adr02_midi_library_selection.md

ADR: MIDI Implementation Strategy

Date: 2025-02-01 Status: Revised

Context

PhasorSyncRS requires realtime MIDI I/O with:

• Strict latency guarantees (<2ms)
• Hardware-level control
• Testable interfaces (per ADR01)

Decision

Implement a MIDI stack using:

1. Core Layer: midir (v0.6+)
   • Actively maintained Rust bindings
   • Port discovery via OS-native APIs

Implementation Strategy

The application uses the midir crate for MIDI I/O. The ExternalClock struct in src/external_clock.rs handles the MIDI input.

Performance Optimization

Technique	Benefit	ADR Alignment
Lock-free channels	Cross-platform concurrency	ADR00 §4
Automatic buffer mgmt	Zero-copy across OS layers	ADR00 §4.1
Batch processing	Reduced syscall overhead	ADR00 §4.1

Consequences

• Pros:

  • Actively maintained Rust bindings
  • Maintains TDD capabilities (ADR01)

• Cons:

  • Slightly higher abstraction overhead

Alternatives Considered

1. midir: Cross-platform abstraction adds latency
2. JACK: Requires external audio server
3. Pure C FFI: Lacks Rust safety guarantees