the Zero display, and Noto owns SQLite persistence. Cross-device code should stay in `vamp_protocol` and `vamp_style`: plain C++17 with no OS, allocator-heavy, or Zero-only dependencies. Luma owns the application shell, UI control tree, texture loading, and UI-thread texture lifetime. Product Vamp's page cache uses the uncached loading API; there is no score-specific Raylib font cache or handwritten notation renderer. ## LSP `tooling.editor.clangd` in `modulus.json` generates the ignored `.clangd`, pointing native Zero and shared protocol code at `build/build_x86_debug`, and Pico code at `build/build_pico_debug`. Refresh both compile databases with: ```sh python3 modulus.py lsp ``` The `tooling.lsp` section in `modulus.json` owns the Pico CMake configure. It unsets host compiler variables before configuring the Pico SDK project so clangd sees the embedded ARM toolchain. When running directly outside the generated Modulus Docker image, set `PICO_SDK_PATH` before refreshing the Pico database.