Ashin Walpola
a5ad3dcc5d
SPATEM over the air - gn_unwrap.c accepts BTP-B port 2004 alongside 2001/2002. The serial protocol already carries the port in its V2X_RX prefix, so nothing else changed there. Note the crossover that makes this easy to get wrong: SPATEM is port 2004 but messageID 4, while MAPEM is port 2003 and messageID 5. - SpatemUperCodec decodes SPAT down to per-signal-group phase and timing. The bit layout was validated by replaying 79,042 real SPATEMs - the whole 2026-03-18 drive across 7+ RSUs plus the bench trigger - against asn1tools using the ETSI modules. All 79,042 matched on every field, none hit an unsupported branch. Two traps are pinned by tests: TimeChangeDetails is the one SEQUENCE here that is NOT extensible (5 optional bits, no extension bit), and maneuverAssistList cannot be skipped when present - it is variable-length, so it has to be walked to find where the next movement starts. - The V2X list shows one row per intersection with each signal group coloured by phase and a countdown where the RSU supplies timing. TimeMark wraps hourly, so the countdown corrects for it; without that it reads hugely negative once an hour, precisely when someone is watching it. - Entries expire after 15 s, much shorter than DENM's window: a traffic light that stopped updating is not "still green". Size caveat, deliberately deferred: SERIAL_LINK_MAX_PAYLOAD is still 512, so a SPATEM over ~498 bytes is counted as an oversize drop. The bench RSU sends 58 bytes and is unaffected, but real road RSUs measured 555 median / 1243 max, so roughly 70% would not arrive. Raising the cap also requires enlarging RX_FRAME_MAX_LEN and moving rx_item_t off the WiFi driver's callback stack, where it would otherwise overflow. RSU CAM decode - HighFrequencyContainer is a CHOICE, and a roadside unit picks rsuContainerHighFrequency, which carries no kinematics at all. The decoder bailed on that branch, so every RSU CAM was dropped - including the bench RSU, which sends CAM and SPATEM from the same station id. It now decodes for position and stationType. - RSU CAMs are kept out of UseCaseDetectionEngine. They arrive as a permanently stationary station at a fixed point, which is exactly the shape the stopped-vehicle and intersection-movement use cases match, and would raise a standing false alert for as long as the RSU was in range. CAM transmit: yawRateConfidence - YawRateConfidence has nine enumerands (0..8), so UPER needs 4 bits and "unavailable" is 8. The encoder wrote 3 bits with value 7 - one bit short and the wrong symbol - shifting every field after yawRate for any standards-strict receiver. The decoder read 3 bits too, so phone and ESP32 agreed with each other and with nothing else. - This is the third instance of that exact failure mode in this project, after CurvatureCalculationMode and the GeoNetworking reserved bytes. A round-trip test through our own decoder structurally cannot catch it, so CamEncodeGolden Test asserts the bytes asn1tools produces instead: it decoded this encoder's output and re-encoded it byte-identically. Confirmed on air afterwards - 26 of our own CAMs captured back off the OBU's receiver, all 26 accepted, where the same decoder rejected them before. DENM - Hazards now expire 60 s after their last repetition. This needs a clock, not just a filter: both source flows only emit when a DENM arrives, so a sender that drives away or loses power would never trigger a recompute and its hazard would stay on screen indefinitely. - The MQTT path was dropping every DENM for two independent reasons, both found by checking the payload against CI-CiT-MQTT_API_Documentation-v6 listing 2.6 rather than guessing: the station id key is originatingStationId, and eventPosition IS a GeoJSON Point rather than an object containing one. Also parses termination (presence is the signal), sequenceNumber, stationType and the RFC3339 detectionTime. Note roadSideUnit is 15, not 12 - the enumeration has a gap after tram(11). V2X screen - The decoded CAM/DENM list now renders on the CiT One path too; it was gated to the ESP32-C5 path and CiT One fell through to the raw MQTT topic list. Those topics move to their own tab, hidden on the ESP32-C5 path where there is no broker. Testing - Adds org.json as a test-only dependency: the android.jar stub throws "not mocked" on every JSONObject call, which made the MQTT payload parsers untestable off-device. - 23 V2X tests pass. EventDetectorTest's 4 failures are pre-existing and untouched by this change.
