diff --git a/schema2.sql b/schema2.sql
new file mode 100644
index 0000000..829b5f4
--- /dev/null
+++ b/schema2.sql
@@ -0,0 +1,163 @@
+begin;
+
+-- roles
+alter schema public owner to sensor_admin;
+grant usage on schema public to sensor_writer;
+
+grant all on all tables in schema public to sensor_admin;
+grant all on all sequences in schema public to sensor_admin;
+
+grant insert, update, select on all tables in schema public to sensor_writer;
+grant usage, select on all sequences in schema public to sensor_writer;
+
+alter default privileges for role sensor_admin in schema public
+    grant insert, update, select on tables to sensor_writer;
+
+alter default privileges for role sensor_admin in schema public
+    grant usage, select on sequences to sensor_writer;
+
+-- pg_partman
+create schema if not exists partman;
+create extension if not exists pg_partman schema partman;
+
+do $$
+begin
+  if not exists (select 1 from pg_roles where rolname = 'partman_user') then
+    create role partman_user with login;
+  end if;
+end$$;
+
+grant all on schema partman to partman_user;
+grant all on all tables in schema partman to partman_user;
+grant execute on all functions in schema partman to partman_user;
+grant execute on all procedures in schema partman to partman_user;
+
+grant all on schema public to partman_user;
+grant all on all tables in schema public to partman_user;
+grant temporary on database sensor_db to partman_user;
+grant create on database sensor_db to partman_user;
+
+grant usage, create on schema partman to sensor_admin;
+grant execute on all functions in schema partman to sensor_admin;
+grant all on all tables in schema partman to sensor_admin;
+grant all on all sequences in schema partman to sensor_admin;
+
+set role sensor_admin;
+
+-- physical/transport endpoints
+create table if not exists endpoints (
+    endpoint_id int primary key generated by default as identity,
+    endpoint_key text not null unique,
+
+    -- 'snmp' | 'mqtt' | 'visa'
+    protocol text not null,
+    conn jsonb not null default '{}'::jsonb,
+
+    is_enabled boolean not null default true,
+
+    created_at timestamptz not null default now(),
+    updated_at timestamptz not null default now()
+);
+
+create index if not exists idx_endpoints_enabled_protocol
+on endpoints (is_enabled, protocol);
+
+create table if not exists locations (
+    location_id int primary key generated by default as identity,
+    name text not null,
+    is_active bool not null default true,
+    constraint locations_name_unique unique (name)
+);
+
+create table if not exists devices (
+    device_id int primary key generated by default as identity,
+    -- "snmp:10.0.0.12:probe1"
+    -- "mqtt:esp32-1"
+    -- "visa:prologix:gpib5"
+    device_key text not null unique,
+
+    endpoint_id int references endpoints(endpoint_id),
+    location_id int references locations(location_id),
+    is_enabled boolean not null default true,
+
+    metadata jsonb not null default '{}'::jsonb,
+
+    created_at timestamptz not null default now(),
+    updated_at timestamptz not null default now()
+);
+
+create index if not exists idx_devices_endpoint on devices (endpoint_id);
+create index if not exists idx_devices_location on devices (location_id);
+create index if not exists idx_devices_enabled on devices (is_enabled);
+
+-- per-device measurement defs
+create table if not exists device_channels (
+    channel_id int primary key generated by default as identity,
+    device_id int not null references devices(device_id) on delete cascade,
+
+    -- corresponds to a column name in sensor_data (wide mapping)
+    metric text not null,
+
+    -- SNMP: {"type":"snmp_oid","oid":".1.3.6...","datatype":"float"}
+    -- MQTT: {"type":"mqtt_topic","topic":"sensors/x/telemetry","payload":"json","field":"temperature_c"}
+    -- VISA: {"type":"scpi","query":"MEAS:VOLT:DC?","read_termination":"\n"}
+    source jsonb not null,
+
+    scale_value double precision not null default 1.0,
+    offset_value double precision not null default 0.0,
+
+    poll_interval_s int,
+    is_enabled boolean not null default true,
+
+    created_at timestamptz not null default now(),
+
+    constraint device_channels_unique_metric unique (device_id, metric)
+);
+
+create index if not exists idx_device_channels_device on device_channels (device_id);
+
+-- device health/status
+create table if not exists device_status (
+    device_id int primary key references devices(device_id) on delete cascade,
+    last_seen timestamptz,
+    last_ok timestamptz,
+    last_error_at timestamptz,
+    last_error text,
+    updated_at timestamptz not null default now()
+);
+
+create table if not exists sensor_data (
+    ts          timestamptz not null,
+    device_id   int not null references devices(device_id),
+    location_id int references locations(location_id),
+
+    temp_c      real,
+    humidity_rh real,
+    pressure_pa real,
+    light_lux   real,
+    soil_moist  real,
+    co2_ppm     real,
+
+    voltage_v   real,
+    current_a   real,
+    resistance_ohm real,
+    freq_hz     real,
+    power_w     real,
+
+    constraint sensor_data_pk primary key (device_id, ts)
+) partition by range (ts);
+
+create index if not exists idx_sensor_data_device_ts on sensor_data (device_id, ts desc);
+create index if not exists idx_sensor_data_location_ts on sensor_data (location_id, ts desc);
+create index if not exists idx_sensor_data_ts_brin on sensor_data using brin(ts);
+
+-- partition
+select partman.create_parent(
+    p_parent_table  => 'public.sensor_data',
+    p_control       => 'ts',
+    p_interval      => '1 year',
+    p_premake       => 2
+);
+
+commit;
+
diff --git a/schema_reader.sql b/schema_reader.sql
new file mode 100644
index 0000000..9909e7b
--- /dev/null
+++ b/schema_reader.sql
@@ -0,0 +1,8 @@
+-- run as a privileged role (e.g., sensor_admin)
+create role sensor_reader login password 'GLuBeBFPZuxjru2OYiwlI1eT5Fg';
+
+grant usage on schema public to sensor_reader;
+grant select on all tables in schema public to sensor_reader;
+
+alter default privileges for role sensor_admin in schema public
+  grant select on tables to sensor_reader;
diff --git a/sensgw/db.py b/sensgw/db.py
index 35292d5..b98bc65 100644
--- a/sensgw/db.py
+++ b/sensgw/db.py
@@ -1,7 +1,6 @@
 # sensgw/db.py
 import asyncpg
 import json
-from typing import Optional
 
