obd-poller: OBD-II mode 01, the single CAN writer; recorder keeps its values

obd-poller asks 0x7DF for the nine obd2 signals, only while the bus is alive,
and publishes envelopes stamped with the reply's kernel time. The recorder
subscribes to yukart/vehicle/* and writes vehicle.ndjson beside the frames.
Tested against a fake ECU on vcan0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

Cargo.toml

@@ -2,7 +2,7 @@
 name = "svc-core"
 version = "0.1.0"
 edition = "2021"
-description = "Acquisition and processing cluster: recorder and orin-status now; can-bridge, obd-poller, gnss, decoder later"
+description = "Acquisition and processing cluster: recorder, orin-status and obd-poller now; can-bridge, gnss, decoder later"
 publish = false
 
 [[bin]]
@@ -13,6 +13,10 @@ path = "src/recorder/main.rs"
 name = "orin-status"
 path = "src/orin-status/main.rs"
 
+[[bin]]
+name = "obd-poller"
+path = "src/obd-poller/main.rs"
+
 [[bin]]
 name = "bus-bench"
 path = "src/bus-bench/main.rs"

README.md

@@ -10,18 +10,21 @@ This file serves as the minimalist portal to other docs
 ## What this repo is about
 
 The acquisition and processing cluster on the Orin, developed and deployed as one
-unit: `recorder` and `orin-status` now; `can-bridge`, `obd-poller`, `gnss` and `decoder` as they are
+unit: `recorder`, `orin-status` and `obd-poller` now; `can-bridge`, `gnss` and `decoder` as they are
 needed.
 
 | Binary | Installed as | Does |
 |---|---|---|
-| `recorder` | `yukart-recorder.service` | Raw CAN + GNSS to disk, in sessions, under a storage bound |
+| `recorder` | `yukart-recorder.service` | Raw CAN + GNSS to disk, in sessions, under a storage bound; OBD-II values from the bus beside them |
 | `bus-bench` | not installed: a test tool | Raw CAN and decoded-signal load over MQTT, measured: loss, latency, broker CPU ([report](docs/impl/reports/BUS-BENCH.md)) |
+| `obd-poller` | `yukart-obd-poller.service` | OBD-II mode 01 polling, the single CAN writer: rpm, speed, throttle, load, MAP, MAF ~10 Hz; temperatures and fuel 1 Hz (`yukart/vehicle/*`) |
 | `orin-status` | `yukart-orin-status.service` | The Orin's health on the bus, once a second: temperatures, CPU/GPU load, memory, power, fan, WiFi/LTE/tablet links, UPS battery (`yukart/host/*`) |
 
 ```bash
 scripts/deploy-recorder.sh                 # build, glibc check, install on the car Orin
 scripts/deploy-orin-status.sh              # build on the development Orin, glibc check, install
+scripts/deploy-obd-poller.sh               # build, glibc check, install on the car Orin
+yukart-obd-poller --once                   # on the Orin, service stopped: what the ECU answers
 yukart-orin-status --once                  # on an Orin: one reading as JSON, no broker
 yukart-recorder ctl status                 # on the Orin
 yukart-recorder ctl start "cold start"     # manual session, ends only on stop

deploy/yukart-obd-poller.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=Yukart obd-poller: OBD-II mode 01 polling, the single CAN writer
+Documentation=gitea:yukart/svc-core
+# Tier 2. Ordered after the broker and nothing else: the adapter comes and goes, and
+# the poller only sends while the bus is visibly alive.
+After=mosquitto.service
+StartLimitIntervalSec=0
+
+[Service]
+User=mikkeli
+ExecStart=/usr/local/bin/yukart-obd-poller
+Restart=always
+RestartSec=2
+
+[Install]
+WantedBy=multi-user.target

docs/GUIDELINES.md

@@ -3,10 +3,13 @@ type: guidelines
 ---
 # Core services guidelines
 
-## 1. Listen-only until `obd-poller` exists
+## 1. One CAN writer: `obd-poller`
-- Nothing here opens a CAN socket for writing. The recorder only reads, and the
+- `obd-poller` is the only thing that transmits on the car's bus (project-yukart
-  host brings `can_pcan` up listen-only.  
+  decision 3): OBD-II requests, one at a time, only while the bus is visibly
-- `obd-poller` will be the single writer. Until it lands, any transmit is a bug.
+  alive. Anything else that transmits is a bug; the recorder only reads.  
+- `can_pcan` is no longer listen-only (2026-10-12), so the adapter acknowledges
+  frames like any scan tool. Going back is one line in orin-nano-env-setup's
+  `/etc/default/can-can_pcan`.
 
 ## 2. Capture never waits
 - A frame missed is gone. Producers hand frames to the writer without blocking;

docs/impl/plans/INITIAL.md

@@ -22,9 +22,10 @@ bus. Below.
 ## 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
+of failure that raw capture should not share (decision 25). When `can-bridge`
-recorder still owns raw capture; it subscribes to the bus only for decoded
+exists, the recorder still owns raw capture; it subscribes to the bus only for
-signals.
+`yukart/vehicle/*` (`--broker`, `''` to disable), and a broker that is down costs
+those envelopes, never a frame.
 
 ### Session triggers
 
@@ -60,6 +61,9 @@ is the intended second client: `ctl mark crank` for a recovered input loss, and
     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>}
+    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
     events.ndjson              marks, can_link, gnss_link, clock_step, drops, storage_bound
 ```
 
@@ -110,6 +114,35 @@ enough to time individual frames against position.
 - **Copy-off.** Recordings stay on the car until the parked-at-home step in the
   power plan, or a manual `rsync`.
 
