Pin each SDR service to a dongle by serial; OP25 always opens its SDR by serial

Fixes node-26#11. OP25's generated config said "rtl" (= whichever dongle
enumerates first), so on 2-SDR nodes a decoder could take OP25's dongle
and stop recording. Now:

- sdr_pins: {op25|adsb|ais: serial}, absent = automatic. Every OP25
  config generation (op25_client.generate_config) rewrites the device to
  rtl=<serial>: the pin, else the first dongle's serial, which is what
  "rtl" always opened. Left as "rtl" only for unknown/shared serials.
- secondary-sdr: /secondary/devices lists dongles + serials via librtlsdr
  (works while claimed). apply(priority, pins, reserved) never touches
  OP25's dongle, gives a pinned service only its own dongle, lets a
  higher-priority service take a spare from a lower one, and still runs a
  pinned lower-priority service when the top pick has no dongle.
- sdr_settings.py replaces secondary_priority.py: one apply path for the
  local dashboard, the new set_sdr_config C2 command (set_secondary_priority
  kept as an alias) and config pushes. OP25 restarts only when its own
  dongle changes. Checkin reports sdr_devices, sdr_pins, op25_sdr_serial.
- Local dashboard: 'SDRs' card with an OP25 SDR dropdown and a per-service
  dongle dropdown, duplicate-serial and double-pin warnings.

Verified: edge-node pytest 194 passed; secondary-sdr tests 7 passed;
flake8 clean; page JS passes node --check.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/build-secondary-sdr.yml

@@ -0,0 +1,52 @@
+name: Build secondary-sdr
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [main, master]
+    paths:
+      - "secondary-sdr-container/**"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    env:
+      CONTAINER_NAME: secondary-sdr
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-qemu-action@v3
+
+      - uses: docker/setup-buildx-action@v3
+        with:
+          config-inline: |
+            [registry."git.vpn.cusano.net"]
+              http = false
+              insecure = false
+
+      - uses: docker/login-action@v3
+        with:
+          registry: git.vpn.cusano.net
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.BUILD_TOKEN }}
+
+      - name: Get version
+        id: meta
+        run: |
+          echo "REPO_NAME=$(echo ${GITHUB_REPOSITORY} | awk -F'/' '{print $2}')" >> $GITHUB_OUTPUT
+          echo "VERSION=$(git describe --tags --always | sed 's/^v//')" >> $GITHUB_OUTPUT
+
+      - uses: docker/build-push-action@v6
+        with:
+          context: ./secondary-sdr-container
+          file: ./secondary-sdr-container/Dockerfile
+          platforms: linux/arm64
+          push: true
+          tags: |
+            git.vpn.cusano.net/${{ vars.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}/${{ env.CONTAINER_NAME }}:${{ steps.meta.outputs.VERSION }}
+            git.vpn.cusano.net/${{ vars.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}/${{ env.CONTAINER_NAME }}:latest
+          cache-from: type=registry,ref=git.vpn.cusano.net/${{ vars.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}/${{ env.CONTAINER_NAME }}:buildcache
+          cache-to: type=registry,ref=git.vpn.cusano.net/${{ vars.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}/${{ env.CONTAINER_NAME }}:buildcache,mode=max

drb-edge-node/app/internal/mqtt_manager.py

@@ -210,10 +210,14 @@ class MQTTManager:
             logger.info("No API key on disk — requesting re-delivery from C2 server.")
             self._publish(self._t_key_request, {}, qos=1)
 
+    async def publish_checkin(self):
+        await self._publish_checkin()
+
     async def _publish_checkin(self):
         from app.internal.discord_radio import radio_bot
         from app.internal.config_manager import load_node_config
         from app.internal.op25_client import op25_client
+        from app.internal.secondary_sdr_client import secondary_sdr_client
         config = load_node_config()
         devices = await op25_client.devices()
         payload = {
@@ -228,11 +232,28 @@ class MQTTManager:
             "override_system_id": config.override_system_id,
             "enforce_override_timeout": config.enforce_override_timeout,
             "secondary_sdr_mode": config.secondary_sdr_mode,
+            "secondary_sdr_priority": config.secondary_sdr_priority,
         }
-        # Best-effort — the first node-initiated hardware-report field. Omit
-        # rather than guess if op25's control API is unreachable.
-        if devices is not None:
-            payload["sdr_count"] = devices.get("count")
+        payload["sdr_pins"] = config.sdr_pins
+        secondary = await secondary_sdr_client.status()
+        if secondary is not None:
+            payload["secondary_sdr_running"] = [r["mode"] for r in secondary.get("running", [])]
+            if secondary.get("devices") is not None:
+                payload["sdr_devices"] = [
+                    {k: d.get(k) for k in ("index", "serial", "name", "duplicate_serial")}
+                    for d in secondary["devices"]
+                ]
+                from app.internal.sdr_settings import op25_serial
+                payload["op25_sdr_serial"] = op25_serial(config, secondary["devices"])
+        # Best-effort hardware report — omit rather than guess. Prefer the
+        # secondary-sdr container's count: op25's :stable image has no lsusb and
+        # its /op25/devices answers 0 rather than "unknown" when that fails. A
+        # node running op25 has at least one SDR, so 0 is never a real reading.
+        count = secondary.get("sdr_count") if secondary is not None else None
+        if not count and devices:
+            count = devices.get("count") or None
+        if count is not None:
+            payload["sdr_count"] = count
         self._publish(self._t_checkin, payload, qos=1)
 
     def _publish(self, topic: str, payload: dict, qos: int = 0, retain: bool = False):

drb-edge-node/app/internal/op25_client.py

@@ -80,10 +80,14 @@ class OP25Client:
             async with httpx.AsyncClient(timeout=10) as client:
                 r = await client.post(f"{self.api_url}/op25/generate-config", json=config)
                 r.raise_for_status()
-                return True
         except Exception as e:
             logger.error(f"OP25 generate-config failed: {e}")
             return False
+        # Every generated config opens its dongle by serial, never "first
+        # found" (node-26#11) — here so no generation path can skip it.
+        from app.internal.sdr_settings import pin_op25_device
+        await pin_op25_device()
+        return True
 
     async def poll_terminal(self) -> Optional[TerminalUpdate]:
         """