 
 async def _init_connection(con: asyncpg.Connection) -> None:
@@ -22,7 +21,7 @@ async def _init_connection(con: asyncpg.Connection) -> None:
 class Database:
     def __init__(self, dsn: str):
         self._dsn = dsn
-        self.pool: Optional[asyncpg.Pool] = None
+        self.pool: asyncpg.Pool | None = None
 
     async def start(self) -> None:
         self.pool = await asyncpg.create_pool(
@@ -36,4 +35,3 @@ class Database:
         if self.pool:
             await self.pool.close()
             self.pool = None
-
diff --git a/sensgw/main.py b/sensgw/main.py
index aa5981d..5f8f9de 100644
--- a/sensgw/main.py
+++ b/sensgw/main.py
@@ -4,15 +4,19 @@ from __future__ import annotations
 import asyncio
 import logging
 
+from sensgw.models import Endpoint
+
 from .config import load_config
 from .db import Database
 from .registry import load_registry
 from .writer import Writer
 
 from .protocols.mqtt import MqttCollector, MqttBinding
-from .protocols.prologix import PrologixEndpointCollector, PrologixBinding
+from .protocols.prologix import (
+    PrologixBinding,
+    PrologixEndpointLoop,
+)
 from .protocols.snmp import SnmpEndpointCollector, SnmpBinding
-# from .protocols.visa import VisaCollector, VisaBinding
 
 
 async def _run() -> None:
@@ -23,14 +27,13 @@ async def _run() -> None:
     db = Database(cfg.db_dsn)
     await db.start()
     writer = Writer(db)
+    tasks: list[asyncio.Task[None]] = []
 
     try:
         reg = await load_registry(db)
         by_proto = reg.channels_by_protocol()
 
-        tasks: list[asyncio.Task[None]] = []
-
-        # --- MQTT (assumes one broker; if multiple, split by endpoint_id) ---
+        #  MQTT
         mqtt_bindings: list[MqttBinding] = []
         for ep, dev, ch in by_proto.get("mqtt", []):
             src = ch.source
@@ -51,8 +54,8 @@ async def _run() -> None:
             mqttc = MqttCollector(writer)
             tasks.append(asyncio.create_task(mqttc.run(mqtt_bindings), name="mqtt"))
 
-        # --- SNMP (one task per endpoint) ---
-        snmp_bindings_by_ep: dict[int, tuple[object, list[SnmpBinding]]] = {}
+        # SNMP
+        snmp_bindings_by_ep: dict[int, tuple[Endpoint, list[SnmpBinding]]] = {}
         for ep, dev, ch in by_proto.get("snmp", []):
             src = ch.source
             if src.get("type") != "snmp_oid":
@@ -67,7 +70,9 @@ async def _run() -> None:
             )
             snmp_bindings_by_ep.setdefault(ep.endpoint_id, (ep, []))[1].append(b)
 
-        snmpc = SnmpEndpointCollector(writer, default_poll_s=cfg.default_poll_interval_s)
+        snmpc = SnmpEndpointCollector(
+            writer, default_poll_s=cfg.default_poll_interval_s
+        )
         for _ep_id, (ep, bindings) in snmp_bindings_by_ep.items():
             tasks.append(
                 asyncio.create_task(
@@ -76,53 +81,51 @@ async def _run() -> None:
                 )
             )
 
