4. System Context (APP 011)

4.1 Context Diagram

System Context

4.2 Actors

Actor Role
HAM Operator Uses browser UI to listen, tune, adjust settings, key PTT, monitor meters
System Maintainer Starts/stops service, manages serial ports, checks logs
Yaesu FT-710 External radio device controlled via serial CAT; provides scope data via FT4222 SPI; provides audio via USB sound card
Browser Runtime Provides WebSocket, Web Audio, microphone, touch input, Canvas API

4.3 External Interfaces

Interface Protocol Endpoint Direction Description
Static UI HTTP /{path} Browser → Server Serves index.html, CSS, JS, manifest, WASM
Control WS WS /WSradio Browser ↔︎ Server JSON commands and state updates
RX Audio WS WS /WSaudioRX Server → Browser Tagged dual-codec frames (Opus/PCM, 48kHz mono)
TX Audio WS WS /WSaudioTX Browser → Server Tagged mic frames (Opus/PCM) for radio TX
Spectrum WS WS /WSspectrum Server → Browser Binary spectrum frames (v1=851B, v2=1701B)
Memory API HTTP /api/mem_channels Browser ↔︎ Server Get/set memory channels
Status API HTTP /api/status Browser → Server Full radio state JSON
Auth API HTTP /api/auth/login, /api/auth/logout, /api/auth/check Browser ↔︎ Server Session management
CAT Serial Serial USB Enhanced COM Port Server → Radio Yaesu CAT commands (38400, 8N1)
FT4222 SPI SPI Internal FTDI chip Radio → Server 850-point FFT scope data via scope_pipe.py subprocess
USB Audio IN Audio USB Audio Device Radio → Server RX audio capture via PyAudio
USB Audio OUT Audio USB Audio Device Server → Radio TX audio playback via PyAudio

4.4 Data Flows

Flow Description
CAT control flow UI action → /WSradio JSON → CatController serial command → radio response → RadioState update → broadcast
RX audio flow FT-710 USB Audio → PyAudio capture (44.1kHz Int16) → resample to 48kHz → Opus encode → /WSaudioRX tagged frames → browser AudioWorklet playback
TX audio flow Browser mic → getUserMedia (48kHz) → AudioWorklet → Opus encode (Worker) → /WSaudioTX tagged frames → Opus decode → resample 48→44.1k → PyAudio → FT-710 USB Audio
Spectrum flow (FT4222) FT-710 → FT4222 SPI → scope_pipe.py subprocess → stdout pipe → _read_scope_pipe() → parse → /WSspectrum binary → browser waterfall
Spectrum flow (fallback) CAT SM0; poll → radio_state.s_meter → ScopeHandler.update_from_radio_state() → synthetic Gaussian spectrum → /WSspectrum
State broadcast flow Poll scheduler or user command → RadioState.update() → dirty-field tracking → _broadcast_state() → /WSradio stateUpdate
PTT safety flow UI touch → sendCommand('ptt', true) → CAT TX1; → radio TX; release → TX0; (fire-and-forget) → watchdog
Polling flow PollScheduler 7-task timer → CAT queries → response parse → RadioState.update() → broadcast if changed

4.5 System Boundaries

Boundary Inside Outside
Browser boundary UI state, audio playback, mic capture, PTT safety UX Browser permission model and autoplay policy
Server boundary WebSockets, static serving, CAT serial, FT4222 scope subprocess, PyAudio I/O, Opus codec, auth Radio firmware, USB driver stack, OS audio subsystem
scope_pipe boundary FT4222 SPI read loop, frame sync, diagnostics FTDI D2XX driver, kernel VCP driver detach
Audio boundary PyAudio stream management, Opus encode/decode, WS fan-out USB audio device enumeration, sample rate negotiation

4.6 Contextual Constraints