Beautiful Bleep

Bleep Bus specification, version 0.1 (experimental)

Bleep Bus lets audio plugins exchange per-sample control signals through named operating-system shared memory. This document specifies the bus exactly enough to implement it without the reference SDK. If you only want to use the bus, read the Quickstart and the API reference instead.

Status: 0.x is experimental. Every minor version MAY change the layout; implementations MUST refuse to share a segment with a different 0.x minor version. From 1.0 on, compatibility is guaranteed within a major version.

The key words MUST, MUST NOT, SHOULD, SHOULD NOT and MAY are to be interpreted as described in RFC 2119.

Model

  • A bus is one shared-memory segment, identified by a namespace.
  • An endpoint is one plugin instance. It has a stable 64-bit UID.
  • An endpoint owns outputs and inputs (together: ports), each with a name unique per endpoint and direction.
  • A connection (cable) links an input to a source (endpoint UID, output name) with an amount. Connections are stored with the input, i.e. with the receiving endpoint.
  • Audio threads exchange blocks: an output publishes one block of samples per processing cycle; an input reads, for each connection, the block the source wrote for the reader's previous block (one block of latency).

Contents

  1. Naming — segment names and namespaces
  2. Layout — every byte of the segment
  3. Memory ordering — atomics, seqlocks and the registry lock
  4. Registry — endpoints, ports, reclamation of dead processes
  5. Timing — block stamps and the block selection rules
  6. Signals — value conventions ("virtual volts")
  7. Connections and state — cables, amounts and the saved-state format
  8. Versioning and extensions