-        # --- Prologix (one task per channel/binding) ---
-        prolc = PrologixEndpointCollector(writer, default_poll_s=cfg.default_poll_interval_s)
+        # Prologix
+        # Group bindings by Endpoint ID
+        prologix_groups: dict[int, tuple[Endpoint, list[PrologixBinding]]] = {}
+
         for ep, dev, ch in by_proto.get("prologix", []):
             src = ch.source
             if src.get("type") != "scpi":
                 continue
+
             b = PrologixBinding(
-                endpoint=ep,
-                device=dev,
-                channel=ch,
-                query=str(src["query"]),
-                datatype=str(src.get("datatype", "float")),
-            )
-            tasks.append(
-                asyncio.create_task(
-                    prolc.run_binding(b),
-                    name=f"prologix:{dev.device_id}:{ch.metric}",
-                )
+                endpoint=ep, device=dev, channel=ch, query=str(src["query"])
             )
 
-        # --- VISA ---
-        # visac = VisaCollector(writer, default_poll_s=cfg.default_poll_interval_s)
-        # for ep, dev, ch in by_proto.get("visa", []):
-        #     src = ch.source
-        #     if src.get("type") != "scpi":
-        #         continue
-        #     b = VisaBinding(
-        #         endpoint=ep,
-        #         device=dev,
-        #         channel=ch,
-        #         query=str(src["query"]),
-        #         datatype=str(src.get("datatype", "float")),
-        #     )
-        #     tasks.append(
-        #         asyncio.create_task(
-        #             visac.run_binding(b),
-        #             name=f"visa:{dev.device_id}:{ch.metric}",
-        #         )
-        #     )
+            if ep.endpoint_id not in prologix_groups:
+                prologix_groups[ep.endpoint_id] = (ep, [])
+            prologix_groups[ep.endpoint_id][1].append(b)
+
+        # one Task per Endpoint
+        for _, (ep, bindings) in prologix_groups.items():
+            loop = PrologixEndpointLoop(
+                writer=writer,
+                endpoint=ep,
+                bindings=bindings,
+                default_poll_s=cfg.default_poll_interval_s,
+            )
+            tasks.append(
+                asyncio.create_task(loop.run(), name=f"prologix:{ep.endpoint_key}")
+            )
 
         if not tasks:
             log.warning("No enabled channels found. Exiting.")
             return
 
         log.info("Running with %d task(s)", len(tasks))
-        await asyncio.gather(*tasks)
+        _ = await asyncio.gather(*tasks)
+    except asyncio.CancelledError:
+        # clean exit on SIGINT
+        pass
+
     finally:
+        if tasks:
+            for t in tasks:
+                _ = t.cancel()
+            _ = await asyncio.gather(*tasks, return_exceptions=True)
+
         await db.stop()
 
 
diff --git a/sensgw/metrics.py b/sensgw/metrics.py
deleted file mode 100644
index 3ac8a91..0000000
--- a/sensgw/metrics.py
+++ /dev/null
@@ -1,13 +0,0 @@
-ALLOWED_METRICS = {
-    "temp_c",
-    "humidity_rh",
-    "pressure_pa",
-    "light_lux",
-    "soil_moist",
-    "co2_ppm",
-    "voltage_v",
-    "current_a",
-    "resistance_ohm",
-    "freq_hz",
-    "power_w",
-}
diff --git a/sensgw/models.py b/sensgw/models.py
index 2b4721c..be05615 100644
--- a/sensgw/models.py
+++ b/sensgw/models.py
@@ -1,6 +1,6 @@
 # sensgw/models.py
 from dataclasses import dataclass
-from typing import Any, Dict, Optional
+from typing import Any
 
 
 @dataclass(frozen=True)
@@ -8,7 +8,7 @@ class Endpoint:
     endpoint_id: int
     endpoint_key: str
     protocol: str
-    conn: Dict[str, Any]
+    conn: dict[str, Any]
     is_enabled: bool
 
 
@@ -16,10 +16,10 @@ class Endpoint:
 class Device:
     device_id: int
     device_key: str
-    endpoint_id: Optional[int]
-    location_id: Optional[int]
+    endpoint_id: int | None
+    location_id: int | None
     is_enabled: bool
-    metadata: Dict[str, Any]
+    metadata: dict[str, Any]
 
 
 @dataclass(frozen=True)
@@ -27,9 +27,8 @@ class Channel:
     channel_id: int
     device_id: int
     metric: str
-    source: Dict[str, Any]
+    source: dict[str, Any]
     scale_value: float
     offset_value: float
-    poll_interval_s: Optional[int]
+    poll_interval_s: int | None
     is_enabled: bool
-
diff --git a/sensgw/protocols/mqtt.py b/sensgw/protocols/mqtt.py
index bd84e42..51933eb 100644
--- a/sensgw/protocols/mqtt.py
+++ b/sensgw/protocols/mqtt.py
@@ -86,7 +86,7 @@ class MqttCollector:
         )
         c.on_message = self._on_message
 
