The Use Case app's v2x-uca/output/json topics are a rate-limited and
lossy view: traffic the OBU's radio actually heard, the ESP32's CAM
pinger among it, never reached the app. The raw v2x/rx topics carry
everything, as RecvV2XMessage protobuf with the ITS-G5 PDU in one bytes
field (CI-CiT MQTT API section 2.4).
RecvV2xMessage is a minimal protobuf wire-format reader for the three
fields needed: btpHeader type and destination port, the GeoNetworking
destination-area radius, and the payload. Hand-written for the same
reason the ASN.1 codecs are, rather than adding protoc and the protobuf
Gradle plugin and vendoring a third-party .proto into this repository.
Field numbers are pinned by a byte fixture written out by hand from the
encoding rules, not generated by our own encoder.
Raw payloads now travel as bytes rather than String. The previous UTF-8
round trip replaced every byte that is not valid UTF-8, leaving a
payload that still looked plausible in a log and decoded to nothing.
CAM, DENM and SPATEM from both transports now meet in shared handlers,
so everything downstream is transport-agnostic. SPATEM works on the CiT
One path for the first time, and DENM gains its relevance radius there.
Where both sources describe the same event the decoded one wins: remote
CAMs from the processed topic are suppressed while the raw topic is
live, and DENMs dedup on ETSI's actionID with the decoded list last.
The processed topics stay subscribed as a fallback for an OBU whose
configuration does not publish the raw ones.
Two defects found while testing this:
CamPinger transmits under a fixed bench station id, deliberately
distinct from the persisted one, but the self-heard filter only knew
the persisted id. Every ping therefore came back through the ESP32's
promiscuous receive as a remote road user sitting exactly on top of the
ego position, moving at the ego's own speed and heading, and was handed
to the detection engine as a collision partner for itself. The rule now
lives in OwnStationIds, covers both ids, and has tests, so a third
transmit path cannot reintroduce the same gap quietly.
Self-heard frames are now counted and reported on the pinger card
instead of being discarded. That round trip is the only direct evidence
the serial link, the ESP32's transmit path and its receive path all
work, which is what the bench pinger exists to demonstrate.
Also: the stationType warning banner no longer shows in ESP32-C5 mode.
It reads a value from the CiT One's obu_gnss topic, which that hardware
never publishes, so it stayed on screen reporting on an OBU that was no
longer in use.
Ashin Walpola
034ef22336