Auto: s7-c3 — per-tag scan group / publish rate

Closes #296

docs/v2/s7.md

@@ -573,6 +573,101 @@ S7 driver health without reaching for a Wireshark capture:
 The values render alongside Modbus / OPC UA Client metrics in the Admin
 UI driver-diagnostics panel — same RPC, same dashboard row layout.
 
+### Per-tag scan groups
+
+Before PR-S7-C3, `ISubscribable.SubscribeAsync` took **one** publishing
+interval and applied it to every tag in the input list. A site that wanted
+mixed cadences — say a 100 ms HMI pulse, a 1 s dashboard tile, and a 10 s
+slow-poll for trend data — had to issue **three separate subscribe calls**,
+each with its own list of tags. That works, but it pushes the partitioning
+problem up to the caller (the OPC UA address space layer) and means an
+operator can't express "this tag is slow-poll" purely in driver config.
+
+PR-S7-C3 adds **per-tag scan groups** so a single `SubscribeAsync` call
+naturally splits into N independent poll loops:
+
+- `S7TagDefinition.ScanGroup` (string, optional) — the group identifier the
+  tag belongs to. Tags with no group (or with a group not declared in the
+  rate map below) keep the legacy behaviour and inherit the
+  subscription-default publishing interval.
+- `S7DriverOptions.ScanGroupIntervals` (`IReadOnlyDictionary<string, TimeSpan>`,
+  optional) — the rate map. Group names are matched case-insensitively. Any
+  group with a non-positive interval (≤ 0 ms) is silently dropped at config
+  load and tags falling back to that group land in the default partition.
+
+At subscribe time the driver buckets the input tag list by **resolved
+publishing interval** (per-tag group → map lookup → fallback to the
+subscription default), then spins up one background poll loop per distinct
+interval. Each loop owns its own `CancellationTokenSource` and its own
+`LastValues` cache; `UnsubscribeAsync` cancels and disposes every per-group
+loop together so a multi-rate subscription can't leak background tasks.
+
+#### JSON config example
+
+```json
+{
+  "Host": "10.0.0.50",
+  "ScanGroupIntervalsMs": {
+    "Fast":   100,
+    "Medium": 1000,
+    "Slow":   10000
+  },
+  "Tags": [
+    { "Name": "PressureSetpoint", "Address": "DB1.DBW0",  "DataType": "Int16",   "ScanGroup": "Fast"   },
+    { "Name": "BatchTotal",       "Address": "DB1.DBD10", "DataType": "Int32",   "ScanGroup": "Medium" },
+    { "Name": "TrendBucket",      "Address": "DB1.DBD20", "DataType": "Float32", "ScanGroup": "Slow"   }
+  ]
+}
+```
+
+A single `SubscribeAsync(["PressureSetpoint","BatchTotal","TrendBucket"], 1s)`
+call against this driver produces **three independent poll loops** —
+the fast HMI tag ticks at 100 ms, the dashboard tile at 1 s, the trend
+bucket at 10 s. The caller-supplied 1 s default is unused because every
+tag carries an explicit group.
+
+#### 100 ms floor applies per partition
+
+The `100 ms` floor that protects the S7 mailbox from sub-scan polling
+applies to **both** the subscription default **and** every per-group rate.
+A typo'd entry like `{"TooFast": 25}` is silently floored to 100 ms at
+partition-build time — the driver never schedules a sub-100 ms `Task.Delay`
+even if the operator tries.
+
+#### `_gate` contention caveat — "1 connection / 1 mailbox"
+
+Partitioning into N poll loops does **not** parallelise wire-level reads.
+S7netplus's documented pattern is one `Plc` instance per CPU, and the
+driver enforces that with a per-instance `SemaphoreSlim` (`_gate`) that
+every read takes before touching the socket. All N partitions share the
+same gate, so the **mailbox is still strictly serial** — what the multi-rate
+split actually buys you is **cadence decoupling**:
+
+- Before PR-S7-C3: every tag ticked at the slowest configured interval (or
+  required three separate subscribe calls and three separate logical
+  subscription handles, complicating the address-space layer).
+- After PR-S7-C3: a 100 ms HMI tag isn't blocked behind a 10 s slow-poll
+  batch's `Task.Delay`. While Slow is sleeping, the gate is free and Fast
+  acquires it, polls, releases. The CPU sees more frequent small requests
+  rather than infrequent large ones — which is what you want for a
+  responsive HMI surface.
+
+The caveat to be aware of: if Fast's per-tick read takes longer than its
+tick interval (e.g. 100 ms tick but 200 ms gate-held read because Medium
+or Slow happens to be mid-read on the gate), Fast's effective cadence
+slows to "as fast as the gate lets me." That's a property of S7netplus's
+single-connection design, not of partitioning — three separate driver
+instances against the same CPU would just waste the CPU's
+8-64-connection-resource budget without speeding anything up.
+
+#### Diagnostics
+
+Partition counts aren't yet surfaced under
+`DriverHealth.Diagnostics` (planned for a follow-up alongside per-partition
+tick rate). Tests can call the internal helpers `S7Driver.GetPartitionCount`
+and `S7Driver.GetPartitionSummary` to inspect the resolved partitioning of
+a live subscription handle.
+
 ## TSAP / Connection Type
 
 S7comm runs on top of ISO-on-TCP (RFC 1006), and the COTP connection-request

src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs

@@ -215,10 +215,15 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
         _probeCts?.Dispose();
         _probeCts = null;
 
