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---
type: plan
status: active
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updated: 2026-10-12
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---
# 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` .
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Alongside: * * `orin-status` ** — in place (2026-10-12), the first publisher on the
bus. Below.
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## Recorder
Reads SocketCAN and gpsd directly. It is tier 1, and the broker is a single point
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of failure that raw capture should not share (decision 25). When `can-bridge`
exists, the recorder still owns raw capture; it subscribes to the bus only for
`yukart/vehicle/*` (`--broker` , `''` to disable), and a broker that is down costs
those envelopes, never a frame.
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### 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>}
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vehicle.ndjson {"rx": …, "signal": …, "env": <envelope>} for every message on
yukart/vehicle/* (OBD-II now); "retained": true for the
broker's stored copy, which may predate the session
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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` .
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## obd-poller
OBD-II mode 01 (SAE J1979) on `can_pcan` , the single CAN writer. Tier 2.
- **Requests** go to the functional address `0x7DF` , one at a time; the first
single-frame reply from `0x7E8` – `0x7EF` answers it (kernel filter: nothing else
reaches the process). 100 ms timeout, 10 ms between requests.
- **Discovery** walks the supported-PID bitmasks (`01 00` , `01 20` , …) whenever the
bus wakes; only supported PIDs are polled.
- **Schedule:** rpm, speed, throttle, load, MAP and MAF every round (~10–
with a 4 ms ECU); coolant, intake air and fuel level once a second.
- **Only while the bus is alive:** the interface's received-frame count moved in
the last second. A request into a sleeping bus gets no ACK, and the adapter would
resend it until error-passive.
- **Output:** envelopes on `yukart/vehicle/<signal>` , retained; names, units and the
`obd2` source checked against contracts at build. `timestamp` is the reply's
kernel receive time, identical to its line in the recorder's CAN log.
- **State** on `yukart/system/obd-poller` : `ready` with supported PIDs, achieved
rates and unanswered count every 5 s; `degraded` with the reason (bus idle, no
ECU answers, interface errors); last will `stopping` .
- `--once` : discover, read each supported PID once, print JSON with reply times.
- **Not yet:** multi-frame replies (ISO-TP flow control), so no DTC reading (modes
03/07/0A) and no MUT-III `21 xx` requests. The kernel has no `can-isotp` ; flow
control will be done by hand.
Tested 2026-10-12 against a fake ECU on `vcan0` : 7 PIDs discovered and polled,
540 requests and 540 replies in the recorder's log, every envelope's timestamp
equal to its reply frame's.
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## orin-status
The Orin's own health as envelopes on `yukart/host/<signal>` , retained, once a
second; names and units from contracts `signals.json` (source `host` ). Tier 2,
ordered after the broker only.
| Group | Source |
|---|---|
| Temperatures | thermal zones `cpu` , `gpu` , `soc*` (hottest), `tj` ; the `cv*` zones read EAGAIN while the vision accelerators are off and are skipped |
| Load and memory | `/proc/stat` , the GPU's `load` (tenths of a percent), `/proc/meminfo` (one pool for CPU and GPU) |
| Power and fan | onboard INA3221 `VDD_IN` ; `pwm_tach` |
| Network | `/sys/class/net` counters → kbit/s; WiFi level from `/proc/net/wireless` ; the modem from `mmcli -m any -J` every 5 s on its own thread; the tablet link is carrier on `usb0` /`usb1` , counted on `l4tbr0` |
| UPS | INA219 on `/dev/i2c-7` `0x41` , below |
- A reading that fails is not published. Its retained value ages and `svc-gw`
shows it stale.
- Service state on `yukart/system/orin-status` : `ready` , or `degraded` with the
failed sources; last will `stopping` .
### UPS battery
- **Read-only.** Only register pointers are ever written; the INA219 stays at its
power-on configuration. Current is shunt voltage (10 µV per bit) over 0.01 Ω
(Waveshare's demo code), positive when charging. Bus voltage is 4 mV per bit.
- **State:** `charging` above +50 mA, `discharging` below −
input lost), `idle` between.
- **Charge** is an estimate from a 21700 resting-voltage table per cell, the
reading corrected by the pack's I·R drop (0.15 Ω, a rough figure) and smoothed.
Waveshare's demo maps 9.0–
Steadiest at rest on input power, least reliable while charging.
- The ignition-off policy (orin-nano-env-setup `docs/impl/plans/POWER.md` ) needs
the same readings. It should take them from here, or live here, rather than
open the INA219 a second time.