drb-edge-node/app/internal/sdr_settings.py

@@ -0,0 +1,102 @@
+"""
+Which SDR does what on this node (node-26#9, node-26#11).
+
+- OP25 always has exactly one dongle. `sdr_pins["op25"]` names it by serial;
+  unpinned, OP25 keeps its historical "first dongle" — but that dongle is now
+  named by serial too, so the decoders can never take it out from under OP25.
+- Every other dongle runs the next enabled service in `secondary_sdr_priority`.
+  `sdr_pins[mode]` optionally binds a service to the dongle carrying its
+  antenna; unpinned services take any spare.
+
+One apply path for the local dashboard, C2 commands and config pushes.
+"""
+import asyncio
+import json
+from pathlib import Path
+from typing import Any, Dict, Iterable, List, Optional
+
+from app.config import settings
+from app.internal.config_manager import load_node_config, save_node_config
+from app.internal.logger import logger
+from app.internal.secondary_sdr_client import secondary_sdr_client
+from app.models import NodeConfig, normalize_sdr_pins, normalize_secondary_priority
+
+_OP25_CONFIG = Path(settings.config_path) / "active.cfg.json"
+
+
+def op25_serial(cfg: NodeConfig, devs: Optional[List[Dict[str, Any]]]) -> Optional[str]:
+    """The serial of OP25's dongle: the pin, else the first detected dongle
+    (what OP25's plain "rtl" device string has always opened)."""
+    if cfg.sdr_pins.get("op25"):
+        return cfg.sdr_pins["op25"]
+    return devs[0]["serial"] if devs else None
+
+
+async def pin_op25_device() -> Optional[str]:
+    """Rewrite OP25's generated config to open its dongle by serial.
+
+    Runs after every generate-config (op25_client.generate_config). A plain
+    "rtl" means "device 0", and which dongle is device 0 depends on who opened
+    what first — that is how OP25 lost its SDR to readsb on 2026-09-27.
+    Left as "rtl" only when the serial is unknown or shared by two dongles.
+    """
+    devs = await secondary_sdr_client.devices()
+    serial = op25_serial(load_node_config(), devs)
+    if not serial or (devs and sum(d["serial"] == serial for d in devs) > 1):
+        return None
+    try:
+        cfg = json.loads(_OP25_CONFIG.read_text())
+        for dev in cfg.get("devices", []):
+            dev["args"] = f"rtl={serial}"
+        _OP25_CONFIG.write_text(json.dumps(cfg, indent=2))
+    except Exception as e:
+        logger.error(f"Could not pin OP25 to SDR {serial}: {e}")
+        return None
+    return serial
+
+
+async def apply_secondaries() -> Optional[List[str]]:
+    """Start/stop decoders to match the saved priority and pins, never on OP25's dongle."""
+    cfg = load_node_config()
+    if not cfg.secondary_sdr_priority:
+        return await secondary_sdr_client.apply([], {}, [])
+    devs = await secondary_sdr_client.devices()
+    reserved = [s for s in [op25_serial(cfg, devs)] if s]
+    pins = {m: s for m, s in cfg.sdr_pins.items() if m != "op25"}
+    return await secondary_sdr_client.apply(cfg.secondary_sdr_priority, pins, reserved)
+
+
+async def set_sdr_settings(priority: Optional[Iterable[str]] = None,
+                           pins: Optional[Dict[str, Optional[str]]] = None) -> Optional[List[str]]:
+    """Persist and apply priority and/or pins. OP25 restarts only if its own
+    dongle changed; reordering the spare dongles never interrupts P25.
+
+    Returns the decoders now running (None if the container is unreachable).
+    """
+    cfg = load_node_config()
+    old_op25 = cfg.sdr_pins.get("op25")
+    if priority is not None:
+        ordered = normalize_secondary_priority(priority)
+        cfg.secondary_sdr_priority = ordered
+        cfg.secondary_sdr_mode = ordered[0] if ordered else "none"
+    if pins is not None:
+        cfg.sdr_pins = normalize_sdr_pins(pins)
+    save_node_config(cfg)
+
+    if cfg.sdr_pins.get("op25") != old_op25:
+        from app.internal.op25_client import op25_client
+        # Free the new dongle first if a decoder holds it, then move OP25.
+        await secondary_sdr_client.apply([], {}, [])
+        serial = await pin_op25_device()
+        await op25_client.stop()
+        await asyncio.sleep(2)
+        await op25_client.start()
+        logger.info(f"OP25 moved to SDR {serial or 'rtl (first dongle)'}")
+
+    running = await apply_secondaries()
+    logger.info(f"SDR settings: priority={cfg.secondary_sdr_priority!r} pins={cfg.sdr_pins!r}; running {running!r}")
+
+    # Report straight away so C2's view doesn't wait for the next heartbeat.
+    from app.internal.mqtt_manager import mqtt_manager
+    asyncio.create_task(mqtt_manager.publish_checkin())
+    return running

drb-edge-node/app/internal/secondary_sdr_client.py

@@ -1,5 +1,5 @@
 import httpx
-from typing import Any, Dict, Optional
+from typing import Any, Dict, List, Optional
 from app.config import settings
 from app.internal.logger import logger
 
@@ -15,6 +15,31 @@ class SecondarySdrClient:
     def __init__(self):
         self.api_url = settings.secondary_sdr_api_url
 
+    async def devices(self) -> Optional[List[Dict[str, Any]]]:
+        """Every RTL-SDR on the node with its serial, or None if unreachable."""
+        try:
+            async with httpx.AsyncClient(timeout=5) as client:
+                r = await client.get(f"{self.api_url}/secondary/devices")
+                r.raise_for_status()
+                return r.json().get("devices", [])
+        except Exception as e:
+            logger.error(f"Secondary SDR device list failed: {e}")
+            return None
+
+    async def apply(self, priority: List[str], pins: Dict[str, str], reserved: List[str]) -> Optional[List[str]]:
+        """Run decoders down the priority list until SDRs run out, honouring
+        pins and never touching `reserved` (op25's) dongles. Returns the modes
+        actually running, or None if the container is unreachable."""
+        body = {"priority": priority, "pins": pins, "reserved": reserved}
+        try:
+            async with httpx.AsyncClient(timeout=30) as client:
+                r = await client.post(f"{self.api_url}/secondary/apply", json=body)
+                r.raise_for_status()
+                return r.json().get("running", [])
+        except Exception as e:
+            logger.error(f"Secondary SDR apply (priority={priority!r}) failed: {e}")
+            return None
+
     async def start(self, mode: str) -> bool:
         try:
             async with httpx.AsyncClient(timeout=10) as client:

drb-edge-node/app/internal/telemetry_uplink.py

@@ -32,13 +32,14 @@ async def _post_snapshot(path: str, body: dict) -> None:
 async def telemetry_uplink_loop():
     while True:
         await asyncio.sleep(UPLINK_INTERVAL_SECONDS)
-        config = load_node_config()
-        if config.secondary_sdr_mode not in ("adsb", "ais"):
+        if not load_node_config().secondary_sdr_priority:
             continue
         snapshot = await secondary_sdr_client.data()
         if not snapshot:
             continue
-        if config.secondary_sdr_mode == "adsb" and snapshot.get("aircraft"):
+        # Several decoders can run at once (one per spare SDR), so forward
+        # whatever each produced rather than keying off a single mode.
+        if snapshot.get("aircraft"):
             await _post_snapshot("/telemetry/adsb", {"aircraft": snapshot["aircraft"]})
-        elif config.secondary_sdr_mode == "ais" and snapshot.get("vessels"):
+        if snapshot.get("vessels"):
             await _post_snapshot("/telemetry/ais", {"vessels": snapshot["vessels"]})

