# 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.

## Toolchain: use a dedicated terminal (ESP-IDF 5.5.4)

This project builds against the **global** ESP-IDF 5.5.4, NOT the 6.1 checkout
that `obu-firmware` uses. Keep one terminal per toolchain and never export both
in the same window - the second export inherits the first's
`IDF_PYTHON_ENV_PATH` and then fails every dependency check (`click`,
`esptool`, `cryptography`, ... "not met"). That is env-var bleed, not a broken
install: do **not** run `install.bat` to "fix" it, that damages one of the two
environments.

| Terminal | Export | Project |
|---|---|---|
| Transmitter | `C:\Espressif\frameworks\esp-idf-v5.5.4\export.ps1` | this one |
| OBU | `...\micrOBU_workspace\its-g5-receiver-firmware\esp-idf\export.ps1` | `obu-firmware` |

If a terminal has already been used for the other IDF, clear the state first:

```powershell
$env:IDF_PYTHON_ENV_PATH = $null; $env:IDF_PATH = $null
```

Also note `build/` here was regenerated from scratch (its CMake cache still
referenced an older source path under `micrOBU_workspace/v2x-obu-esp32c5/`,
which makes `idf.py fullclean` refuse to run). If that error reappears, delete
`build/` manually rather than fighting it.

## CAM encoding

`main/cam.c` IS compiled here (unlike `obu-firmware`'s copy, which is a
reference only). It must stay bit-identical to `obu-firmware/main/cam.c` and
the app's `CamUperCodec.kt` - all three encode the same wire format, and a
one-bit divergence in any of them is invisible on the bench but wrong against
real equipment. See the `CurvatureCalculationMode` comment in that file.

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).