-        # Optional auth
+        # auth?
         if "username" in ep.conn:
             c.username_pw_set(ep.conn["username"], ep.conn.get("password"))
 
diff --git a/sensgw/protocols/polling.py b/sensgw/protocols/polling.py
index c8c940c..811e9aa 100644
--- a/sensgw/protocols/polling.py
+++ b/sensgw/protocols/polling.py
@@ -1,7 +1,8 @@
 # sensgw/protocols/polling.py
 import asyncio
 import datetime as dt
-from typing import Awaitable, Callable, Optional
+from typing import Callable
+from collections.abc import Awaitable
 
 
 async def poll_forever(
@@ -9,7 +10,7 @@ async def poll_forever(
     interval_s: int,
     read_once: Callable[[], Awaitable[None]],
     jitter_s: float = 0.0,
-    stop_event: Optional[asyncio.Event] = None,
+    stop_event: asyncio.Event | None = None,
 ) -> None:
     if jitter_s:
         await asyncio.sleep(jitter_s)
diff --git a/sensgw/protocols/prologix.py b/sensgw/protocols/prologix.py
index a2de174..7c57ba6 100644
--- a/sensgw/protocols/prologix.py
+++ b/sensgw/protocols/prologix.py
@@ -3,13 +3,15 @@ from __future__ import annotations
 
 import asyncio
 import datetime as dt
-import threading
+import logging
+from collections import defaultdict
 from dataclasses import dataclass
 from typing import Any
 
 from ..models import Endpoint, Device, Channel
 from ..writer import Writer
-from .polling import poll_forever
+
+log = logging.getLogger(__name__)
 
 
 @dataclass(frozen=True)
@@ -18,169 +20,153 @@ class PrologixBinding:
     device: Device
     channel: Channel
     query: str
-    datatype: str  # "float" | "int" | ...
 
 
-def _parse_numeric(datatype: str, raw: str) -> float:
-    kind = (datatype or "float").strip().lower()
-    if kind == "int":
-        return float(int(raw))
-    # default: float
-    return float(raw)
-
-
-def _driver_class(driver_key: str) -> type[Any] | None:
-    """
-    Map driver keys stored in DB to PyMeasure instrument classes.
-
-    devices.metadata.driver examples:
-      - "keithley2000"
-    """
+def _driver_class(driver_key: str | None) -> type[Any] | None:
     key = (driver_key or "").strip().lower()
     if not key:
         return None
-
-    if key in {"keithley2000", "keithley_2000", "keithley:2000"}:
+    if key in {"keithley2000", "keithley_2000"}:
         from pymeasure.instruments.keithley import Keithley2000  # type: ignore
 
         return Keithley2000
-
-    # Add more mappings here as you add support.
     return None
 
 
-class PrologixEndpointClient:
+class PrologixEndpointLoop:
     """
-    One shared Prologix adapter per endpoint, protected by a lock because it is stateful
-    (address switching) and not safe to use concurrently.
-
-    If a device specifies devices.metadata.driver, we create a PyMeasure Instrument on top
-    of the same adapter and run queries through instrument.ask().
+    Manages one physical Prologix controller and sequentially polls its devices.
+    Merges connection state (Adapter) and logic (Collector) into one class.
     """
 
-    def __init__(self, endpoint: Endpoint):
+    def __init__(
+        self,
+        writer: Writer,
+        endpoint: Endpoint,
+        bindings: list[PrologixBinding],
+        default_poll_s: int,
+    ):
+        self.writer = writer
         self.endpoint = endpoint
-        self._lock = threading.Lock()
+        self.bindings = bindings
+        self.default_poll_s = default_poll_s
+
+        # conn state
         self._adapter: Any | None = None
         self._instruments: dict[tuple[int, str], Any] = {}
+        self._initialized_addrs: set[int] = set()
 
     def _get_adapter(self) -> Any:
         if self._adapter is None:
             from pymeasure.adapters import PrologixAdapter  # type: ignore
 
-            try:
-                resource = self.endpoint.conn["resource"]
-            except KeyError as e:
-                raise RuntimeError(
-                    f"Missing endpoint.conn['resource'] for endpoint_id={self.endpoint.endpoint_id}"
-                ) from e
+            res = self.endpoint.conn["resource"]
+            to_ms = int(self.endpoint.conn.get("gpib_read_timeout_ms", 500))
 
-            read_timeout = int(self.endpoint.conn.get("gpib_read_timeout_ms", 200))
-            auto = bool(self.endpoint.conn.get("auto", False))
+            # auto=False gives us manual control over addressing
+            self._adapter = PrologixAdapter(res, gpib_read_timeout=to_ms, auto=False)
 