MicrOBU Android App
Android companion app for the micrOBU; a compact V2X on-board unit developed by HAW Hamburg and consider it GmbH for vulnerable road users (cyclists, e-bike riders, pedestrians).
The app serves as the HMI for the micrOBU hardware, handling V2X message display, sensor data collection, trip recording, and OBU communication over USB-C, Wi-Fi (dev), and Bluetooth (upcoming).
Platform: Android (Kotlin) · Min SDK: 29 (Android 10) · Target SDK: 36
What it does
Real-time V2X monitoring; subscribes to the OBU's MQTT broker and displays live CAM, DENM, SPAT, MAP, and CPM messages grouped by topic with pretty-printed JSON and TX/RX badges.
DENM transmission; triggers DENM use cases (e.g. stationary vehicle warning hln-sv) on the OBU via the consider it Use Case API (v2x-uca/input/denmtrg) with a single tap.
Sensor monitoring; live readout of phone GNSS, accelerometer, gyroscope, magnetometer, and barometer alongside OBU GNSS for cross-reference.
Trip recording; foreground service records all sensor streams and detects cycling events (braking, turning, stopping) using orientation-independent signal processing. Works fully offline with no OBU connected.
Trip review; past trips displayed on an OpenStreetMap layer with detected events overlaid as coloured pins. Tap any pin for event details.
CSV export; every sensor sample written to a timestamped CSV in real time during a session. Shareable via the standard Android share sheet.
Architecture
MVVM with Repository pattern throughout. Jetpack Compose for all UI (no XML layouts). Hilt for dependency injection.
ui/screens/ Compose screens (Dashboard, V2X Monitor, Sensors, Recording, Trip History, Settings…)
ui/navigation/ Navigation graph and bottom nav bar
viewmodel/ MqttViewModel, SensorViewModel, TripRecordingViewModel
data/mqtt/ MQTT repository, Paho client, exponential-backoff reconnection
data/transport/ USB tethering detection and gateway IP resolution
data/db/ Room database (sessions, trips, detected events)
data/ SensorRepository, TripRepository, CsvExporter
domain/detection/ EventDetector, RunningStats sliding window (orientation-independent)
service/ TripRecordingService (foreground service)
Connectivity
The app uses a phased transport strategy. The MQTT client, topic subscriptions, and all UI are identical across transports; only the underlying network path changes.
| Phase | Transport | Status |
|---|---|---|
| Phase 01 | Wi-Fi | Complete |
| Phase 02 | USB-C tethering | Active |
| Phase 03 | Bluetooth BLE | Future |
The MQTT broker runs on the OBU hardware (Mosquitto 2.0.11, port 1883). In Phase 02, Android USB tethering exposes the OBU as a virtual Ethernet interface at 192.168.42.x. The app auto-detects the gateway IP on plug-in.
Key dependencies
| Library | Purpose |
|---|---|
| Jetpack Compose + Material3 | UI |
| Eclipse Paho MQTT | OBU communication |
| Room | Local database |
| Hilt | Dependency injection |
| OSMDroid | Trip review map |
| DataStore | Settings persistence |
| FusedLocationProviderClient | GNSS |
Getting started
- Open in Android Studio (Hedgehog or newer).
- Connect a device running Android 10+ (API 29).
- Build and run the
appmodule. - For Phase 02 testing: plug the phone into the OBU via USB-C, enable USB tethering on the phone, and the app will detect the interface and connect automatically. Broker IP can be overridden manually in Settings → Connection.
- For standalone trip recording: no OBU required. Go to the Record tab and tap Record.
The Wi-Fi transport (Phase 01 broker at 192.168.3.202) remains available in developer builds and can be toggled in Settings → Developer.
Project context
The micrOBU project is funded under the ZIM program (BMWK) and targets micromobility users in Hamburg. The companion app offloads processing from the compact OBU hardware to the smartphone; GNSS fusion, event detection, and future antenna coordination all run on the phone to keep the OBU lightweight and power-efficient.
V2X communication uses ITS-G5 (IEEE 802.11p / DSRC) at 5.9 GHz. The app communicates with the OBU exclusively via the consider it MQTT API v6 (processed JSON messages); no ASN.1 encoding in the app.
Owner: HAW Hamburg