Architecture Overview

Stratux turns a Raspberry Pi + RTL-SDR dongles into a multi-band aviation receiver (1090 ADS-B, 978 UAT, OGN/FLARM on 868 MHz, AIS) and broadcasts fused traffic, weather, GPS, and AHRS data to Electronic Flight Bags as GDL90 (and several other formats) over Wi-Fi. It is a single long-running Go daemon plus a few bundled C programs, served alongside a web configuration UI.

This is the human-readable companion to the agent-oriented AGENTS.md at the repo root. For build mechanics see building.md; for the data interfaces see the integration guide and http-api.md.

The daemon (main/ → stratuxrun)

main/gen_gdl90.go holds func main() and the central shared state. Every other file in main/ is a feature module that main() wires together by launching goroutines. Three mutex-guarded globals are the spine:

• globalSettings — user config, serialized to stratux.conf. Adding a field exposes it automatically via /getSettings / /setSettings and to the web UI. See settings-reference.md.
• globalStatus — runtime status (message counts, device state, CPU temp, errors), exposed via /getStatus.
• mySituation — current GPS/AHRS fix and attitude, exposed via /getSituation.

Signal sources — three C-integration patterns

The key to the codebase is that the three signal-source families integrate with C in three different ways:

1. 978 UAT → linked C library. dump978/ is compiled into libdump978.so and bound into Go via cgo (godump978). UAT frames are decoded in-process, then parsed by uatparse (FIS-B weather, NEXRAD, …).
2. 1090ES, OGN, AIS → external subprocesses. main/sdr.go spawns dump1090 (1090ES), ogn-rx-eu (868 MHz), and rtl_ais (AIS) with exec.Command, monitors them, and auto-restarts on crash.
3. GPS / baro / IMU → direct hardware. main/gps.go (serial GPS with chip autodetect), main/sensors.go, and the sensors/ package (baro/IMU drivers).

SDR dongles are assigned to bands by EEPROM serial prefix (stratux:1090, stratux:978, …); main/sdr.go owns assignment and reconfiguration. See hardware/sdr-and-bands.md and the rest of the hardware docs.

Fusion and output

main/traffic.go is the heart: it merges traffic targets from all sources, dedupes, extrapolates positions between updates, and estimates Mode-S target distance. Outputs:

• GDL90 binary messages built in gen_gdl90.go, sent over UDP :4000 and mirrored on the /gdl90 WebSocket.
• FLARM/NMEA (flarm-nmea.go) over UDP/TCP :2000, serial, and BLE.
• X-Plane / ForeFlight-sim (xplane.go) over UDP :49002; Cursor-on-Target input (cot-in.go).
• Traffic/situation history to SQLite via main/datalog.go.

See the integration guide for the full transport map and the Capability routing bitmask.

Web UI + HTTP/WebSocket API

managementInterface() in main/managementinterface.go is the HTTP server. It serves the web UI and the JSON/WebSocket API (http-api.md). No auth — it is a local AP network. The frontend (web/) is an AngularJS single-page app (mobile-angular-ui + OpenLayers maps); each screen is a "plate" (HTML in web/plates/*.html, controller in web/plates/js/*.js).

Other binaries

• fancontrol_main/ → fancontrol (PID-controlled cooling fan, its own systemd service).
• common/ — code shared between main and fancontrol (CPU temp, aviation equations, helpers).

Repo layout

Path	What
main/	the daemon (Go)
common/	shared Go helpers
dump978/, godump978/, uatparse/	UAT: C lib, cgo wrapper, FIS-B parser
dump1090/, rtl-ais/, ogn/ogn-tracker/, image_build/pi-gen/	git submodules
sensors/	baro/IMU drivers
web/	AngularJS UI and assets
debian/	systemd units, udev rules, .deb packaging, boot/network templates
image_build/	pi-gen stages producing the Pi SD-card image
test/	standalone diagnostic tools; test-data/ sample logs; notes/ design notes
docs/	developer docs (this folder)