-            self._adapter = PrologixAdapter(
-                resource,
-                gpib_read_timeout=read_timeout,
-                auto=auto,
-            )
             try:
                 self._adapter.flush_read_buffer()
             except Exception:
                 pass
         return self._adapter
 
-    def _get_instrument(self, *, gpib_addr: int, driver_key: str) -> Any:
-        """
-        Cached per (addr, driver_key). Uses the shared adapter.
-        """
-        key = (gpib_addr, driver_key.strip().lower())
-        inst = self._instruments.get(key)
-        if inst is not None:
-            return inst
+    def _get_instrument(self, gpib_addr: int, driver_key: str) -> Any:
+        cache_key = (gpib_addr, driver_key)
+        if cache_key in self._instruments:
+            return self._instruments[cache_key]
 
         cls = _driver_class(driver_key)
-        if cls is None:
-            raise KeyError(f"Unknown driver '{driver_key}'")
+        if not cls:
+            raise ValueError(f"Unknown driver: {driver_key}")
 
         ad = self._get_adapter()
-        # Ensure the adapter is pointed at the correct instrument when the driver is constructed.
         ad.address = gpib_addr
-
         inst = cls(ad)
-        self._instruments[key] = inst
+
+        self._instruments[cache_key] = inst
         return inst
 
-    def query(self, *, gpib_addr: int, cmd: str, driver_key: str | None = None) -> str:
-        """
-        Execute a query at a given GPIB address.
-        If driver_key is provided and known, execute via driver (instrument.ask).
-        Otherwise, raw adapter write/read.
-        """
-        with self._lock:
+    def _exec_sync(self, gpib_addr: int, query: str, driver_key: str | None) -> str:
+        # init hw
+        if gpib_addr not in self._initialized_addrs:
+            dk_check = (driver_key or "").lower()
+            if "keithley" in dk_check:
+                try:
+                    log.info(f"Initializing Keithley @ {gpib_addr} (DISP:ENAB OFF)")
+                    if driver_key:
+                        inst = self._get_instrument(gpib_addr, driver_key)
+                        inst.write(":DISP:ENAB OFF")
+                    else:
+                        ad = self._get_adapter()
+                        ad.address = gpib_addr
+                        ad.write(":DISP:ENAB OFF")
+                except Exception as e:
+                    log.warning(f"VFD saver failed for {gpib_addr}: {e}")
+            self._initialized_addrs.add(gpib_addr)
+
+        # Query
+        if driver_key:
+            inst = self._get_instrument(gpib_addr, driver_key)
+            # re-assert address in case it chnaged
+            self._get_adapter().address = gpib_addr
+            return str(inst.ask(query)).strip()
+        else:
             ad = self._get_adapter()
             ad.address = gpib_addr
-
-            if driver_key:
-                inst = self._get_instrument(gpib_addr=gpib_addr, driver_key=driver_key)
-                # Keep the endpoint lock held across ask(); it may do multiple I/O ops.
-                return str(inst.ask(cmd)).strip()
-
-            ad.write(cmd)
+            ad.write(query)
             return str(ad.read()).strip()
 
+    async def run(self) -> None:
+        log.info(
+            f"Starting Prologix loop: {self.endpoint.endpoint_key} ({len(self.bindings)} bindings)"
+        )
 
-class PrologixEndpointCollector:
-    def __init__(self, writer: Writer, default_poll_s: int):
-        self.writer = writer
-        self.default_poll_s = default_poll_s
-        self._clients: dict[int, PrologixEndpointClient] = {}
+        # group by device
+        by_device = defaultdict(list)
+        for b in self.bindings:
+            by_device[b.device.device_id].append(b)
 
-    def _client(self, endpoint: Endpoint) -> PrologixEndpointClient:
-        client = self._clients.get(endpoint.endpoint_id)
-        if client is None:
-            client = PrologixEndpointClient(endpoint)
-            self._clients[endpoint.endpoint_id] = client
-        return client
+        while True:
+            start_ts = asyncio.get_running_loop().time()
 
-    async def run_binding(self, b: PrologixBinding) -> None:
-        interval_s = int(b.channel.poll_interval_s or self.default_poll_s)
-        client = self._client(b.endpoint)
+            for _dev_id, dev_bindings in by_device.items():
+                # validation
+                meta = dev_bindings[0].device.metadata
+                gpib_addr = meta.get("gpib_addr")
+                if gpib_addr is None:
+                    continue
 
-        gpib_addr = b.device.metadata.get("gpib_addr")
-        if gpib_addr is None:
-            raise RuntimeError(
-                f"Missing device.metadata.gpib_addr for device_id={b.device.device_id}"
-            )
-        gpib_addr = int(gpib_addr)
+                gpib_addr = int(gpib_addr)
+                driver_key = str(meta.get("driver", "")).strip() or None
 
