MicrOBU/obu-firmware/NOTES.md

# obu-firmware

## Since 2026-09-23: signed ITS on vanetza-idf

This firmware is a port of the colleague's standalone ESP32-C5 VRU station
(`microbu-esp32c5/firmware`, its own git repository kept beside this one and gitignored here).
From it: the vanetza-idf C-ITS stack (BTP, GeoNetworking, the TS 103 097 security entity with
credentials in NVS), the station-link protocol v1 (`link_protocol.*`, `link_service.*`) over the
native USB port (`serial_link.*`, frame type 0x10 in the same 0xAA55 framing as before) and over BLE
GATT (`simple_ble.*`), and the radio adapter (`c5_radio.*`, `otm_tx_custom.c`). Build with ESP-IDF
**6.0.2**; see FLASHING.md.

The phone builds CAM or VAM, configures the station, provisions credentials, sends PoTi and hands
each message over as a BTP-DATA.request; the firmware adds GN/BTP, signs with the authorization
ticket, and transmits. The phone side is `Esp32Link.kt` in the app.

Changed or added for this project (search for `MicrOBU:` in the sources):

- **Reception stays as it was.** vanetza-idf decapsulates with `itsGnSnDecapResultHandling =
  STRICT`, so it drops unsigned traffic (the bench sim car) and everything signed under a root other
  than the provisioned demo root (every RSU). Every captured frame therefore also goes through the
  previous firmware's `gn_unwrap.c` and reaches the phone as link opcode `V2X_RX` (0x85), whose body
  is exactly the old `SERIAL_MSG_V2X_RX` payload (`Station::forward_raw`). The app's receive side is
  unchanged.
- **Unsigned transmission is still possible.** The colleague's station refuses unsecured requests.
  Here a request with GN security profile 1 goes out with the previous firmware's `geonet.c` header
  and the position of the last PoTi (`Station::unsecured_request`); the app's "Sign outgoing
  messages" setting decides per message.
- **Console on UART0.** ESP_LOG stays on the CH343 bridge port (COM3 on the bench); the native port
  carries only link frames. The colleague's single-port board routes the log into LOG frames there
  (`CONFIG_MICROBU_LOG_OVER_LINK`, off here).
- **BLE pauses while USB is in use** (`CONFIG_MICROBU_BLE_USB_IDLE_MS`, 3 s): BLE and ITS-G5 share
  the C5's one RF front end. Whether a live BLE connection disturbs 5.9 GHz is still unmeasured
  (TODO.md).
- A serial write no longer stalls the station task when no USB host is present (BLE-only use).
- A notification longer than the ATT MTU is dropped instead of silently truncated.
- The Wi-Fi RX callback's 2.4 KB capture buffer is static rather than on the driver task's stack
  (the previous firmware's commit 04b0076 fixed the same risk).
- Manual country policy and the TX-power read-back from the previous firmware's radio bring-up.
- The activity LED (GPIO27 on the colleague's XIAO board) is off unless configured.

Credentials: the app ships `assets/demo-chain.vcr`, a throwaway chain generated 2026-09-23 with the
colleague's `vidf_issue` (root `6E7D0374FB021901`, AA `B3312F29844299E0`, AT `B80B49387A4C12EB`
valid two years, permissions psid 36 SSP `010000` and psid 638 SSP `01`). The colleague's own demo
chain only grants psid 638 and so cannot sign CAMs. Not EU-registered: receivers that verify against
the EU trust list drop what it signs.

Time: the signature's generationTime comes from the PoTi timestamp, which follows the app's
`ItsTime` convention (UTC-based, no leap seconds). The colleague's VBS adds the 5 leap seconds.
Which one is right is the open question documented in `ItsTime.kt`.

## Earlier notes (Phase 2, superseded)

### OBU transmit firmware - Phase 2 (in progress: HLN-SV DENM beacon)

Started. See `docs/04-transmit-setup.md` in the project root for build/flash
steps and how to validate this against your own sniffer.

Implements one profile so far: **HLN-SV** (aftermarket stationary recovery
vehicle), causeCode 94 (stationaryVehicle), subCauseCode 0, active while the
hazard-light GPIO is grounded. No location/alacarte containers.

- `main/main.c` - entry point, the `phy_11p_set`/`phy_change_channel(5900,...)`
  register hack, GPIO polling, TX loop
- `main/denm.c` / `.h` - ASN.1 UPER encoding of a minimal DENM
- `main/geonet.c` / `.h` - GeoNetworking Basic/Common/SHB headers + BTP-B
- `main/dot11p.c` / `.h` - 802.11 OCB (QoS Data, broadcast) frame + LLC/SNAP

Known gaps, tracked as TODOs in the source: no real GNSS (lat/long hardcoded
0), no real time source (detectionTime/referenceTime hardcoded 0, decodes as
2004-01-01), fixed (non-rotating) pseudonym MAC, SHB instead of GeoBroadcast
(no multi-hop forwarding), unsecured (no IEEE 1609.2 signing).