+## 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 (~10–13 Hz each
+  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.
+
 ## orin-status
 
 The Orin's own health as envelopes on `yukart/host/<signal>`, retained, once a

scripts/deploy-obd-poller.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# Build the obd-poller for aarch64, check it against the car's glibc, and install it
+# on an Orin as the yukart-obd-poller service.
+#
+#   usage: scripts/deploy-obd-poller.sh [host]        (default: mikkeli-orin-nano)
+#
+# Cross-compiles from the workstation (the documented fallback): the development
+# Orin is the preferred native build host. Either way check-glibc.sh gates it.
+set -euo pipefail
+
+HOST="${1:-mikkeli-orin-nano}"
+cd "$(dirname "$0")/.."
+TARGET=aarch64-unknown-linux-gnu
+BIN="target/$TARGET/release/obd-poller"
+
+cargo build --release --target "$TARGET" --bin obd-poller
+scripts/check-glibc.sh "$BIN"
+
+# Binary lives under ~/infra per the host repo's guidelines; /usr/local/bin gets a symlink.
+ssh "$HOST" 'mkdir -p ~/infra/svc-core'
+scp -q "$BIN" "$HOST:infra/svc-core/obd-poller.new"
+scp -q deploy/yukart-obd-poller.service "$HOST:infra/svc-core/yukart-obd-poller.service"
+ssh "$HOST" 'set -e
+  mv ~/infra/svc-core/obd-poller.new ~/infra/svc-core/obd-poller
+  sudo ln -sfn "$HOME/infra/svc-core/obd-poller" /usr/local/bin/yukart-obd-poller
+  sudo install -m 0644 ~/infra/svc-core/yukart-obd-poller.service /etc/systemd/system/yukart-obd-poller.service
+  sudo systemctl daemon-reload
+  sudo systemctl enable yukart-obd-poller.service >/dev/null
+  sudo systemctl restart yukart-obd-poller.service
+  sleep 1
+  systemctl --no-pager --lines=5 status yukart-obd-poller.service'

scripts/deploy-recorder.sh

@@ -13,7 +13,7 @@ cd "$(dirname "$0")/.."
 TARGET=aarch64-unknown-linux-gnu
 BIN="target/$TARGET/release/recorder"
 
-cargo build --release --target "$TARGET"
+cargo build --release --target "$TARGET" --bin recorder
 scripts/check-glibc.sh "$BIN"
 