-        driver_key = b.device.metadata.get("driver")
-        driver_key = str(driver_key).strip() if driver_key else None
+                for b in dev_bindings:
+                    try:
+                        # offload to thread
+                        raw = await asyncio.to_thread(
+                            self._exec_sync, gpib_addr, b.query, driver_key
+                        )
 
-        async def read_once() -> None:
-            ts = dt.datetime.now(dt.timezone.utc)
-            try:
-                raw = await asyncio.to_thread(
-                    client.query,
-                    gpib_addr=gpib_addr,
-                    cmd=b.query,
-                    driver_key=driver_key,
-                )
+                        val = float(raw)
+                        val = val * b.channel.scale_value + b.channel.offset_value
 
-                v = _parse_numeric(b.datatype, raw)
-                v = v * b.channel.scale_value + b.channel.offset_value
+                        await self.writer.write_metric(
+                            ts=dt.datetime.now(dt.timezone.utc),
+                            device_id=b.device.device_id,
+                            location_id=b.device.location_id,
+                            metric=b.channel.metric,
+                            value=val,
+                        )
+                    except Exception as e:
+                        log.error(
+                            f"Prologix error {b.device.device_key}/{b.channel.metric}: {e}"
+                        )
+                        await self.writer.write_error(
+                            device_id=b.device.device_id, error=f"prologix: {e}"
+                        )
 
-                await self.writer.write_metric(
-                    ts=ts,
-                    device_id=b.device.device_id,
-                    location_id=b.device.location_id,
-                    metric=b.channel.metric,
-                    value=v,
-                )
-            except Exception as e:
-                await self.writer.write_error(
-                    device_id=b.device.device_id,
-                    error=f"prologix: {e}",
-                )
-
-        await poll_forever(interval_s=interval_s, read_once=read_once)
+                await asyncio.sleep(0)
 
+            elapsed = asyncio.get_running_loop().time() - start_ts
+            await asyncio.sleep(max(0.5, self.default_poll_s - elapsed))
diff --git a/sensgw/protocols/snmp.py b/sensgw/protocols/snmp.py
index 5ef664d..6f3a718 100644
--- a/sensgw/protocols/snmp.py
+++ b/sensgw/protocols/snmp.py
@@ -4,6 +4,16 @@ from __future__ import annotations
 import datetime as dt
 from dataclasses import dataclass
 
+from pysnmp.hlapi.v3arch.asyncio import (
+    SnmpEngine,
+    CommunityData,
+    UdpTransportTarget,
+    ContextData,
+    ObjectType,
+    ObjectIdentity,
+    get_cmd,
+)
+
 from ..models import Endpoint, Device, Channel
 from ..writer import Writer
 from .polling import poll_forever
@@ -15,7 +25,7 @@ class SnmpBinding:
     device: Device
     channel: Channel
     oid: str
-    datatype: str  # "float" | "int" | ...
+    datatype: str
 
 
 def _parse_numeric(datatype: str, raw: str) -> float:
@@ -26,11 +36,6 @@ def _parse_numeric(datatype: str, raw: str) -> float:
 
 
 def _parse_version(conn: dict) -> int:
-    """
-    Return mpModel:
-      SNMPv1  -> 0
-      SNMPv2c -> 1
-    """
     v = str(conn.get("version", "2c")).lower()
     if v in {"1", "v1", "snmpv1"}:
         return 0
@@ -41,6 +46,10 @@ class SnmpEndpointCollector:
     def __init__(self, writer: Writer, default_poll_s: int):
         self.writer = writer
         self.default_poll_s = default_poll_s
+        self._engine = SnmpEngine()
+
+    async def close(self):
+        self._engine.close_dispatcher()
 
     async def _get_many(
         self,
@@ -52,52 +61,44 @@ class SnmpEndpointCollector:
         timeout_s: int,
         oids: list[str],
     ) -> dict[str, str]:
-        from pysnmp.hlapi.v3arch.asyncio import (  # type: ignore
-            SnmpEngine,
-            CommunityData,
-            UdpTransportTarget,
-            ContextData,
-            ObjectType,
-            ObjectIdentity,
-            get_cmd,
+        snmp_engine = self._engine
+
+        var_binds = [ObjectType(ObjectIdentity(oid)) for oid in oids]
+        target = await UdpTransportTarget.create(
+            (host, port), timeout=timeout_s, retries=0
         )
 
-        snmp_engine = SnmpEngine()
-        try:
-            var_binds = [ObjectType(ObjectIdentity(oid)) for oid in oids]
+        iterator = get_cmd(
+            snmp_engine,
+            CommunityData(community, mpModel=mp_model),
+            target,
+            ContextData(),
+            *var_binds,
+        )
 