drb-edge-node/app/main.py

@@ -5,7 +5,7 @@ from typing import Optional
 
 from fastapi import FastAPI
 from app.config import settings
-from app.models import SystemConfig
+from app.models import SystemConfig, normalize_sdr_pins, normalize_secondary_priority
 from app.internal.logger import logger
 from app.internal.mqtt_manager import mqtt_manager
 from app.internal import credentials
@@ -158,6 +158,12 @@ async def on_command(payload: dict):
         )
     elif action == "discord_leave":
         await radio_bot.leave()
+    elif action in ("set_sdr_config", "set_secondary_priority"):
+        from app.internal.sdr_settings import set_sdr_settings
+        try:
+            await set_sdr_settings(payload.get("priority"), payload.get("pins"))
+        except ValueError as e:
+            logger.error(f"Rejected SDR settings from C2: {e}")
     elif action == "op25_restart":
         from app.internal.op25_client import op25_client
         await op25_client.stop()
@@ -224,7 +230,9 @@ async def on_config_push(payload: dict):
     hardware_preset = payload.pop("hardware_preset", None)
     ppm_override = payload.pop("ppm_override", None)
     node_type = payload.pop("node_type", None)
-    secondary_sdr_mode = payload.pop("secondary_sdr_mode", None)
+    secondary_sdr_priority = payload.pop("secondary_sdr_priority", None)
+    sdr_pins = payload.pop("sdr_pins", None)
+    secondary_sdr_mode = payload.pop("secondary_sdr_mode", None)  # legacy single-mode C2
     enforce_override_timeout = payload.pop("enforce_override_timeout", None)
     try:
         config = SystemConfig(**payload)
@@ -244,10 +252,18 @@ async def on_config_push(payload: dict):
         node_cfg.ppm_override = float(ppm_override)
     if node_type is not None:
         node_cfg.node_type = node_type
-    if secondary_sdr_mode is not None:
-        node_cfg.secondary_sdr_mode = secondary_sdr_mode
     if enforce_override_timeout is not None:
         node_cfg.enforce_override_timeout = bool(enforce_override_timeout)
+    if secondary_sdr_priority is None and secondary_sdr_mode is not None:
+        secondary_sdr_priority = [secondary_sdr_mode]
+    if secondary_sdr_priority is not None:
+        node_cfg.secondary_sdr_priority = normalize_secondary_priority(secondary_sdr_priority)
+        node_cfg.secondary_sdr_mode = (node_cfg.secondary_sdr_priority or ["none"])[0]
+    if sdr_pins is not None:
+        try:
+            node_cfg.sdr_pins = normalize_sdr_pins(sdr_pins)
+        except ValueError as e:
+            logger.error(f"Ignoring invalid sdr_pins in config push: {e}")
     save_node_config(node_cfg)
 
     from app.internal.op25_client import op25_client
@@ -255,17 +271,16 @@ async def on_config_push(payload: dict):
         logger.error(f"Failed to generate OP25 config for {config.name}")
         return
 
+    # OP25's (pinned) dongle may be one a decoder holds right now: free the
+    # spares, restart OP25 on its own dongle, then hand the rest back out.
+    from app.internal.secondary_sdr_client import secondary_sdr_client
+    from app.internal.sdr_settings import apply_secondaries
+    await secondary_sdr_client.apply([], {}, [])
     await op25_client.stop()
     await asyncio.sleep(2)
     await op25_client.start()
     logger.info(f"Config push applied: {config.name}")
-
-    if secondary_sdr_mode is not None:
-        from app.internal.secondary_sdr_client import secondary_sdr_client
-        if secondary_sdr_mode in ("adsb", "ais"):
-            await secondary_sdr_client.start(secondary_sdr_mode)
-        else:
-            await secondary_sdr_client.stop()
+    await apply_secondaries()
 
 
 # ---------------------------------------------------------------------------
@@ -322,10 +337,11 @@ async def lifespan(app: FastAPI):
             logger.warning(f"OP25 not ready yet (attempt {attempt + 1}/10), retrying in 3s…")
             await asyncio.sleep(3)
 
-    if node_cfg.secondary_sdr_mode in ("adsb", "ais"):
-        from app.internal.secondary_sdr_client import secondary_sdr_client
-        logger.info(f"Resuming secondary SDR (mode={node_cfg.secondary_sdr_mode!r}) after restart.")
-        await secondary_sdr_client.start(node_cfg.secondary_sdr_mode)
+    # After op25 has claimed its dongle, so the decoders only get the spares.
+    if node_cfg.secondary_sdr_priority:
+        from app.internal.sdr_settings import apply_secondaries
+        logger.info(f"Resuming secondary SDRs (priority={node_cfg.secondary_sdr_priority!r}) after restart.")
+        await apply_secondaries()
 
     heartbeat_task = asyncio.create_task(mqtt_manager.heartbeat_loop())
     from app.internal.telemetry_uplink import telemetry_uplink_loop

drb-edge-node/app/models.py

@@ -1,5 +1,5 @@
-from pydantic import BaseModel
-from typing import Optional, Dict, Any
+from pydantic import BaseModel, model_validator
+from typing import Optional, Dict, Any, Iterable, List
 from enum import Enum
 from datetime import datetime
 
@@ -23,6 +23,34 @@ class SystemConfig(BaseModel):
     config: Dict[str, Any]  # OP25-compatible config blob passed through to op25-container
 
 
+# Decoders a node can run on the SDRs beyond op25's (node-26#9). op25 always
+# keeps its own dongle; each further dongle runs the next entry of the node's
+# secondary_sdr_priority, so a 3-SDR node with ["adsb", "ais"] runs both.
+SECONDARY_SDR_MODES = ("adsb", "ais")
+
+
+def normalize_secondary_priority(items: Iterable[str]) -> List[str]:
+    """Known modes only, first occurrence wins, order preserved."""
+    out: List[str] = []
+    for m in items or []:
+        if m in SECONDARY_SDR_MODES and m not in out:
+            out.append(m)
+    return out
+
+
+# Services that can be bound to a specific dongle by its USB serial.
+SDR_PIN_KEYS = ("op25",) + SECONDARY_SDR_MODES
+
+
+def normalize_sdr_pins(pins: Dict[str, Optional[str]]) -> Dict[str, str]:
+    """Known services only, blank = automatic (dropped). Two services can't
+    share a dongle, so a serial claimed twice raises."""
+    out = {k: str(v).strip() for k, v in (pins or {}).items() if k in SDR_PIN_KEYS and v and str(v).strip()}
+    if len(set(out.values())) != len(out):
+        raise ValueError("Two services can't be pinned to the same SDR.")
+    return out
+
+
 class NodeConfig(BaseModel):
     node_id: str
     node_name: str
@@ -34,12 +62,23 @@ class NodeConfig(BaseModel):
     hardware_preset: str = "rtl-sdr-v3"
     ppm_override: Optional[float] = None
     node_type: str = "fixed"  # fixed or portable
-    secondary_sdr_mode: str = "none"  # none | adsb | ais | op25_2 — requires a second physical SDR
+    secondary_sdr_priority: List[str] = []  # ordered; SDRs beyond op25's run these top-down
+    sdr_pins: Dict[str, str] = {}  # service (op25/adsb/ais) -> dongle serial; absent = automatic
+    # Legacy single-mode field (pre-priority). Still written as priority[0] so
+    # an older C2 reading checkins sees something sensible; read only to
+    # migrate a node_config.json saved before priority existed.
+    secondary_sdr_mode: str = "none"
     enforce_override_timeout: bool = True
     override_system_id: Optional[str] = None
     override_config: Optional[SystemConfig] = None
     offline_call_buffer_size: int = 35  # max call_end events to buffer while MQTT is offline
 
+    @model_validator(mode="after")
+    def _migrate_secondary_mode(self) -> "NodeConfig":
+        if not self.secondary_sdr_priority and self.secondary_sdr_mode in SECONDARY_SDR_MODES:
+            self.secondary_sdr_priority = [self.secondary_sdr_mode]
+        return self
+
 
 class CallEvent(BaseModel):
     call_id: str

drb-edge-node/app/routers/api.py

@@ -1,9 +1,10 @@
 from fastapi import APIRouter, Depends, HTTPException, Body
-from typing import Optional
+from pydantic import BaseModel
+from typing import Dict, List, Optional
 import asyncio
 import httpx
 from app.config import settings
-from app.models import SystemConfig
+from app.models import SystemConfig, SECONDARY_SDR_MODES
 from app.internal.op25_client import op25_client
 from app.internal.config_manager import load_node_config, save_node_config, apply_system_config
 from app.internal.call_recorder import call_recorder
@@ -204,6 +205,44 @@ async def ack_override(timeout_minutes: int = Body(1440)):
         raise HTTPException(500, f"Failed to contact C2: {e}")
 
 
+@router.get("/sdr")
+async def get_sdr():
+    """Which SDR does what: detected dongles, pins, priority, what's running."""
+    from app.internal.secondary_sdr_client import secondary_sdr_client
+    from app.internal.sdr_settings import op25_serial
+    cfg = load_node_config()
+    devs = await secondary_sdr_client.devices()
+    status = await secondary_sdr_client.status()
+    return {
+        "devices": devs,  # None = secondary-sdr service unreachable
+        "op25_serial": op25_serial(cfg, devs),
+        "pins": cfg.sdr_pins,
+        "priority": cfg.secondary_sdr_priority,
+        "modes": list(SECONDARY_SDR_MODES),
+        "running": [r["mode"] for r in status.get("running", [])] if status else None,
+    }
+
+
+class SdrSettingsBody(BaseModel):
+    priority: Optional[List[str]] = None
+    pins: Optional[Dict[str, Optional[str]]] = None  # service -> serial; null/"" = automatic
+
+
+@router.post("/sdr")
+async def set_sdr(body: SdrSettingsBody):
+    """Set priority and/or pins. Restarts OP25 only if OP25's own SDR changes."""
+    from app.internal.sdr_settings import set_sdr_settings
+    if body.priority is not None:
+        unknown = [m for m in body.priority if m not in SECONDARY_SDR_MODES]
+        if unknown:
+            raise HTTPException(400, f"Unknown secondary SDR mode(s): {unknown}")
+    try:
+        running = await set_sdr_settings(body.priority, body.pins)
+    except ValueError as e:
+        raise HTTPException(400, str(e))
+    return {"ok": True, "running": running}
+
+
 @router.post("/discord/join")
 async def discord_join(guild_id: int, channel_id: int):
     ok = await radio_bot.join(guild_id, channel_id)

drb-edge-node/app/templates/index.html

@@ -105,6 +105,40 @@
       background: rgba(255, 255, 255, 0.1);
     }
 
+    .sdr-row {
+      display: flex;
+      align-items: center;
+      gap: 0.6rem;
+      padding: 0.55rem 0;
+      border-bottom: 1px solid var(--glass-border);
+    }
+    .sdr-row:last-child { border-bottom: none; }
+    .sdr-rank { width: 1.2rem; color: var(--text-muted); font-size: 0.8rem; text-align: right; }
+    .sdr-name { flex: 1; }
+    .sdr-name small { display: block; color: var(--text-muted); font-size: 0.75rem; }
+    .sdr-move {
+      background: rgba(255, 255, 255, 0.05);
+      border: 1px solid var(--glass-border);
+      color: var(--text-main);
+      border-radius: 6px;
+      width: 1.9rem;
+      height: 1.9rem;
+      cursor: pointer;
+    }
+    .sdr-move:disabled { opacity: 0.3; cursor: default; }
+    .sdr-state { font-size: 0.75rem; min-width: 6.5rem; text-align: right; color: var(--text-muted); }
+    .sdr-state.on { color: var(--success); }
+    .sdr-select {
+      background: rgba(255, 255, 255, 0.05);
+      border: 1px solid var(--glass-border);
+      color: var(--text-main);
+      border-radius: 6px;
+      padding: 0.3rem 0.4rem;
+      font-size: 0.8rem;
+      max-width: 13rem;
+    }
+    .sdr-select option { background: #111827; }
+
     .grid {
       display: grid;
       grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
@@ -360,6 +394,28 @@
         </div>
       </div>
 
+      <!-- SDRs Card (node-26#9, #11) -->
+      <div class="glass-card">
+        <div class="card-header">
+          <div class="card-title">SDRs</div>
+        </div>
+        <div class="data-row" style="align-items:center;">
+          <span class="data-label">OP25 SDR</span>
+          <select id="sdr-op25" class="sdr-select" aria-label="OP25 SDR"></select>
+        </div>
+        <p id="sdr-op25-note" style="color: var(--text-muted); font-size: 0.75rem; margin: 0.25rem 0 0.75rem;"></p>
+        <p style="color: var(--text-muted); font-size: 0.8rem; margin: 0 0 0.5rem;">
+          Every other SDR runs the next enabled service, top first. Pin a service to the SDR
+          that has its antenna, or leave it on "Any spare SDR".
+        </p>
+        <div id="sdr-list"></div>
+        <p id="sdr-warning" style="color: var(--danger); font-size: 0.8rem; margin: 0.5rem 0 0; display:none;"></p>
+        <div style="display:flex; gap:0.75rem; align-items:center; margin-top:0.75rem;">
+          <button id="sdr-save" class="btn btn-primary" style="padding:0.5rem 1rem;" onclick="saveSdr()" disabled>Save</button>
+          <span id="sdr-msg" style="color: var(--text-muted); font-size: 0.8rem;"></span>
+        </div>
+      </div>
+
       <!-- Local Listening Card -->
       <div class="glass-card player-card">
         <div class="card-header" style="margin-bottom:0.5rem; border:none;">
@@ -492,6 +548,133 @@
       }
     }
 
+    // ── SDRs: OP25's dongle, secondary priority and per-service pins ────────
+    const SDR_LABELS = {
+      adsb: ['ADS-B', 'Aircraft · 1090 MHz'],
+      ais: ['AIS', 'Vessels · 162 MHz'],
+    };
+    let sdr = null;         // last GET /api/sdr
+    let sdrRows = [];       // [{mode, enabled, pin}] in display order
+    let sdrOp25Pin = '';    // '' = automatic
+    let sdrDirty = false;
+
+    function esc(v) {
+      return String(v ?? '').replace(/[&<>"']/g, c => ({'&': '&amp;', '<': '&lt;', '>': '&gt;', '"': '&quot;', "'": '&#39;'}[c]));
+    }
+
+    function deviceOptions(selected, autoLabel) {
+      const devs = sdr.devices || [];
+      const known = devs.some(d => d.serial === selected);
+      return `<option value="">${esc(autoLabel)}</option>` +
+        devs.map(d => `<option value="${esc(d.serial)}" ${d.serial === selected ? 'selected' : ''}>` +
+          `SDR ${d.index + 1} · serial ${esc(d.serial)}${d.duplicate_serial ? ' (shared serial!)' : ''}</option>`).join('') +
+        (selected && !known ? `<option value="${esc(selected)}" selected>serial ${esc(selected)} (not plugged in)</option>` : '');
+    }
+
+    function renderSdr() {
+      const op25 = document.getElementById('sdr-op25');
+      op25.innerHTML = deviceOptions(sdrOp25Pin, 'Automatic (first SDR)');
+      op25.onchange = () => { sdrOp25Pin = op25.value; markSdrDirty(); };
+      document.getElementById('sdr-op25-note').textContent = sdrOp25Pin !== (sdr.pins.op25 || '')
+        ? 'Saving will restart OP25 on the selected SDR.'
+        : (sdr.op25_serial ? `OP25 is using serial ${sdr.op25_serial}.` : '');
+
+      const list = document.getElementById('sdr-list');
+      list.innerHTML = '';
+      let rank = 0;
+      const running = sdr.running || [];
+      sdrRows.forEach((row, i) => {
+        const [name, hint] = SDR_LABELS[row.mode] || [row.mode, ''];
+        const pinMissing = row.pin && !(sdr.devices || []).some(d => d.serial === row.pin);
+        const state = !row.enabled ? 'Off'
+          : sdrDirty ? 'Unsaved'
+          : sdr.running === null ? 'Unknown'
+          : running.includes(row.mode) ? 'Running'
+          : pinMissing ? 'Pinned SDR missing' : 'Waiting for SDR';
+        const el = document.createElement('div');
+        el.className = 'sdr-row';
+        el.innerHTML = `
+          <span class="sdr-rank">${row.enabled ? ++rank : ''}</span>
+          <input type="checkbox" ${row.enabled ? 'checked' : ''} aria-label="Enable ${name}">
+          <span class="sdr-name">${name}<small>${hint}</small></span>
+          <select class="sdr-select" aria-label="${name} SDR">${deviceOptions(row.pin, 'Any spare SDR')}</select>
+          <button class="sdr-move" aria-label="Move ${name} up" ${i === 0 ? 'disabled' : ''}>▲</button>
+          <button class="sdr-move" aria-label="Move ${name} down" ${i === sdrRows.length - 1 ? 'disabled' : ''}>▼</button>
+          <span class="sdr-state ${state === 'Running' ? 'on' : ''}">${state}</span>`;
+        const [box] = el.getElementsByTagName('input');
+        const [pick] = el.getElementsByTagName('select');
+        const [up, down] = el.getElementsByTagName('button');
+        box.onchange = () => { row.enabled = box.checked; markSdrDirty(); };
+        pick.onchange = () => { row.pin = pick.value; markSdrDirty(); };
+        up.onclick = () => { [sdrRows[i - 1], sdrRows[i]] = [sdrRows[i], sdrRows[i - 1]]; markSdrDirty(); };
+        down.onclick = () => { [sdrRows[i + 1], sdrRows[i]] = [sdrRows[i], sdrRows[i + 1]]; markSdrDirty(); };
+        list.appendChild(el);
+      });
+
+      const warn = document.getElementById('sdr-warning');
+      const pinned = [sdrOp25Pin, ...sdrRows.map(r => r.pin)].filter(Boolean);
+      const problems = [];
+      if (sdr.devices === null) problems.push('The secondary SDR service is not responding, so SDRs can\'t be listed.');
+      if ((sdr.devices || []).some(d => d.duplicate_serial)) {
+        problems.push('Two SDRs share a serial number, so they can\'t be told apart. Give each a unique serial (rtl_eeprom -s) before pinning.');
+      }
+      if (new Set(pinned).size !== pinned.length) problems.push('Two services are pinned to the same SDR.');
+      warn.textContent = problems.join(' ');
+      warn.style.display = problems.length ? 'block' : 'none';
+      document.getElementById('sdr-save').disabled = !sdrDirty || new Set(pinned).size !== pinned.length;
+    }
+
+    function markSdrDirty() {
+      sdrDirty = true;
+      document.getElementById('sdr-msg').textContent = '';
+      renderSdr();
+    }
+
+    async function loadSdr() {
+      if (sdrDirty) return;  // never clobber unsaved edits with a poll
+      try {
+        const r = await fetch('/api/sdr');
+        if (!r.ok) return;
+        sdr = await r.json();
+        sdrOp25Pin = sdr.pins.op25 || '';
+        sdrRows = [
+          ...sdr.priority.map(mode => ({ mode, enabled: true, pin: sdr.pins[mode] || '' })),
+          ...sdr.modes.filter(m => !sdr.priority.includes(m)).map(mode => ({ mode, enabled: false, pin: sdr.pins[mode] || '' })),
+        ];
+        renderSdr();
+      } catch (e) {
+        console.error('SDR load failed:', e);
+      }
+    }
+
+    async function saveSdr() {
+      const pins = { op25: sdrOp25Pin || null };
+      sdrRows.forEach(r => { pins[r.mode] = r.pin || null; });
+      const btn = document.getElementById('sdr-save');
+      const msg = document.getElementById('sdr-msg');
+      btn.disabled = true;
+      msg.textContent = 'Applying…';
+      try {
+        const r = await fetch('/api/sdr', {
+          method: 'POST',
+          headers: { 'Content-Type': 'application/json' },
+          body: JSON.stringify({ priority: sdrRows.filter(r => r.enabled).map(r => r.mode), pins }),
+        });
+        if (!r.ok) throw new Error((await r.json().catch(() => ({}))).detail || r.statusText);
+        const d = await r.json();
+        sdrDirty = false;
+        msg.textContent = d.running === null ? 'Saved, but the secondary SDR service did not respond.' : 'Saved.';
+        await loadSdr();
+      } catch (e) {
+        console.error('SDR save failed:', e);
+        msg.textContent = `Save failed: ${e.message}`;
+        btn.disabled = false;
+      }
+    }
+
+    loadSdr();
+    setInterval(loadSdr, 10000);
+
     refresh();
     setInterval(refresh, 2000); // Polling every 2 seconds
   </script>

