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Auvra

00 — Project Overview

Purpose

Section titled “Purpose”

Auvra is an instrument-shaped plugin host designed as a dedicated hardware synthesizer. Sound comes from synth plugins (CLAP-native, open-source and commercial) combined into patches — layers/splits feeding an integrated mixer with effect-plugin support — on an N100-class real-time Linux host. The selected hardware integration target is a Tang Mega 138K Pro FPGA card for PCIe/ALSA audio, I²S converters, host-rendered GUI scanout/touch, and physical-control I/O; AES67 remains a later network-audio stage (17). The current prototype uses the keybed and chassis of a Yamaha S90 as a development base, not as the product definition. Board capability is documented, but the combined drivers, pinout, timing, latency and product rights are not yet validated. The host/patch/mixer concept is defined in 12-plugin-host-and-patches.md.

Scope of this blueprint

Section titled “Scope of this blueprint”

In scope: the system architecture and the subsystem-level design — compute platform, operating system, FPGA PCIe audio/display/control integration, keybed interfacing, analog I/O, power, and the engine architecture (plugin host, patch model, mixer — 12). The USB-audio/HDMI/USB-MIDI/MCP2221A path remains the software MVP and bench fallback; the FPGA card is the selected integrated-hardware target, subject to the gates in 17. Each subsystem document states the chosen approach, alternatives, and open questions.

Out of scope here: DSP internals of third-party plugins, the store service, and detailed schematics/PCB layout. UI behavior and implementation are defined in 13–16.

Design principles

Section titled “Design principles”
  1. Latency is the headline metric. Every architectural choice is judged first by its effect on key-to-sound latency and jitter. Target: round-trip audio < 6 ms, realistically ≈ 2.7 ms.1
  2. It is an appliance. No desktop, no login, no boot text on the panel. The OS image is immutable; user data lives on a separate writable partition. Power-loss must never corrupt the system.2
  3. Separate bench and product paths. Standard USB audio and HDMI/USB touch keep software testable; the integrated instrument targets FPGA PCIe audio, framebuffer scanout, and physical I/O.
  4. Separate the time-critical from the rest. The bench keybed scanner uses USB-MIDI; the integrated scanner sends timestamped note events through the FPGA/PCIe event path. I²C is for actual I²C peripherals and noncritical control, never the raw S90 key matrix or an unbounded note-polling path.3
  5. Document the unknowns. The S90’s internal wiring is not publicly documented; anything that must be measured on real hardware is tagged [verify].

Platform roadmap

Section titled “Platform roadmap”
Phase Compute Notes
Prototype Intel N100 (ASRock N100DC-ITX) x86, fanless, cheap, abundant Linux support.
Later ARM ITX/SBC Once the synth engine and OS image are portable. Candidates evaluated in 02-compute-platform.md.

Reading order

Section titled “Reading order”

Start with 01-system-architecture.md for the whole picture and the latency budget, then read the subsystem docs in any order. The 10-roadmap-and-risks.md register lists what is still unproven.

Glossary

Section titled “Glossary”
Term Meaning
BH keybed Yamaha “Balanced Hammer” weighted 88-key action used in the S90.
Matrix scan Reading a grid of key contacts by driving columns and sensing rows in sequence.
Velocity (make/break) Key strike speed, derived from the time between a key’s two contacts closing.4
PREEMPT_RT The Linux real-time preemption feature, mainline since kernel 6.12.5
JACK / ALSA / PipeWire Linux audio stacks; see 03-realtime-os.md.
Class-compliant A USB device usable without a vendor driver (USB Audio/MIDI/HID class).
RP2350 Raspberry Pi’s dual-core MCU (Pico 2); bench scanner/control node or optional integrated I/O helper.
Tang Mega 138K Pro Selected FPGA development card for integrated PCIe audio, display scanout, and physical I/O; hardware implementation is gated.
Kiosk A single full-screen app that owns the display with no surrounding desktop.
RTL Round-trip latency: input → processing → output, measured in ms.
CLAP CLever Audio Plug-in — the MIT-licensed plugin API Auvra hosts natively.6
Patch / Slot A saved playable setup / one of its synth-plugin positions (see 12).
AES67 Interoperable professional audio over RTP/IP with PTP-based clock synchronisation; see 17.

Naming

Section titled “Naming”

Auvra is the product and platform name, used consistently for the repository, folders, and code namespace.

Footnotes

Section titled “Footnotes”

  1. Achievable RTL on N100-class hardware with a tuned RT kernel; see 03-realtime-os.md. LinuxCNC forum, “Intel N100” latency thread. https://forum.linuxcnc.org/18-computer/50817-intel-n100 ↩

  2. ArchWiki, “Silent boot.” https://wiki.archlinux.org/title/Silent_boot ↩

  3. MIDI Association, “Jitter and latency.” https://midi.org/community/midi-connections/jitter-and-latency-usb-firewire-thunderbolt ↩

  4. Syntaur, “Check the contact strips.” https://blog.syntaur.com/?p=38 ↩

  5. Phoronix, “Real-Time PREEMPT_RT Support Merged For Linux 6.12.” https://www.phoronix.com/news/Linux-6.12-Does-Real-Time ↩

  6. CLAP — CLever Audio Plug-in API. https://cleveraudio.org/ ↩