-            # In pysnmp 7.x, target creation is async:
-            target = await UdpTransportTarget.create((host, port), timeout=timeout_s, retries=0)
+        # await the response
+        error_indication, error_status, error_index, out_binds = await iterator
 
-            iterator = get_cmd(
-                snmp_engine,
-                CommunityData(community, mpModel=mp_model),
-                target,
-                ContextData(),
-                *var_binds,
-            )
+        if error_indication:
+            raise RuntimeError(str(error_indication))
 
-            error_indication, error_status, error_index, out_binds = await iterator
+        if error_status:
+            idx = int(error_index) - 1
+            oid_caused = out_binds[idx][0] if 0 <= idx < len(out_binds) else "?"
+            raise RuntimeError(f"{str(error_status)} at {oid_caused}")
 
-            if error_indication:
-                raise RuntimeError(str(error_indication))
-            if error_status:
-                raise RuntimeError(
-                    f"{error_status.prettyPrint()} at "
-                    f"{out_binds[int(error_index) - 1][0] if error_index else '?'}"
-                )
+        return {str(name): str(val) for name, val in out_binds}
 
-            return {str(name): str(val) for name, val in out_binds}
-        finally:
-            snmp_engine.close_dispatcher()
-
-    async def run_endpoint(self, endpoint: Endpoint, bindings: list[SnmpBinding]) -> None:
+    async def run_endpoint(
+        self, endpoint: Endpoint, bindings: list[SnmpBinding]
+    ) -> None:
         host = endpoint.conn["host"]
         port = int(endpoint.conn.get("port", 161))
         community = endpoint.conn.get("community", "public")
         timeout_s = int(endpoint.conn.get("timeout_s", 2))
         mp_model = _parse_version(endpoint.conn)
 
+        # if one channel is 1s and another is 60s, we poll ALL at 1s.
         intervals = [
             int(b.channel.poll_interval_s)
             for b in bindings
@@ -105,6 +106,7 @@ class SnmpEndpointCollector:
         ]
         interval_s = min(intervals) if intervals else self.default_poll_s
 
+        # map clean string OIDs to bindings
         oid_to_binding: dict[str, SnmpBinding] = {b.oid.strip(): b for b in bindings}
         oids = list(oid_to_binding.keys())
 
@@ -124,6 +126,7 @@ class SnmpEndpointCollector:
                     b = oid_to_binding.get(oid_str)
                     if b is None:
                         continue
+
                     try:
                         v = _parse_numeric(b.datatype, raw)
                         v = v * b.channel.scale_value + b.channel.offset_value
@@ -138,15 +141,14 @@ class SnmpEndpointCollector:
                     except Exception as e:
                         await self.writer.write_error(
                             device_id=b.device.device_id,
-                            error=f"snmp parse/write: {e}",
+                            error=f"snmp parse: {e}",
                         )
             except Exception as e:
-                # Endpoint-level failure: mark all devices as error
+                # log endpoint-level failure
                 for b in bindings:
                     await self.writer.write_error(
                         device_id=b.device.device_id,
-                        error=f"snmp endpoint: {e}",
+                        error=f"snmp fetch: {e}",
                     )
 
         await poll_forever(interval_s=interval_s, read_once=read_once)
-
diff --git a/sensgw/protocols/visa.py b/sensgw/protocols/visa.py
deleted file mode 100644
index ee2bebb..0000000
--- a/sensgw/protocols/visa.py
+++ /dev/null
@@ -1,84 +0,0 @@
-# sensgw/protocols/visa.py
-from __future__ import annotations
-
-import asyncio
-import datetime as dt
-from dataclasses import dataclass
-
-from ..models import Endpoint, Device, Channel
-from ..writer import Writer
-from .polling import poll_forever
-
-
-@dataclass(frozen=True)
-class VisaBinding:
-    endpoint: Endpoint
-    device: Device
-    channel: Channel
-    query: str
-    datatype: str  # "float" etc
-
-
-def _visa_query_sync(*, resource: str, conn: dict, device_meta: dict, query: str) -> str:
-    import pyvisa  # type: ignore
-
-    rm = pyvisa.ResourceManager()
-    inst = rm.open_resource(resource)
-
-    # Optional serial config
-    if "baud_rate" in conn and hasattr(inst, "baud_rate"):
-        inst.baud_rate = int(conn["baud_rate"])
-
-    if "read_termination" in conn:
-        inst.read_termination = str(conn["read_termination"])
-    if "write_termination" in conn:
-        inst.write_termination = str(conn["write_termination"])
-
-    # If you're using a Prologix-like controller over serial, you may need to set addr.
-    # This is device-specific; keeping it optional:
-    gpib_addr = device_meta.get("gpib_addr")
-    if gpib_addr is not None:
-        inst.write(f"++addr {int(gpib_addr)}")
-
-    return str(inst.query(query)).strip()
-
-
-class VisaCollector:
-    def __init__(self, writer: Writer, default_poll_s: int):
-        self.writer = writer
-        self.default_poll_s = default_poll_s
-
-    async def run_binding(self, b: VisaBinding) -> None:
-        ep = b.endpoint
-        resource = ep.conn["resource"]
-        interval_s = int(b.channel.poll_interval_s or self.default_poll_s)
-
-        async def read_once() -> None:
-            try:
-                raw = await asyncio.to_thread(
-                    _visa_query_sync,
-                    resource=resource,
-                    conn=ep.conn,
-                    device_meta=b.device.metadata,
-                    query=b.query,
-                )
-                if b.datatype == "float":
-                    value = float(raw)
-                elif b.datatype == "int":
-                    value = float(int(raw))
-                else:
-                    value = float(raw)
-
-                value = value * b.channel.scale_value + b.channel.offset_value
-                ts = dt.datetime.now(dt.timezone.utc)
-                await self.writer.write_metric(
-                    ts=ts,
-                    device_id=b.device.device_id,
-                    location_id=b.device.location_id,
-                    metric=b.channel.metric,
-                    value=value,
-                )
-            except Exception as e:
-                await self.writer.write_error(device_id=b.device.device_id, error=f"visa: {e}")
-
-        await poll_forever(interval_s=interval_s, read_once=read_once)
diff --git a/sensgw/registry.py b/sensgw/registry.py
index a94ffec..81c9d6a 100644
--- a/sensgw/registry.py
+++ b/sensgw/registry.py
@@ -1,6 +1,5 @@
 # sensgw/registry.py
 from dataclasses import dataclass
-from typing import Dict, List, Tuple
 