drb-edge-node/tests/test_sdr_settings.py

@@ -0,0 +1,91 @@
+"""
+node-26#9 / #11 — which SDR does what: secondary priority, per-service pins,
+and OP25 always opening its dongle by serial.
+"""
+import asyncio
+import json
+from unittest.mock import AsyncMock, patch
+
+import pytest
+
+from app.models import NodeConfig, normalize_sdr_pins, normalize_secondary_priority
+
+DEVS = [
+    {"index": 0, "serial": "69420", "name": "RTL", "duplicate_serial": False},
+    {"index": 1, "serial": "00000001", "name": "RTL", "duplicate_serial": False},
+]
+
+
+def _cfg(**kw) -> NodeConfig:
+    return NodeConfig(node_id="n1", node_name="N1", lat=0.0, lon=0.0, **kw)
+
+
+def test_normalize_priority_keeps_order_drops_unknown_and_duplicates():
+    assert normalize_secondary_priority(["ais", "bogus", "adsb", "ais"]) == ["ais", "adsb"]
+
+
+def test_legacy_single_mode_migrates_to_priority():
+    assert _cfg(secondary_sdr_mode="adsb").secondary_sdr_priority == ["adsb"]
+    assert _cfg(secondary_sdr_mode="adsb", secondary_sdr_priority=["ais"]).secondary_sdr_priority == ["ais"]
+
+
+def test_pins_drop_blanks_and_unknown_services():
+    assert normalize_sdr_pins({"op25": "00000001", "adsb": "", "ais": None, "x": "1"}) == {"op25": "00000001"}
+
+
+def test_two_services_cannot_share_a_dongle():
+    with pytest.raises(ValueError):
+        normalize_sdr_pins({"op25": "69420", "adsb": "69420"})
+
+
+@pytest.fixture
+def node(tmp_path):
+    """Isolated node_config.json + OP25 active.cfg.json, mocked decoders/op25/mqtt."""
+    import app.internal.config_manager as cm
+    from app.internal import sdr_settings as ss
+    op25_cfg = tmp_path / "active.cfg.json"
+    op25_cfg.write_text(json.dumps({"devices": [{"args": "rtl", "name": "sdr"}]}))
+    with patch.object(cm, "_CONFIG_FILE", tmp_path / "node_config.json"), \
+         patch.object(ss, "_OP25_CONFIG", op25_cfg), \
+         patch.object(ss.secondary_sdr_client, "devices", AsyncMock(return_value=DEVS)), \
+         patch.object(ss.secondary_sdr_client, "apply", AsyncMock(return_value=["adsb"])) as apply, \
+         patch("app.internal.op25_client.op25_client.stop", AsyncMock()) as op25_stop, \
+         patch("app.internal.op25_client.op25_client.start", AsyncMock()), \
+         patch("app.internal.mqtt_manager.mqtt_manager.publish_checkin", AsyncMock()), \
+         patch("asyncio.sleep", AsyncMock()):
+        cm.save_node_config(_cfg())
+        yield {"cm": cm, "ss": ss, "apply": apply, "op25_stop": op25_stop,
+               "op25_args": lambda: json.loads(op25_cfg.read_text())["devices"][0]["args"]}
+
+
+def test_unpinned_op25_is_still_opened_by_serial_of_the_first_dongle(node):
+    assert asyncio.run(node["ss"].pin_op25_device()) == "69420"
+    assert node["op25_args"]() == "rtl=69420"
+
+
+def test_pinned_op25_opens_its_pinned_dongle(node):
+    node["cm"].save_node_config(_cfg(sdr_pins={"op25": "00000001"}))
+    asyncio.run(node["ss"].pin_op25_device())
+    assert node["op25_args"]() == "rtl=00000001"
+
+
+def test_shared_serial_leaves_op25_on_plain_rtl(node):
+    dup = [dict(d, serial="00000001") for d in DEVS]
+    with patch.object(node["ss"].secondary_sdr_client, "devices", AsyncMock(return_value=dup)):
+        assert asyncio.run(node["ss"].pin_op25_device()) is None
+    assert node["op25_args"]() == "rtl"
+
+
+def test_priority_change_never_restarts_op25_and_reserves_its_dongle(node):
+    node["cm"].save_node_config(_cfg(sdr_pins={"op25": "00000001"}))
+    asyncio.run(node["ss"].set_sdr_settings(priority=["adsb", "ais"]))
+    node["op25_stop"].assert_not_awaited()
+    node["apply"].assert_awaited_with(["adsb", "ais"], {}, ["00000001"])
+
+
+def test_moving_op25_restarts_it_on_the_new_dongle(node):
+    asyncio.run(node["ss"].set_sdr_settings(priority=["adsb"], pins={"op25": "00000001", "adsb": "69420"}))
+    node["op25_stop"].assert_awaited_once()
+    assert node["op25_args"]() == "rtl=00000001"
+    node["apply"].assert_awaited_with(["adsb"], {"adsb": "69420"}, ["00000001"])
+    assert node["cm"].load_node_config().sdr_pins == {"op25": "00000001", "adsb": "69420"}

secondary-sdr-container/app/internal/decoder_control.py

@@ -1,3 +1,5 @@
+import ctypes
+import ctypes.util
 import json
 import os
 import signal
@@ -10,64 +12,59 @@ from internal.logger import create_logger
 
 LOGGER = create_logger(__name__)
 
-# AIS-catcher streams one JSON object per received message on stdout rather
-# than writing a periodic snapshot file (dump1090's approach above) — so the
-# current-vessel snapshot lives in memory, keyed by mmsi, kept warm by a
-# background reader thread for as long as the subprocess we started is
-# alive. Unlike the pgid-file state, this does NOT survive this API
-# process restarting independently of its subprocess — acceptable since
-# nothing here does that today.
-_ais_vessels: Dict[str, Dict[str, Any]] = {}
-_ais_lock = threading.Lock()
+# One decoder per mode, each on its own SDR (node-26#9). The node's secondary
+# SDR *priority* (e.g. ["adsb", "ais"]) is applied by apply(): decoders start
+# down the list until no free dongle is left, so every SDR the node has gets
+# used and the ones beyond the list's reach simply aren't started. OP25 always
+# keeps its own dongle — it is started first and never part of this list.
+MODES = ("adsb", "ais")
 
 # Which RTL-SDR index op25 holds is NOT fixed — on radio-box op25 had index 1
 # and index 0 was free, so "op25 is always 0" was wrong. rtlsdr can't open a
 # dongle another process has claimed, and the decoders exit within ~50ms when
-# that happens, so start() tries each index and keeps the first that stays up.
-# op25 is never disturbed: a failed claim doesn't touch its dongle.
+# that happens, so _start_one() tries each index and keeps the first that
+# stays up. op25 is never disturbed: a failed claim doesn't touch its dongle.
 MAX_SDR_INDEX = 4
 _STARTUP_GRACE_S = 2.0
 
-_PGID_FILE = "/tmp/secondary_sdr.pgid"
-_MODE_FILE = "/tmp/secondary_sdr.mode"
+_STATE_DIR = Path("/tmp/secondary_sdr")
 ADSB_JSON_DIR = Path("/tmp/adsb")
 
-# The live decoder handle. poll() is the only reliable liveness check: a
-# decoder that dies on startup (e.g. SDR busy) stays an unreaped zombie, and
-# killpg(pgid, 0) still succeeds on a zombie — status reported "running".
-_proc: Optional[subprocess.Popen] = None
+# Live decoder handles. poll() is the only reliable liveness check: a decoder
+# that dies on startup stays an unreaped zombie, and killpg(pgid, 0) still
+# succeeds on a zombie.
+_procs: Dict[str, subprocess.Popen] = {}
+_indices: Dict[str, int] = {}
+_lock = threading.Lock()
+
+# AIS-catcher streams one JSON object per received message on stdout rather
+# than writing a periodic snapshot file (readsb's approach) — so the
+# current-vessel snapshot lives in memory, keyed by mmsi, kept warm by a
+# background reader thread for as long as the decoder is alive.
+_ais_vessels: Dict[str, Dict[str, Any]] = {}
+_ais_lock = threading.Lock()
 
 
-def _save_state(pgid: int, mode: str) -> None:
-    Path(_PGID_FILE).write_text(str(pgid))
-    Path(_MODE_FILE).write_text(mode)
+def _pgid_file(mode: str) -> Path:
+    return _STATE_DIR / f"{mode}.pgid"
 
 
-def _read_pgid() -> Optional[int]:
+def _reap_orphans() -> None:
+    """Kill decoders left behind by a previous API process (uvicorn --reload
+    restarts this process, but decoders run in their own session and would
+    otherwise keep holding their SDRs)."""
+    if not _STATE_DIR.exists():
+        return
+    for f in _STATE_DIR.glob("*.pgid"):
         try:
-        return int(Path(_PGID_FILE).read_text().strip())
+            os.killpg(int(f.read_text().strip()), signal.SIGTERM)
+            LOGGER.info(f"Stopped orphaned secondary decoder from {f.name}")
         except Exception:
-        return None
+            pass
+        f.unlink(missing_ok=True)
 
 
-def _read_mode() -> Optional[str]:
-    try:
-        return Path(_MODE_FILE).read_text().strip()
-    except Exception:
-        return None
-
-
-def is_running() -> bool:
-    if _proc is not None:
-        return _proc.poll() is None
-    pgid = _read_pgid()
-    if pgid is None:
-        return False
-    try:
-        os.killpg(pgid, 0)
-        return True
-    except OSError:
-        return False
+_reap_orphans()
 
 
 def _adsb_command(index: int) -> List[str]:
@@ -86,10 +83,13 @@ def _ais_command(index: int) -> List[str]:
     return [
         "/opt/AIS-catcher/build/AIS-catcher",
         f"-d:{index}",  # "-d <x>" would select by serial, not index
-        "-o", "JSON",
+        "-o", "5",  # JSON Full: decoded fields (4 = sparse, "JSON" is rejected)
     ]
 
 
+_COMMANDS = {"adsb": _adsb_command, "ais": _ais_command}
+
+
 def _ais_reader(proc: subprocess.Popen) -> None:
     """
     Consume AIS-catcher's stdout, one JSON message per line, and keep the
@@ -134,25 +134,33 @@ def _ais_reader(proc: subprocess.Popen) -> None:
             _ais_vessels[str(mmsi)] = existing
 
 
-def start(mode: str) -> bool:
-    global _proc
-    if is_running():
-        stop()
+def is_running(mode: str) -> bool:
+    proc = _procs.get(mode)
+    return proc is not None and proc.poll() is None
 
-    if mode == "adsb":
-        build = _adsb_command
-    elif mode == "ais":
-        build = _ais_command
+
+def running() -> List[str]:
+    return [m for m in MODES if is_running(m)]
+
+
+def _start_one(mode: str, candidates: Optional[List[int]] = None) -> bool:
+    """Start one decoder on the first free SDR among `candidates` (default:
+    every index). False when none is free."""
+    if mode not in _COMMANDS:
+        raise ValueError(f"Unknown secondary SDR mode: {mode!r}")
+    if is_running(mode):
+        return True
+    if mode == "ais":
         with _ais_lock:
             _ais_vessels.clear()
-    else:
-        raise ValueError(f"Unknown secondary SDR mode: {mode!r}")
 
     needs_stdout = mode == "ais"
-    for index in range(MAX_SDR_INDEX):
+    for index in candidates if candidates is not None else range(MAX_SDR_INDEX):
+        if index in {_indices[m] for m in running() if m in _indices}:
+            continue
         try:
             proc = subprocess.Popen(
-                build(index),
+                _COMMANDS[mode](index),
                 preexec_fn=os.setsid,
                 stdout=subprocess.PIPE if needs_stdout else None,
                 text=True if needs_stdout else None,
@@ -169,46 +177,132 @@ def start(mode: str) -> bool:
             pass
         if needs_stdout:
             threading.Thread(target=_ais_reader, args=(proc,), daemon=True).start()
-        _proc = proc
-        _save_state(proc.pid, mode)
+        _procs[mode] = proc
+        _indices[mode] = index
+        _STATE_DIR.mkdir(parents=True, exist_ok=True)
+        _pgid_file(mode).write_text(str(proc.pid))
         LOGGER.info(f"Started secondary SDR decoder mode={mode!r} on SDR index {index} pid={proc.pid}")
         return True
 
-    LOGGER.error(f"Secondary SDR decoder mode={mode!r}: no free SDR found (op25 holds one; is a second plugged in?)")
+    LOGGER.info(f"Secondary SDR decoder mode={mode!r}: no free SDR left")
     return False
 
 
-def stop() -> bool:
-    global _proc
-    pgid = _read_pgid()
-    if pgid is None:
-        return True
+def _stop_one(mode: str) -> None:
+    proc = _procs.pop(mode, None)
+    _indices.pop(mode, None)
+    if proc is not None:
         try:
-        os.killpg(pgid, signal.SIGTERM)
+            os.killpg(proc.pid, signal.SIGTERM)
         except OSError:
             pass
-    if _proc is not None:
         try:
-            _proc.wait(timeout=5)
+            proc.wait(timeout=5)
         except subprocess.TimeoutExpired:
             pass
-        _proc = None
+    _pgid_file(mode).unlink(missing_ok=True)
+
+
+def start(mode: str) -> bool:
+    with _lock:
+        return _start_one(mode)
+
+
+def stop(mode: Optional[str] = None) -> None:
+    with _lock:
+        for m in [mode] if mode else list(_procs):
+            _stop_one(m)
+
+
+def _candidates(mode: str, pins: Dict[str, str], reserved: List[str], devs: List[Dict[str, Any]]) -> List[int]:
+    """SDR indices `mode` may use. A pinned mode gets exactly its dongle; an
+    unpinned one gets any dongle that isn't op25's (reserved) or pinned to
+    another service. Without enumeration, fall back to probing every index."""
+    if not devs:
+        return [] if pins.get(mode) else list(range(MAX_SDR_INDEX))
+    if pins.get(mode):
+        idx = _index_of(pins[mode], devs)
+        return [] if idx is None else [idx]
+    taken = set(reserved) | {s for m, s in pins.items() if m != mode and s}
+    return [d["index"] for d in devs if d["serial"] not in taken]
+
+
+def apply(priority: List[str], pins: Optional[Dict[str, str]] = None,
+          reserved: Optional[List[str]] = None) -> List[str]:
+    """Run decoders in priority order until SDRs run out; stop everything else.
+
+    `pins` maps a mode to the serial of the dongle carrying its antenna;
+    `reserved` lists serials no decoder may touch (op25's). Pins only bind
+    enabled modes — a disabled service's dongle is free for the others.
+    Unchanged when the right decoders already run on allowed dongles, so
+    re-applying the same settings is a no-op rather than a restart.
+    """
+    for m in priority:
+        if m not in _COMMANDS:
+            raise ValueError(f"Unknown secondary SDR mode: {m!r}")
+    pins = {m: s for m, s in (pins or {}).items() if m in priority and s}
+    reserved = [s for s in (reserved or []) if s]
+    devs = devices()
+    with _lock:
+        for m in running():
+            if m not in priority or _indices.get(m) not in _candidates(m, pins, reserved, devs):
+                _stop_one(m)
+        for i, m in enumerate(priority):
+            if m in running():
+                continue
+            cands = _candidates(m, pins, reserved, devs)
+            if _start_one(m, cands):
+                continue
+            # Out of free dongles: take one from the lowest-priority decoder
+            # holding a dongle this mode may use, which then gets its own turn.
+            lower = [x for x in priority[i + 1:] if x in running() and _indices.get(x) in cands]
+            if lower:
+                _stop_one(lower[-1])
+                _start_one(m, cands)
+        return running()
+
+
+def devices() -> List[Dict[str, Any]]:
+    """Every RTL-SDR on the node with its USB serial — readable even while a
+    dongle is claimed (op25's included), since it doesn't open the device.
+    Cheap dongles often ship with the same serial (00000001); those are
+    flagged, because pinning a service to a shared serial is ambiguous."""
     try:
-        os.remove(_PGID_FILE)
-    except OSError:
-        pass
-    try:
-        os.remove(_MODE_FILE)
-    except OSError:
-        pass
-    return True
+        lib = ctypes.CDLL(ctypes.util.find_library("rtlsdr") or "librtlsdr.so.0")
+        lib.rtlsdr_get_device_name.restype = ctypes.c_char_p
+        out = []
+        for i in range(lib.rtlsdr_get_device_count()):
+            manufact, product, serial = (ctypes.create_string_buffer(256) for _ in range(3))
+            lib.rtlsdr_get_device_usb_strings(i, manufact, product, serial)
+            out.append({
+                "index": i,
+                "serial": serial.value.decode(errors="replace") or None,
+                "name": (lib.rtlsdr_get_device_name(i) or b"").decode(errors="replace"),
+            })
+    except Exception as e:
+        LOGGER.warning(f"SDR enumeration failed: {e}")
+        return []
+    serials = [d["serial"] for d in out]
+    for d in out:
+        d["duplicate_serial"] = d["serial"] is not None and serials.count(d["serial"]) > 1
+    return out
+
+
+def _index_of(serial: str, devs: List[Dict[str, Any]]) -> Optional[int]:
+    """Index of a uniquely-identified serial; None if absent or ambiguous."""
+    matches = [d["index"] for d in devs if d["serial"] == serial]
+    return matches[0] if len(matches) == 1 else None
 
 
 def status() -> Dict[str, Any]:
-    running = is_running()
+    devs = devices()
+    by_index = {d["index"]: d["serial"] for d in devs}
     return {
-        "status": "running" if running else "stopped",
-        "mode": _read_mode() if running else None,
+        "running": [
+            {"mode": m, "sdr_index": _indices.get(m), "serial": by_index.get(_indices.get(m))} for m in running()
+        ],
+        "sdr_count": len(devs) if devs else None,
+        "devices": devs,
     }
 
 
@@ -250,11 +344,10 @@ def _read_adsb_snapshot() -> List[Dict[str, Any]]:
 
 
 def data() -> Dict[str, Any]:
-    mode = _read_mode()
-    if mode == "adsb":
-        return {"mode": mode, "aircraft": _read_adsb_snapshot()}
-    if mode == "ais":
     with _ais_lock:
-            vessels = list(_ais_vessels.values())
-        return {"mode": mode, "vessels": vessels}
-    return {"mode": mode, "aircraft": [], "vessels": []}
+        vessels = list(_ais_vessels.values()) if is_running("ais") else []
+    return {
+        "running": running(),
+        "aircraft": _read_adsb_snapshot() if is_running("adsb") else [],
+        "vessels": vessels,
+    }

secondary-sdr-container/app/routers/secondary_controller.py

@@ -1,3 +1,5 @@
+from typing import Dict, List, Optional
+
 from fastapi import APIRouter, HTTPException
 from pydantic import BaseModel
 
@@ -11,9 +13,27 @@ class StartBody(BaseModel):
     mode: str  # adsb | ais
 
 
+class StopBody(BaseModel):
+    mode: Optional[str] = None  # omit to stop every decoder
+
+
+class ApplyBody(BaseModel):
+    priority: List[str]  # ordered, e.g. ["adsb", "ais"]
+    pins: Dict[str, str] = {}  # mode -> serial of the dongle with its antenna
+    reserved: List[str] = []  # serials no decoder may touch (op25's)
+
+
 def create_secondary_router():
     router = APIRouter()
 
+    @router.post("/apply")
+    async def apply(body: ApplyBody):
+        try:
+            live = decoder_control.apply(body.priority, body.pins, body.reserved)
+        except ValueError as e:
+            raise HTTPException(status_code=400, detail=str(e))
+        return {"running": live}
+
     @router.post("/start")
     async def start(body: StartBody):
         try:
@@ -21,18 +41,22 @@ def create_secondary_router():
         except ValueError as e:
             raise HTTPException(status_code=400, detail=str(e))
         if not ok:
-            raise HTTPException(status_code=500, detail="Failed to start secondary SDR decoder")
+            raise HTTPException(status_code=409, detail="No free SDR for this decoder")
         return {"status": f"secondary SDR started ({body.mode})"}
 
     @router.post("/stop")
-    async def stop():
-        decoder_control.stop()
+    async def stop(body: Optional[StopBody] = None):
+        decoder_control.stop(body.mode if body else None)
         return {"status": "secondary SDR stopped"}
 
     @router.get("/status")
     async def get_status():
         return decoder_control.status()
 
+    @router.get("/devices")
+    async def get_devices():
+        return {"devices": decoder_control.devices()}
+
     @router.get("/data")
     async def get_data():
         return decoder_control.data()

secondary-sdr-container/tests/test_decoder_control.py

@@ -0,0 +1,84 @@
+"""
+node-26#11 — which dongle each secondary decoder may use.
+
+Run from secondary-sdr-container/:  PYTHONPATH=app python -m pytest -q tests
+"""
+from unittest.mock import patch
+
+import pytest
+
+from internal import decoder_control as dc
+
+# radio-box's real pair: op25's dongle and the one with the 1090 antenna.
+DEVS = [
+    {"index": 0, "serial": "69420", "name": "RTL", "duplicate_serial": False},
+    {"index": 1, "serial": "00000001", "name": "RTL", "duplicate_serial": False},
+]
+
+
+def test_unpinned_mode_never_gets_op25s_dongle():
+    assert dc._candidates("adsb", {}, ["00000001"], DEVS) == [0]
+
+
+def test_pinned_mode_gets_exactly_its_dongle():
+    assert dc._candidates("ais", {"ais": "69420"}, ["00000001"], DEVS) == [0]
+
+
+def test_unpinned_mode_skips_a_dongle_pinned_to_another_service():
+    assert dc._candidates("ais", {"adsb": "69420"}, ["00000001"], DEVS) == []
+
+
+def test_missing_or_ambiguous_pin_gets_nothing():
+    assert dc._candidates("adsb", {"adsb": "nope"}, [], DEVS) == []
+    dup = [dict(d, serial="00000001") for d in DEVS]
+    assert dc._candidates("adsb", {"adsb": "00000001"}, [], dup) == []
+
+
+class FakeDecoders:
+    """Stands in for real processes: one decoder per free index."""
+
+    def __init__(self):
+        self.live = {}
+
+    def start(self, mode, candidates=None):
+        free = [i for i in candidates if i not in self.live.values()]
+        if not free:
+            return False
+        self.live[mode] = free[0]
+        return True
+
+    def stop(self, mode):
+        self.live.pop(mode, None)
+
+
+@pytest.fixture
+def fake():
+    f = FakeDecoders()
+    with patch.object(dc, "devices", return_value=DEVS), \
+         patch.object(dc, "_start_one", side_effect=f.start), \
+         patch.object(dc, "_stop_one", side_effect=f.stop), \
+         patch.object(dc, "running", side_effect=lambda: [m for m in dc.MODES if m in f.live]), \
+         patch.dict(dc._indices, clear=True):
+        dc._indices.update(f.live)
+        yield f
+
+
+def _apply(fake, priority, pins=None):
+    dc.apply(priority, pins, ["00000001"])
+    dc._indices.clear()
+    dc._indices.update(fake.live)
+    return fake.live
+
+
+def test_one_spare_goes_to_the_top_pick(fake):
+    assert _apply(fake, ["ais", "adsb"]) == {"ais": 0}
+
+
+def test_reordering_hands_the_spare_to_the_new_top_pick(fake):
+    _apply(fake, ["adsb", "ais"])
+    assert _apply(fake, ["ais", "adsb"]) == {"ais": 0}
+
+
+def test_pinned_lower_priority_still_runs_when_top_pick_has_no_dongle(fake):
+    # AIS ranked first but its only candidate is ADS-B's pinned antenna dongle.
+    assert _apply(fake, ["ais", "adsb"], {"adsb": "69420"}) == {"adsb": 0}