 # Binary lives under ~/infra per the host repo's guidelines; /usr/local/bin gets a symlink.

src/obd-poller/main.rs

@@ -0,0 +1,391 @@
+//! obd-poller — active OBD-II mode 01 polling, the single CAN writer (decision 3).
+//!
+//! Asks the engine ECU for standard values (SAE J1979, functional request 0x7DF,
+//! replies on 0x7E8–0x7EF) one at a time, and publishes each reply as an envelope on
+//! `yukart/vehicle/<signal>`, retained; names and units from contracts'
+//! `signals.json` (source `obd2`). The envelope's `timestamp` is the reply's kernel
+//! receive time, so it lines up with the recorder's raw frames, which hold the same
+//! request and reply. These values are the ground truth for decoding the car's own
+//! broadcast frames.
+//!
+//! It only sends while the bus is visibly alive (the interface received frames in
+//! the last second). A request into a sleeping bus gets no acknowledgement, and the
+//! adapter would retry it until it goes error-passive.
+
+mod pids;
+mod socket;
+
+use std::collections::HashMap;
+use std::process::ExitCode;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+use std::thread;
+use std::time::{Duration, Instant};
+
+use rumqttc::{Client, Event, LastWill, MqttOptions, NetworkOptions, Packet, QoS};
+use serde_json::{json, Value};
+
+use pids::{Pid, PIDS};
+use socket::ObdSocket;
+
+const USAGE: &str = "\
+usage: obd-poller [options]
+  --iface NAME         CAN interface                          (can_pcan)
+  --broker HOST:PORT   MQTT broker                            (127.0.0.1:1883)
+  --gap-ms N           pause between requests                 (10)
+  --timeout-ms N       give up on a reply after this long     (100)
+  --slow-ms N          period of the slow PIDs (temperatures, fuel) (1000)
+  --once               discover, read every supported PID once, print JSON, exit (no broker)";
+
+const REGISTRY: &str = include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/../contracts/schema/signals.json"));
+const SYSTEM_TOPIC: &str = "yukart/system/obd-poller";
+const REQUEST_ID: u32 = 0x7DF;
+
+pub fn now_us() -> i64 {
+    let d = std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).unwrap_or_default();
+    d.as_micros() as i64
+}
+
+fn mono_ns() -> i64 {
+    let mut ts: libc::timespec = unsafe { std::mem::zeroed() };
+    unsafe { libc::clock_gettime(libc::CLOCK_MONOTONIC, &mut ts) };
+    ts.tv_sec as i64 * 1_000_000_000 + ts.tv_nsec as i64
+}
+
+/// Units of the polled signals, from the registry: never authored here (contracts guideline 1).
+fn units() -> HashMap<&'static str, String> {
+    let v: Value = serde_json::from_str(REGISTRY).expect("contracts signals.json is valid JSON");
+    PIDS.iter()
+        .map(|p| {
+            let s = &v["signals"][p.signal];
+            assert_eq!(s["source"], "obd2", "signal {} is not an obd2 signal in signals.json", p.signal);
+            (p.signal, s["unit"].as_str().unwrap_or("").to_string())
+        })
+        .collect()
+}
+
+struct Opts {
+    iface: String,
+    broker: String,
+    gap: Duration,
+    timeout: Duration,
+    slow: Duration,
+    once: bool,
+}
+
+/// Is anything else talking? Received-frame count moved within the last second.
+struct BusWatch {
+    path: String,
+    last: Option<(u64, Instant)>,
+}
+
+impl BusWatch {
+    fn alive(&mut self) -> bool {
+        let Some(n) = std::fs::read_to_string(&self.path).ok().and_then(|s| s.trim().parse::<u64>().ok()) else {
+            self.last = None;
+            return false;
+        };
+        match self.last {
+            Some((prev, _)) if n != prev => self.last = Some((n, Instant::now())),
+            None => self.last = Some((n, Instant::now() - Duration::from_secs(10))),
+            _ => {}
+        }
+        self.last.map(|(_, t)| t.elapsed() < Duration::from_secs(1)).unwrap_or(false)
+    }
+}
+
+struct Poller {
+    sock: ObdSocket,
+    timeout: Duration,
+}
+
+impl Poller {
+    /// One mode 01 request; the first reply to it from any ECU: (receive time µs, ECU id, data bytes).
+    fn ask(&self, pid: u8) -> std::io::Result<Option<(i64, u32, Vec<u8>)>> {
+        self.sock.send(REQUEST_ID, &[0x02, 0x01, pid, 0x55, 0x55, 0x55, 0x55, 0x55])?;
+        let deadline = Instant::now() + self.timeout;
+        loop {
+            let left = deadline.saturating_duration_since(Instant::now());
+            if left.is_zero() {
+                return Ok(None);
+            }
+            let Some(r) = self.sock.recv(left)? else { return Ok(None) };
+            // Single frame: [length, 0x41, pid, A, B, ...]. Anything else is not our answer.
+            let len = (r.data[0] & 0x0F) as usize;
+            if r.data[0] >> 4 == 0 && len >= 2 && len <= 7 && r.data[1] == 0x41 && r.data[2] == pid {
+                return Ok(Some((r.ts_us, r.id, r.data[3..1 + len].to_vec())));
+            }
+        }
+    }
+
+    /// Supported PIDs, walking the 0x00 / 0x20 / 0x40 ... bitmasks. Empty: no ECU answered.
+    fn discover(&self) -> std::io::Result<Vec<u8>> {
+        let mut all = Vec::new();
+        let mut mask = 0x00u8;
+        loop {
+            let Some((_, _, d)) = self.ask(mask)? else { break };
+            if d.len() < 4 {
+                break;
+            }
+            let s = pids::supported_in(mask, &d);
+            let more = s.contains(&(mask + 0x20));
+            all.extend(s.into_iter().filter(|p| p % 0x20 != 0));
+            if !more || mask >= 0xC0 {
+                break;
+            }
+            mask += 0x20;
+        }
+        Ok(all)
+    }
+}
+
+fn parse() -> Result<Opts, String> {
+    let mut o = Opts {
+        iface: "can_pcan".into(),
+        broker: "127.0.0.1:1883".into(),
+        gap: Duration::from_millis(10),
+        timeout: Duration::from_millis(100),
+        slow: Duration::from_millis(1000),
+        once: false,
+    };
+    let mut args = std::env::args().skip(1);
+    while let Some(a) = args.next() {
+        if a == "--once" {
+            o.once = true;
+            continue;
+        }
+        let v = args.next().ok_or(format!("{a} needs a value"))?;
+        let ms = || v.parse::<u64>().map(Duration::from_millis).map_err(|_| format!("{a}: not a number: {v}"));
+        match a.as_str() {
+            "--iface" => o.iface = v.clone(),
+            "--broker" => o.broker = v.clone(),
+            "--gap-ms" => o.gap = ms()?,
+            "--timeout-ms" => o.timeout = ms()?,
+            "--slow-ms" => o.slow = ms()?,
+            _ => return Err(format!("unknown option {a}")),
+        }
+    }
+    Ok(o)
+}
+
+fn once(o: &Opts) -> ExitCode {
+    let mut watch = BusWatch { path: format!("/sys/class/net/{}/statistics/rx_packets", o.iface), last: None };
+    let t = Instant::now();
+    while !watch.alive() {
+        if t.elapsed() > Duration::from_secs(3) {
+            eprintln!("obd-poller: {}: no traffic; is the ignition on?", o.iface);
+            return ExitCode::FAILURE;
+        }
+        thread::sleep(Duration::from_millis(100));
+    }
+    let p = match ObdSocket::open(&o.iface) {
+        Ok(sock) => Poller { sock, timeout: o.timeout },
+        Err(e) => {
+            eprintln!("obd-poller: {}: {e}", o.iface);
+            return ExitCode::FAILURE;
+        }
+    };
+    let run = || -> std::io::Result<Value> {
+        let supported = p.discover()?;
+        let mut values = serde_json::Map::new();
+        for pid in PIDS.iter().filter(|x| supported.contains(&x.pid)) {
+            let t = Instant::now();
+            if let Some((_, ecu, d)) = p.ask(pid.pid)?.filter(|r| r.2.len() >= pid.bytes) {
+                values.insert(pid.signal.into(), json!({ "value": (pid.decode)(&d), "ecu": format!("{ecu:03X}"),
+                                                         "reply_ms": t.elapsed().as_secs_f64() * 1e3 }));
+            }
+        }
+        Ok(json!({
+            "supported": supported.iter().map(|x| format!("{x:02X}")).collect::<Vec<_>>(),
+            "values": values,
+        }))
+    };
+    match run() {
+        Ok(v) => {
+            println!("{}", serde_json::to_string_pretty(&v).unwrap());