 from .models import Endpoint, Device, Channel
 from .db import Database
@@ -8,12 +7,12 @@ from .db import Database
 
 @dataclass(frozen=True)
 class Registry:
-    endpoints: Dict[int, Endpoint]
-    devices: Dict[int, Device]
-    channels: List[Channel]
+    endpoints: dict[int, Endpoint]
+    devices: dict[int, Device]
+    channels: list[Channel]
 
-    def channels_by_protocol(self) -> Dict[str, List[Tuple[Endpoint, Device, Channel]]]:
-        out: Dict[str, List[Tuple[Endpoint, Device, Channel]]] = {}
+    def channels_by_protocol(self) -> dict[str, list[tuple[Endpoint, Device, Channel]]]:
+        out: dict[str, list[tuple[Endpoint, Device, Channel]]] = {}
         for ch in self.channels:
             dev = self.devices.get(ch.device_id)
             if not dev or not dev.is_enabled or dev.endpoint_id is None:
@@ -67,8 +66,12 @@ async def load_registry(db: Database) -> Registry:
         int(r["device_id"]): Device(
             device_id=int(r["device_id"]),
             device_key=str(r["device_key"]),
-            endpoint_id=(int(r["endpoint_id"]) if r["endpoint_id"] is not None else None),
-            location_id=(int(r["location_id"]) if r["location_id"] is not None else None),
+            endpoint_id=(
+                int(r["endpoint_id"]) if r["endpoint_id"] is not None else None
+            ),
+            location_id=(
+                int(r["location_id"]) if r["location_id"] is not None else None
+            ),
             is_enabled=bool(r["is_enabled"]),
             metadata=(r["metadata"] or {}),
         )
@@ -83,11 +86,12 @@ async def load_registry(db: Database) -> Registry:
             source=(r["source"] or {}),
             scale_value=float(r["scale_value"]),
             offset_value=float(r["offset_value"]),
-            poll_interval_s=(int(r["poll_interval_s"]) if r["poll_interval_s"] is not None else None),
+            poll_interval_s=(
+                int(r["poll_interval_s"]) if r["poll_interval_s"] is not None else None
+            ),
             is_enabled=bool(r["is_enabled"]),
         )
         for r in ch_rows
     ]
 
     return Registry(endpoints=endpoints, devices=devices, channels=channels)
-
diff --git a/sensgw/writer.py b/sensgw/writer.py
index 869e128..880526e 100644
--- a/sensgw/writer.py
+++ b/sensgw/writer.py
@@ -2,10 +2,22 @@
 from __future__ import annotations
 
 import datetime as dt
-from typing import Optional
 
 from .db import Database
-from .metrics import ALLOWED_METRICS
+
+ALLOWED_METRICS = {
+    "temp_c",
+    "humidity_rh",
+    "pressure_pa",
+    "light_lux",
+    "soil_moist",
+    "co2_ppm",
+    "voltage_v",
+    "current_a",
+    "resistance_ohm",
+    "freq_hz",
+    "power_w",
+}
 
 
 class Writer:
@@ -17,7 +29,7 @@ class Writer:
         *,
         ts: dt.datetime,
         device_id: int,
-        location_id: Optional[int],
+        location_id: int | None,
         metric: str,
         value: float,
     ) -> None: