svc-core/docs/impl/plans/INITIAL.md

type, status, updated

type	status	updated
plan	active	2026-10-09

Initial plan

Order

1. recorder — raw CAN and GNSS to disk. Built first because every later piece is developed against what it records.
2. obd-poller — standard OBD-II PIDs at a low rate, the cross-check for reverse-engineered signals. The first transmitter: can_pcan leaves listen-only for it, a deliberate step.
3. can-bridge and gnss — publish onto the broker once it exists (project-yukart Phase 3; MQTT at ~890 frames/s is still unproven).
4. decoder — frames to named signals via the DBC in contracts.

Recorder

Reads SocketCAN and gpsd directly. It is tier 1, and the broker is a single point of failure that raw capture should not share. When can-bridge exists, the recorder still owns raw capture; it subscribes to the bus only for decoded signals.

Session triggers

Trigger	Starts on	Ends on
auto	the first CAN frame	--idle (15 s) with no frames
manual	ctl start [label]	ctl stop, or shutdown

• No traffic, no session. The PEAK attached at a desk, attached to a parked car with the bus asleep, or unplugged, produces nothing — the socket is retried every second in silence.
• Cranking stays inside one session. A bus dropout or adapter re-enumeration shorter than the idle timeout is recorded as can_link events, not as a split.
• Blips are discarded. An auto session with under --min-secs (3 s) of traffic and no marks is deleted at close — door unlocks and brief plug-ins.
• ctl start during an auto session promotes it to manual. After ctl stop, auto start waits for the bus to go idle, so a stop sticks.
• ctl auto off (or --no-auto) leaves only manual sessions.

The power service planned in orin-nano-env-setup (docs/impl/plans/POWER.md) is the intended second client: ctl mark crank for a recovered input loss, and systemctl stop yukart-recorder before poweroff.

Session layout

/var/lib/yukart/recordings/
  .last-seq                    high-water mark; numbers are never reused
  000042-20261009T163736/      sequence number orders; the local time is for humans
    session.json               status open → closed | truncated; trigger, label, host,
                               boot_id, start/end realtime + monotonic + clock sync,
                               frame and drop counts, end reason
    can-0001.log.zst           candump -L, closed chunks (5 min or 64 MB), zstd
    can-0002.log               the open chunk, plain
    gnss.ndjson                {"rx": <local receive time>, "msg": <gpsd report>}
    events.ndjson              marks, can_link, gnss_link, clock_step, drops, storage_bound

zstdcat can-*.log.zst can-*.log | canplayer replays a session.

Failsafes

Failure	Behaviour
Power loss, crash, SIGKILL	open chunk is fdatasync'd every second; at the next start the session is marked truncated and its chunks compressed
Crash mid-compression	compression writes .zst.tmp then renames; the plain chunk is removed only after
Adapter unplugged, link down	reopen every second; recorded as can_link events
gpsd down	reconnect every 3 s; CAN capture unaffected
Writer slower than the bus	100 000-frame queue (~110 s); overflow counted as queue_drops
Kernel socket overflow	SO_RXQ_OVFL counted as kernel_drops
Disk filling	oldest closed sessions deleted to stay under --cap-gb (50) and above --min-free-gb (20); the open session is never deleted
Control socket fails	logged; auto capture continues

Measured on the first capture: ~33 KB/s of candump text, ~5.5 KB/s after zstd — about 20 MB per hour of driving. The 50 GB default holds years of it; the cap is there for the failure where something else fills the disk.

Time

The car unit has no RTC battery yet and can start with a stale clock that chrony steps later. CAN frames carry the kernel's receive timestamp (SO_TIMESTAMP, CLOCK_REALTIME), and GNSS reports carry their local receive time — the same clock, so CAN and GNSS line up within a session however wrong that clock is.

To get absolute time back afterwards:

• session.json records the kernel's sync state at start and end.
• clock_step events record every step over 50 ms with its size.
• Each TPV holds GNSS UTC beside its local receive time; their difference is the clock error, plus the SIM7600's NMEA latency (no PPS: expect tens to hundreds of milliseconds, constant enough to calibrate out).

At 1 Hz GNSS against ~890 frames/s, alignment to a few hundred milliseconds is what this gives. It is enough to match CAN speed against GNSS speed; it is not enough to time individual frames against position.

Open

• Session marking from the app. app-flutter's mark button reaches the recorder through svc-gw, which will forward to the control socket.
• Native builds. scripts/deploy-recorder.sh cross-compiles from the workstation while the development Orin is offline; check-glibc.sh gates it.
• Copy-off. Recordings stay on the car until the parked-at-home step in the power plan, or a manual rsync.