contracts/docs/impl/plans/Z27AG-CAPTURES.md

---
type: plan
status: ready
updated: 2026-10-12
---
# Z27AG decoding captures: what to do in the car

Recordings that let the broadcast frames be decoded: one thing changes at a time,
each change is marked, and OBD-II mode 01 values are recorded alongside as the
ground truth. Prior art and first candidates: [the prior-art report](../reports/Z27AG-CAN-PRIOR-ART.md).

## What records what

| In the session directory | From | Use |
|---|---|---|
| `can-*.log(.zst)` | the PEAK, every frame, kernel timestamps | what gets decoded; also holds every OBD request (`7DF`) and reply (`7E8`) |
| `vehicle.ndjson` | `obd-poller` via the bus | the same OBD replies as values (rpm, speed, throttle, load, MAP, MAF ~10 Hz; coolant, intake air, fuel 1 Hz); `env.timestamp` equals the reply frame's timestamp |
| `events.ndjson` | marks from the app | when each step happened |
| `gnss.ndjson` | gpsd (SIM7600) | speed and position for the drive |

## Operating the recorder from the app

- **Sessions start by themselves** when the PEAK sees traffic (ignition on) and end
  15 s after it stops. There is no start/stop button; nothing to do.
- **Marks:** the **Mark** button → a quick chip, or type in *Other* and press enter.
  A mark is stamped when the recorder receives it, on the same clock as the frames.
- **Check it landed:** the *Commands* list, at the top of the raw-messages pane (right
  side, or the lower half on a narrow screen), shows `✓ ok: mark 3 in
  000042-…`. `✗ error: no session` means no traffic yet: ignition on, PEAK plugged.
  A mark sent with the link down waits (`unacked`) and goes when it is back, with its
  delay noted in the mark.
- **OBD is working** when `engine_rpm`, `vehicle_speed_kph` and the rest appear in
  the signal list and move. If they never appear, see *If OBD stays silent*.

## Marks

Type the step number first, then what is happening: `3 brake on`, `3 brake off`.
One mark when an action starts and one when it ends is enough; a slow, steady
action between them beats a quick one. Wait about 3 s between steps.

## Checklist

**Before:** PEAK on the OBD port, Orin up, tablet connected. Engine off, doors shut.

### Parked, ignition on, engine off

| # | Do | Mark | Finds |
|---|---|---|---|
| 1 | Nothing for 20 s | `1 baseline` | the resting values of every ID |
| 2 | Accelerator: slowly to the floor over 5 s, hold 3 s, slowly back | `2 accel start` / `2 accel end` | pedal position (engine off: no rpm to confuse it) |
| 3 | Brake: press, hold 3 s, release; three times | `3 brake on` / `3 brake off` each time | brake switch, maybe pressure |
| 4 | Clutch: same, three times | `4 clutch on` / `4 clutch off` | clutch switch |
| 5 | Steering: centre → full left → full right → centre, slowly | `5 steer start` / `5 steer end` | steering angle |
| 6 | Gears: 1, 2, 3, 4, 5, R, neutral, 3 s each | `6 gear 1` … `6 gear R`, `6 neutral` | reverse switch (gear position if broadcast) |
| 7 | Handbrake up, down, up | `7 handbrake on` / `off` | handbrake switch |
| 8 | Indicator left 5 s, right 5 s, hazards 5 s | `8 left`, `8 right`, `8 hazard`, `8 off` | indicator states |
| 9 | Side lights, dipped, main beam, flash, fogs, off | one mark each | light states |
| 10 | Each door open/close, boot, bonnet | one mark each | door switches |
| 11 | Wipers int / low / high / off, washer | one mark each | wiper states |
| 12 | A/C on / off, blower up / down | one mark each | A/C request |
| 13 | Seatbelt on / off | `13 belt on` / `off` | belt switch |

### Engine running, parked

| # | Do | Mark | Finds |
|---|---|---|---|
| 14 | Cold start if possible; idle 60 s | `14 engine start` | coolant and oil warming; idle control |
| 15 | Revs in steps: hold 1500, 2000, 3000 rpm 5 s each, back to idle | `15 rpm 1500` … `15 idle` | engine speed (OBD rpm is the reference), throttle against pedal |
| 16 | Three sharp blips | `16 blips` | response timing of throttle, rpm, MAP |
| 17 | A/C on 20 s, off | `17 ac on` / `off` | compressor clutch, idle-up |
| 18 | Idle until the radiator fan cuts in, if it will | `18 fan` | fan state, coolant threshold |

### Driving (a passenger types the marks, or skip them)

| # | Do | Mark | Finds |
|---|---|---|---|
| 19 | Pull away; steady 20, 40, 60 km/h for 10 s each where safe | `19 steady 20` … (optional) | road and wheel speeds against OBD and GNSS speed |
| 20 | A gentle stop, a firmer stop | `20 stop` (optional) | brake pressure, deceleration |
| 21 | A few corners each way | — | yaw / lateral g, wheel speed differences |
| 22 | Each gear through the box | — | gear (from rpm ÷ speed if not broadcast) |

Speed needs no marks: OBD speed and GNSS speed are recorded continuously. The
drive is the important part; the parked steps can be split over several sessions.

## If OBD stays silent

`yukart/system/obd-poller` says why (visible in `mosquitto_sub -v -t 'yukart/system/#'`
on the Orin):

- `bus idle: not polling`: no traffic: ignition off or PEAK unplugged.
- `no ECU answers 01 00`: the engine ECU does not do standard mode 01 on this bus.
  Then OBDb's MUT-III (`21 xx`) requests are the next thing to try.
- To see what answers, on the Orin: `sudo systemctl stop yukart-obd-poller`,
  `yukart-obd-poller --once` (supported PIDs and one value each, with reply times),
  `sudo systemctl start yukart-obd-poller`. Never two pollers at once: their
  replies would cross.

## Afterwards

Sessions are in `/var/lib/yukart/recordings/` on the car Orin. Copy one off with
`rsync -a mikkeli-orin-nano:/var/lib/yukart/recordings/<session>/ …` into
`yukart-data`, with a line in its README of what was done.