+            ExitCode::SUCCESS
+        }
+        Err(e) => {
+            eprintln!("obd-poller: {e}");
+            ExitCode::FAILURE
+        }
+    }
+}
+
+fn main() -> ExitCode {
+    let o = match parse() {
+        Ok(o) => o,
+        Err(e) => {
+            eprintln!("obd-poller: {e}\n{USAGE}");
+            return ExitCode::from(2);
+        }
+    };
+    if o.once {
+        return once(&o);
+    }
+    let units = units();
+
+    let Some((host, port)) = o.broker.rsplit_once(':').and_then(|(h, p)| Some((h.to_string(), p.parse::<u16>().ok()?)))
+    else {
+        eprintln!("obd-poller: --broker must be HOST:PORT\n{USAGE}");
+        return ExitCode::from(2);
+    };
+    let mut opts = MqttOptions::new("obd-poller", host, port);
+    opts.set_keep_alive(Duration::from_secs(5));
+    opts.set_last_will(LastWill::new(
+        SYSTEM_TOPIC,
+        json!({ "state": "stopping", "detail": "connection lost" }).to_string(),
+        QoS::AtLeastOnce,
+        true,
+    ));
+    let (client, mut connection) = Client::new(opts, 256);
+    let mut net = NetworkOptions::new();
+    net.set_tcp_nodelay(true); // svc-core BUS-BENCH.md: Nagle adds a ~40 ms tail
+    connection.eventloop.set_network_options(net);
+    let connected = Arc::new(AtomicBool::new(false));
+    let announce = Arc::new(AtomicBool::new(false));
+    {
+        let (connected, announce) = (connected.clone(), announce.clone());
+        thread::spawn(move || {
+            for ev in connection.iter() {
+                match ev {
+                    Ok(Event::Incoming(Packet::ConnAck(_))) => {
+                        eprintln!("obd-poller: connected to the broker");
+                        connected.store(true, Ordering::Relaxed);
+                        announce.store(true, Ordering::Relaxed);
+                    }
+                    Ok(_) => {}
+                    Err(e) => {
+                        if connected.swap(false, Ordering::Relaxed) {
+                            eprintln!("obd-poller: broker: {e}; retrying");
+                        }
+                        thread::sleep(Duration::from_secs(1));
+                    }
+                }
+            }
+        });
+    }
+
+    eprintln!("obd-poller {} on {}, publishing to {}", env!("CARGO_PKG_VERSION"), o.iface, o.broker);
+    let mut watch = BusWatch { path: format!("/sys/class/net/{}/statistics/rx_packets", o.iface), last: None };
+    let mut poller: Option<Poller> = None;
+    let mut supported: Option<Vec<u8>> = None;
+    let mut last_slow = Instant::now() - o.slow;
+    let mut next_discover = Instant::now();
+    let mut counts: HashMap<&'static str, u32> = HashMap::new();
+    let mut misses = 0u32;
+    let mut window = Instant::now();
+    let mut state = json!({ "state": "starting" });
+    let mut last_state = String::new();
+    let mut last_announce = Instant::now();
+
+    loop {
+        // The service's own state: on change, on reconnect, and every 5 s with the achieved rates.
+        let s = state.to_string();
+        if connected.load(Ordering::Relaxed)
+            && (s != last_state || announce.swap(false, Ordering::Relaxed) || last_announce.elapsed() > Duration::from_secs(5))
+        {
+            // Log transitions only; the rates change every 5 s.
+            let kind = |j: &str| serde_json::from_str::<Value>(j).ok().map(|v| (v["state"].clone(), v["detail"].is_string().then(|| v["detail"].clone())));
+            if kind(&s) != kind(&last_state) {
+                eprintln!("obd-poller: {s}");
+            }
+            let _ = client.try_publish(SYSTEM_TOPIC, QoS::AtLeastOnce, true, s.clone());
+            last_state = s;
+            last_announce = Instant::now();
+        }
+
+        if !watch.alive() {
+            // Asleep, ignition off, or unplugged: say nothing on the bus, and rediscover once it wakes.
+            poller = None;
+            supported = None;
+            state = json!({ "state": "degraded", "detail": "bus idle: not polling" });
+            thread::sleep(Duration::from_millis(250));
+            continue;
+        }
+        if poller.is_none() {
+            match ObdSocket::open(&o.iface) {
+                Ok(sock) => poller = Some(Poller { sock, timeout: o.timeout }),
+                Err(e) => {
+                    state = json!({ "state": "degraded", "detail": format!("{}: {e}", o.iface) });
+                    thread::sleep(Duration::from_secs(1));
+                    continue;
+                }
+            }
+        }
+        let p = poller.as_ref().unwrap();
+
+        if supported.is_none() {
+            if Instant::now() < next_discover {
+                thread::sleep(Duration::from_millis(100));
+                continue;
+            }
+            match p.discover() {
+                Ok(s) if !s.is_empty() => {
+                    let polled: Vec<&str> = PIDS.iter().filter(|x| s.contains(&x.pid)).map(|x| x.signal).collect();
+                    eprintln!("obd-poller: supported PIDs {:02X?}; polling {polled:?}", s);
+                    supported = Some(s);
+                    misses = 0;
+                }
+                Ok(_) => {
+                    state = json!({ "state": "degraded", "detail": "no ECU answers 01 00; retrying in 5 s" });
+                    next_discover = Instant::now() + Duration::from_secs(5);
+                }
+                Err(e) => {
+                    state = json!({ "state": "degraded", "detail": format!("{}: {e}", o.iface) });
+                    poller = None;
+                    next_discover = Instant::now() + Duration::from_secs(1);
+                }
+            }
+            continue;
+        }
+
+        // One round: the fast PIDs, and the slow ones when their period is up.
+        let slow_due = last_slow.elapsed() >= o.slow;
+        if slow_due {
+            last_slow = Instant::now();
+        }
+        let sup = supported.as_ref().unwrap();
+        let round: Vec<&Pid> = PIDS.iter().filter(|x| sup.contains(&x.pid) && (x.fast || slow_due)).collect();
+        let mut failed = false;
+        for pid in round {
+            match p.ask(pid.pid) {
+                Ok(Some((ts, _, d))) if d.len() >= pid.bytes => {
+                    *counts.entry(pid.signal).or_default() += 1;
+                    if connected.load(Ordering::Relaxed) {
+                        let v = (pid.decode)(&d);
+                        let env = json!({ "timestamp": ts, "monotonic": mono_ns(),
+                                          "value": (v * 100.0).round() / 100.0, "unit": units[pid.signal] });
+                        let _ = client.try_publish(format!("yukart/vehicle/{}", pid.signal), QoS::AtMostOnce, true, env.to_string());
+                    }
+                }
+                Ok(_) => misses += 1,
+                Err(e) => {
+                    // ENOBUFS (tx queue full: nothing acknowledges), ENETDOWN, ENODEV.
+                    state = json!({ "state": "degraded", "detail": format!("{}: {e}", o.iface) });
+                    poller = None;
+                    failed = true;
+                    thread::sleep(Duration::from_millis(500));
+                    break;
+                }
+            }
+            thread::sleep(o.gap);
+        }
+        if failed {
+            continue;
+        }
+
+        if window.elapsed() >= Duration::from_secs(5) {
+            let secs = window.elapsed().as_secs_f64();
+            let rates: serde_json::Map<String, Value> =
+                counts.iter().map(|(k, n)| (k.to_string(), json!((*n as f64 / secs * 10.0).round() / 10.0))).collect();
+            // An odd unanswered request is normal; none answered at all is not.
+            state = json!({ "state": if counts.is_empty() { "degraded" } else { "ready" },
+                            "detail": { "supported": sup.iter().map(|x| format!("{x:02X}")).collect::<Vec<_>>(),
+                                        "rates_hz": rates, "unanswered": misses } });
+            counts.clear();
+            misses = 0;
+            window = Instant::now();
+        }
+    }
+}

src/obd-poller/pids.rs

@@ -0,0 +1,59 @@
+//! The OBD-II mode 01 PIDs polled, and how each reply becomes a value (SAE J1979).
+//! Signal names and units belong to contracts' `signals.json` (source `obd2`).
+
+pub struct Pid {
+    pub pid: u8,
+    pub signal: &'static str,
+    /// Reply data bytes A, B, ... needed.
+    pub bytes: usize,
+    pub decode: fn(&[u8]) -> f64,
+    /// Polled every round; the rest about once a second.
+    pub fast: bool,
+}
+
+fn ab(d: &[u8]) -> f64 {
+    (d[0] as f64) * 256.0 + d[1] as f64
+}
+
+pub const PIDS: &[Pid] = &[
+    Pid { pid: 0x0C, signal: "engine_rpm", bytes: 2, decode: |d| ab(d) / 4.0, fast: true },
+    Pid { pid: 0x0D, signal: "vehicle_speed_kph", bytes: 1, decode: |d| d[0] as f64, fast: true },
+    Pid { pid: 0x11, signal: "throttle_pct", bytes: 1, decode: |d| d[0] as f64 * 100.0 / 255.0, fast: true },
+    Pid { pid: 0x04, signal: "engine_load_pct", bytes: 1, decode: |d| d[0] as f64 * 100.0 / 255.0, fast: true },
+    Pid { pid: 0x0B, signal: "intake_pressure_kpa", bytes: 1, decode: |d| d[0] as f64, fast: true },
+    Pid { pid: 0x10, signal: "maf_gps", bytes: 2, decode: |d| ab(d) / 100.0, fast: true },
+    Pid { pid: 0x05, signal: "coolant_temp_c", bytes: 1, decode: |d| d[0] as f64 - 40.0, fast: false },
+    Pid { pid: 0x0F, signal: "intake_air_temp_c", bytes: 1, decode: |d| d[0] as f64 - 40.0, fast: false },
+    Pid { pid: 0x2F, signal: "fuel_level_pct", bytes: 1, decode: |d| d[0] as f64 * 100.0 / 255.0, fast: false },
+];
+
+/// The bitmask PIDs (0x00, 0x20, ...): bit 7 of byte A is the PID one above the mask's own.
+pub fn supported_in(mask_pid: u8, d: &[u8]) -> Vec<u8> {
+    let bits = u32::from_be_bytes([d[0], d[1], d[2], d[3]]);
+    (0..32).filter(|i| bits & (1 << (31 - i)) != 0).map(|i| mask_pid + 1 + i as u8).collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn by(pid: u8) -> &'static Pid {
+        PIDS.iter().find(|p| p.pid == pid).unwrap()
+    }
+
+    #[test]
+    fn decodes_j1979_examples() {
+        assert_eq!((by(0x0C).decode)(&[0x0D, 0x34]), 845.0); // 0x0D34 / 4
+        assert_eq!((by(0x05).decode)(&[0x7B]), 83.0);
+        assert_eq!((by(0x10).decode)(&[0x01, 0xF4]), 5.0);
+        assert!(((by(0x11).decode)(&[0xFF]) - 100.0).abs() < 1e-9);
+    }
+
+    #[test]
+    fn reads_the_supported_bitmask() {
+        // 0xBE1FA813: a common real-world reply to 01 00.
+        let s = supported_in(0x00, &[0xBE, 0x1F, 0xA8, 0x13]);
+        assert_eq!(&s[..6], &[0x01, 0x03, 0x04, 0x05, 0x06, 0x07]);
+        assert!(s.contains(&0x0C) && s.contains(&0x0D) && s.contains(&0x20));
+    }
+}

src/obd-poller/socket.rs

@@ -0,0 +1,110 @@
+//! A SocketCAN socket for OBD-II request/response: sends requests, and receives only
+//! the diagnostic response IDs (0x7E8–0x7EF), each with the kernel's receive time.
+//!
+//! The bus's own ~900 frames/s never reach this process: the kernel filter drops
+//! them. Other sockets on the interface (the recorder) still see the requests sent
+//! here, through SocketCAN's local loopback, and the ECU's replies.
+
+use std::ffi::CString;
+use std::io;
+use std::mem::{size_of, zeroed};
+use std::time::Duration;
+
+pub struct Response {
+    /// CLOCK_REALTIME at reception, microseconds.
+    pub ts_us: i64,
+    pub id: u32,
+    pub data: [u8; 8],
+}
+
+pub struct ObdSocket {
+    fd: i32,
+}
+
+impl Drop for ObdSocket {
+    fn drop(&mut self) {
+        unsafe { libc::close(self.fd) };
+    }
+}
+
+fn setopt<T>(fd: i32, level: i32, name: i32, val: &T) -> io::Result<()> {
+    let r = unsafe {
+        libc::setsockopt(fd, level, name, val as *const T as *const libc::c_void, size_of::<T>() as u32)
+    };
+    if r < 0 { Err(io::Error::last_os_error()) } else { Ok(()) }
+}
+
+impl ObdSocket {
+    pub fn open(iface: &str) -> io::Result<Self> {
+        let name = CString::new(iface).map_err(|e| io::Error::new(io::ErrorKind::InvalidInput, e))?;
+        let idx = unsafe { libc::if_nametoindex(name.as_ptr()) };
+        if idx == 0 {
+            return Err(io::Error::last_os_error());
+        }
+        let fd = unsafe { libc::socket(libc::PF_CAN, libc::SOCK_RAW | libc::SOCK_CLOEXEC, libc::CAN_RAW) };
+        if fd < 0 {
+            return Err(io::Error::last_os_error());
+        }
+        let sock = ObdSocket { fd };
+        // Standard 11-bit IDs 0x7E8..0x7EF only: the eight possible ECU responders.
+        let filter = libc::can_filter { can_id: 0x7E8, can_mask: 0x7F8 | libc::CAN_EFF_FLAG | libc::CAN_RTR_FLAG };
+        setopt(fd, libc::SOL_CAN_RAW, libc::CAN_RAW_FILTER, &filter)?;
+        setopt(fd, libc::SOL_SOCKET, libc::SO_TIMESTAMP, &1i32)?;
+        let mut addr: libc::sockaddr_can = unsafe { zeroed() };
+        addr.can_family = libc::AF_CAN as u16;
+        addr.can_ifindex = idx as i32;
+        let r = unsafe {
+            libc::bind(fd, &addr as *const _ as *const libc::sockaddr, size_of::<libc::sockaddr_can>() as u32)
+        };
+        if r < 0 {
+            return Err(io::Error::last_os_error());
+        }
+        Ok(sock)
+    }
+
+    pub fn send(&self, id: u32, data: &[u8; 8]) -> io::Result<()> {
+        let mut f: libc::can_frame = unsafe { zeroed() };
+        f.can_id = id;
+        f.can_dlc = 8;
+        f.data = *data;
+        let n = unsafe { libc::write(self.fd, &f as *const _ as *const libc::c_void, size_of::<libc::can_frame>()) };
+        if n < 0 { Err(io::Error::last_os_error()) } else { Ok(()) }
+    }
+
+    /// The next response within `timeout`, or None.
+    pub fn recv(&self, timeout: Duration) -> io::Result<Option<Response>> {
+        let tv = libc::timeval { tv_sec: timeout.as_secs() as _, tv_usec: timeout.subsec_micros().max(1) as _ };
+        setopt(self.fd, libc::SOL_SOCKET, libc::SO_RCVTIMEO, &tv)?;
+        let mut frame: libc::can_frame = unsafe { zeroed() };
+        let mut iov = libc::iovec {
+            iov_base: &mut frame as *mut _ as *mut libc::c_void,
+            iov_len: size_of::<libc::can_frame>(),
+        };
+        let mut cbuf = [0u64; 8];
+        let mut msg: libc::msghdr = unsafe { zeroed() };
+        msg.msg_iov = &mut iov;
+        msg.msg_iovlen = 1;
+        msg.msg_control = cbuf.as_mut_ptr() as *mut libc::c_void;
+        msg.msg_controllen = size_of::<[u64; 8]>() as _;
+        let n = unsafe { libc::recvmsg(self.fd, &mut msg, 0) };
+        if n < 0 {
+            let e = io::Error::last_os_error();
+            return match e.kind() {
+                io::ErrorKind::WouldBlock | io::ErrorKind::TimedOut | io::ErrorKind::Interrupted => Ok(None),
+                _ => Err(e),
+            };
+        }
+        let mut ts_us = crate::now_us();
+        unsafe {
+            let mut c = libc::CMSG_FIRSTHDR(&msg);
+            while !c.is_null() {
+                if (*c).cmsg_level == libc::SOL_SOCKET && (*c).cmsg_type == libc::SCM_TIMESTAMP {
+                    let tv = std::ptr::read_unaligned(libc::CMSG_DATA(c) as *const libc::timeval);
+                    ts_us = tv.tv_sec as i64 * 1_000_000 + tv.tv_usec as i64;
+                }
+                c = libc::CMSG_NXTHDR(&msg, c);
+            }
+        }
+        Ok(Some(Response { ts_us, id: frame.can_id & libc::CAN_SFF_MASK, data: frame.data }))
+    }
+}

src/recorder/main.rs

@@ -1,7 +1,9 @@
 //! recorder — persists raw CAN and GNSS to disk, session by session.
 //!
 //! Reads SocketCAN and gpsd directly, not through the broker: capture is tier 1 and
-//! must not depend on anything that can be late or down.
+//! must not depend on anything that can be late or down (decision 25). Envelopes on
+//! `yukart/vehicle/*` (OBD-II replies, later decoded signals) come from the broker
+//! and are recorded when it is there.
 //!
 //! Sessions start when CAN frames arrive (auto) or on `ctl start` (manual), and an
 //! auto session ends after `--idle` seconds without frames: ignition off, adapter
@@ -35,6 +37,7 @@ usage:
       --iface NAME        CAN interface               (can_pcan)
       --root DIR          recordings directory        (/var/lib/yukart/recordings)
       --gpsd HOST:PORT    gpsd, '' to disable         (127.0.0.1:2947)
+      --broker HOST:PORT  MQTT, for yukart/vehicle/*; '' to disable (127.0.0.1:1883)
       --ctl PATH          control socket              (/run/yukart-recorder/ctl.sock)
       --idle SECS         end an auto session after this long without frames (15)
       --min-secs SECS     discard auto sessions shorter than this with no marks (3)
@@ -50,6 +53,7 @@ struct Config {
     iface: String,
     root: PathBuf,
     gpsd: String,
+    broker: String,
     ctl: String,
     idle: Duration,
     min_secs: u64,
@@ -63,6 +67,7 @@ fn parse_run(args: &[String]) -> Result<Config, String> {
         iface: "can_pcan".into(),
         root: "/var/lib/yukart/recordings".into(),
         gpsd: "127.0.0.1:2947".into(),
+        broker: "127.0.0.1:1883".into(),
         ctl: "/run/yukart-recorder/ctl.sock".into(),
         idle: Duration::from_secs(15),
         min_secs: 3,
@@ -82,6 +87,7 @@ fn parse_run(args: &[String]) -> Result<Config, String> {
             "--iface" => c.iface = v.clone(),
             "--root" => c.root = v.into(),
             "--gpsd" => c.gpsd = v.clone(),
+            "--broker" => c.broker = v.clone(),
             "--ctl" => c.ctl = v.clone(),
             "--idle" => c.idle = Duration::from_secs(num()?),
             "--min-secs" => c.min_secs = num()?,
@@ -139,6 +145,7 @@ struct Recorder {
     last_tpv: Option<(f64, String)>,
     can_link: (bool, String),
     gnss_link: (bool, String),
+    bus_link: (bool, String),
     kernel_drops: u64,
     queue_drops: Arc<AtomicU64>,
     queue_drops_seen: u64,
@@ -156,6 +163,7 @@ impl Recorder {
         }
         let _ = s.event("can_link", json!({ "up": self.can_link.0, "detail": self.can_link.1 }));
         let _ = s.event("gnss_link", json!({ "up": self.gnss_link.0, "detail": self.gnss_link.1 }));
+        let _ = s.event("bus_link", json!({ "up": self.bus_link.0, "detail": self.bus_link.1 }));
         if let Some((rx, line)) = &self.last_tpv {
             let _ = s.gnss(*rx, line, true);
         }
@@ -192,6 +200,7 @@ impl Recorder {
                     "can": { "up": self.can_link.0, "detail": self.can_link.1,
                              "last_frame_age_s": self.last_frame.map(|t| t.elapsed().as_secs_f64()) },
                     "gnss": { "up": self.gnss_link.0, "detail": self.gnss_link.1 },
+                    "bus": { "up": self.bus_link.0, "detail": self.bus_link.1 },
                     "storage": { "root": self.cfg.root, "used_bytes": storage::usage(&self.cfg.root),
                                  "free_bytes": storage::free_bytes(&self.cfg.root),
                                  "cap_bytes": self.cfg.bound.cap_bytes },
@@ -282,6 +291,18 @@ impl Recorder {
                     let _ = s.event("gnss_link", json!({ "up": up, "detail": detail }));
                 }
             }
+            Event::Vehicle(rx, signal, payload, retained) => {
+                if let Some(s) = &mut self.session {
+                    let _ = s.vehicle(rx, &signal, &payload, retained);
+                }
+            }
+            Event::BusLink(up, detail) => {
+                eprintln!("bus: {detail}");
+                self.bus_link = (up, detail.clone());
+                if let Some(s) = &mut self.session {
+                    let _ = s.event("bus_link", json!({ "up": up, "detail": detail }));
+                }
+            }
             Event::Ctl(cmd, reply) => {
                 let out = self.ctl(&cmd);
                 let _ = reply.send(out);
@@ -316,6 +337,9 @@ fn run(cfg: Config) -> ExitCode {
     if !cfg.gpsd.is_empty() {
         sources::spawn_gnss(cfg.gpsd.clone(), tx.clone(), stop.clone());
     }
+    if !cfg.broker.is_empty() {
+        sources::spawn_bus(cfg.broker.clone(), tx.clone(), stop.clone());
+    }
     if let Some(dir) = Path::new(&cfg.ctl).parent() {
         let _ = std::fs::create_dir_all(dir);
     }
@@ -336,6 +360,7 @@ fn run(cfg: Config) -> ExitCode {
         last_tpv: None,
         can_link: (false, "not yet opened".into()),
         gnss_link: (false, "not yet connected".into()),
+        bus_link: (false, "not yet connected".into()),
         kernel_drops: 0,
         queue_drops,
         queue_drops_seen: 0,

src/recorder/session.rs

@@ -6,6 +6,7 @@
 //!   can-0001.log.zst    candump -L text, closed chunks compressed
 //!   can-0002.log        the open chunk, plain text, fdatasync'd every second
 //!   gnss.ndjson         every gpsd report, with the local receive time
+//!   vehicle.ndjson      every envelope on yukart/vehicle/* (OBD-II replies now, decoded signals later)
 //!   events.ndjson       marks, clock steps, link changes, drops
 //! ```
 //!
@@ -42,6 +43,7 @@ pub struct Session {
     chunk_bytes: u64,
     can: BufWriter<File>,
     gnss: BufWriter<File>,
+    vehicle: BufWriter<File>,
     events: BufWriter<File>,
     line: String,
     pub frames: u64,
@@ -118,6 +120,7 @@ impl Session {
         let s = Session {
             can: append(&dir.join(chunk_name(1)))?,
             gnss: append(&dir.join("gnss.ndjson"))?,
+            vehicle: append(&dir.join("vehicle.ndjson"))?,
             events: append(&dir.join("events.ndjson"))?,
             dir, name, trigger, meta,
             iface: iface.to_string(),
@@ -156,6 +159,17 @@ impl Session {
         writeln!(self.gnss, "{v}")
     }
 
+    /// One envelope from the bus. `retained`: the broker's stored copy, delivered on
+    /// (re)subscribe, which may predate this session.
+    pub fn vehicle(&mut self, rx: f64, signal: &str, payload: &str, retained: bool) -> io::Result<()> {
+        let env = serde_json::from_str::<Value>(payload).unwrap_or_else(|_| Value::String(payload.to_string()));
+        let mut v = json!({ "rx": rx, "signal": signal, "env": env });
+        if retained {
+            v["retained"] = json!(true);
+        }
+        writeln!(self.vehicle, "{v}")
+    }
+
     pub fn event(&mut self, kind: &str, mut extra: Value) -> io::Result<()> {
         if !extra.is_object() {
             extra = json!({});
@@ -181,6 +195,7 @@ impl Session {
     pub fn sync(&mut self) -> io::Result<()> {
         sync(&mut self.can)?;
         sync(&mut self.gnss)?;
+        sync(&mut self.vehicle)?;
         sync(&mut self.events)
     }
 

src/recorder/sources.rs

@@ -21,6 +21,9 @@ pub enum Event {
     CanLink(bool, String),
     Gnss(f64, String),
     GnssLink(bool, String),
+    /// An envelope on yukart/vehicle/<signal>: receive time, signal, payload, retained.
+    Vehicle(f64, String, String, bool),
+    BusLink(bool, String),
     Ctl(String, mpsc::Sender<String>),
 }
 
@@ -124,6 +127,48 @@ pub fn spawn_gnss(addr: String, tx: SyncSender<Event>, stop: Arc<AtomicBool>) {
     }).expect("spawn gnss thread");
 }
 
+/// Envelopes from the broker, for the record only: raw capture never waits on this.
+pub fn spawn_bus(addr: String, tx: SyncSender<Event>, stop: Arc<AtomicBool>) {
+    let Some((host, port)) = addr.rsplit_once(':').and_then(|(h, p)| Some((h.to_string(), p.parse::<u16>().ok()?))) else {
+        let _ = tx.send(Event::BusLink(false, format!("bad broker address {addr}")));
+        return;
+    };
+    thread::Builder::new().name("bus".into()).spawn(move || {
+        let mut opts = rumqttc::MqttOptions::new("recorder", host, port);
+        opts.set_keep_alive(Duration::from_secs(5));
+        let (client, mut connection) = rumqttc::Client::new(opts, 64);
+        let mut net = rumqttc::NetworkOptions::new();
+        net.set_tcp_nodelay(true);
+        connection.eventloop.set_network_options(net);
+        let mut up = false;
+        for ev in connection.iter() {
+            if stop.load(Ordering::Relaxed) {
+                return;
+            }
+            match ev {
+                Ok(rumqttc::Event::Incoming(rumqttc::Packet::ConnAck(_))) => {
+                    up = true;
+                    let _ = client.try_subscribe("yukart/vehicle/+", rumqttc::QoS::AtMostOnce);
+                    let _ = tx.send(Event::BusLink(true, format!("{addr}: subscribed to yukart/vehicle/+")));
+                }
+                Ok(rumqttc::Event::Incoming(rumqttc::Packet::Publish(p))) => {
+                    let signal = p.topic.rsplit('/').next().unwrap_or_default().to_string();
+                    let payload = String::from_utf8_lossy(&p.payload).into_owned();
+                    // Never block the event loop on the writer; CAN frames have priority in the queue.
+                    let _ = tx.try_send(Event::Vehicle(clock::realtime(), signal, payload, p.retain));
+                }
+                Ok(_) => {}
+                Err(e) => {
+                    if std::mem::take(&mut up) {
+                        let _ = tx.send(Event::BusLink(false, format!("{addr}: {e}")));
+                    }
+                    thread::sleep(Duration::from_secs(1));
+                }
+            }
+        }
+    }).expect("spawn bus thread");
+}
+
 /// One command per connection, one reply line back.
 pub fn spawn_ctl(path: String, tx: SyncSender<Event>) -> std::io::Result<()> {
     let _ = std::fs::remove_file(&path);