+        // PR-S7-C3 — every subscription owns N partition CTSs; tear them all down so a
+        // shutdown mid-poll doesn't leave background tasks running against a closed Plc.
         foreach (var state in _subscriptions.Values)
         {
-            try { state.Cts.Cancel(); } catch { }
+            foreach (var part in state.Partitions)
-            state.Cts.Dispose();
+            {
+                try { part.Cts.Cancel(); } catch { }
+                part.Cts.Dispose();
+            }
         }
         _subscriptions.Clear();
 
@@ -1160,20 +1165,66 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
 
     // ---- ISubscribable (polling overlay) ----
 
+    /// <summary>
+    ///     PR-S7-C3 — partitions <paramref name="fullReferences"/> by resolved publishing
+    ///     interval (per-tag <see cref="S7TagDefinition.ScanGroup"/> looked up in
+    ///     <see cref="S7DriverOptions.ScanGroupIntervals"/>, falling back to
+    ///     <paramref name="publishingInterval"/>) and starts one background poll loop per
+    ///     distinct interval. The returned <see cref="ISubscriptionHandle"/> is one logical
+    ///     subscription that owns N partition loops; <see cref="UnsubscribeAsync"/> tears
+    ///     them all down together.
+    /// </summary>
+    /// <remarks>
+    ///     Each partition shares the per-driver <c>_gate</c> semaphore, so wire-level reads
+    ///     stay strictly serial — the multi-rate split decouples tick cadence (a fast HMI tag
+    ///     isn't blocked behind a slow batch's <c>Task.Delay</c>) but does NOT parallelise
+    ///     mailbox traffic. The "1 connection / 1 mailbox" caveat is documented in
+    ///     <c>docs/v2/s7.md</c>.
+    /// </remarks>
     public Task<ISubscriptionHandle> SubscribeAsync(
         IReadOnlyList<string> fullReferences, TimeSpan publishingInterval, CancellationToken cancellationToken)
     {
         var id = Interlocked.Increment(ref _nextSubscriptionId);
-        var cts = new CancellationTokenSource();
-        // Floor at 100 ms — S7 CPUs scan 2-10 ms but the comms mailbox is processed at most
-        // once per scan; sub-100 ms polling just queues wire-side with worse latency.
-        var interval = publishingInterval < TimeSpan.FromMilliseconds(100)
-            ? TimeSpan.FromMilliseconds(100)
-            : publishingInterval;
         var handle = new S7SubscriptionHandle(id);
-        var state = new SubscriptionState(handle, [.. fullReferences], interval, cts);
+
+        // Floor at 100 ms — S7 CPUs scan 2-10 ms but the comms mailbox is processed at most
+        // once per scan; sub-100 ms polling just queues wire-side with worse latency. The
+        // floor applies to BOTH the subscribe-default interval AND any per-group override
+        // so a misconfigured group can't slip below the protective bound.
+        var defaultInterval = ApplyMinInterval(publishingInterval);
+
+        // Bucket tags by resolved interval. Tags with no ScanGroup, or with a group not in
+        // the rate map, fall back to the subscription-default rate. This preserves the
+        // legacy single-rate path: an unconfigured driver gets exactly one partition.
+        var partitions = new Dictionary<TimeSpan, List<string>>();
+        foreach (var tagRef in fullReferences)
+        {
+            var interval = ResolveInterval(tagRef, defaultInterval);
+            if (!partitions.TryGetValue(interval, out var list))
+            {
+                list = [];
+                partitions[interval] = list;
+            }
+            list.Add(tagRef);
+        }
+
+        var partitionStates = new List<PartitionState>(partitions.Count);
+        foreach (var (interval, refs) in partitions)
+        {
+            var partCts = new CancellationTokenSource();
+            var part = new PartitionState(refs, interval, partCts);
+            partitionStates.Add(part);
+        }
+
+        var state = new SubscriptionState(handle, [.. fullReferences], defaultInterval, partitionStates);
         _subscriptions[id] = state;
-        _ = Task.Run(() => PollLoopAsync(state, cts.Token), cts.Token);
+
+        // Start each partition loop AFTER the state is registered so an early UnsubscribeAsync
+        // (e.g. the OPC UA stack tearing the session down on session cancel) doesn't race
+        // ahead of the partitions' Task.Run kickoff.
+        foreach (var part in partitionStates)
+            _ = Task.Run(() => PollLoopAsync(handle, part, part.Cts.Token), part.Cts.Token);
+
         return Task.FromResult<ISubscriptionHandle>(handle);
     }
 
@@ -1181,49 +1232,135 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
     {
         if (handle is S7SubscriptionHandle h && _subscriptions.TryRemove(h.Id, out var state))
         {
-            state.Cts.Cancel();
+            foreach (var part in state.Partitions)
-            state.Cts.Dispose();
+            {
+                try { part.Cts.Cancel(); } catch { }
+                part.Cts.Dispose();
+            }
         }
         return Task.CompletedTask;
     }
 
-    private async Task PollLoopAsync(SubscriptionState state, CancellationToken ct)
+    /// <summary>
+    ///     Apply the 100 ms floor to a caller-supplied publishing interval. Internal so
+    ///     <see cref="SubscribeAsync"/> can guard both the default + every per-group rate.
+    /// </summary>
+    private static TimeSpan ApplyMinInterval(TimeSpan requested) =>
+        requested < TimeSpan.FromMilliseconds(100) ? TimeSpan.FromMilliseconds(100) : requested;
+
+    /// <summary>
+    ///     Resolve the publishing interval for one tag — <see cref="S7DriverOptions.ScanGroupIntervals"/>
+    ///     wins when the tag's <see cref="S7TagDefinition.ScanGroup"/> is present, otherwise
+    ///     fall back to the subscription default. Unknown tags (not in the driver's map)
+    ///     fall back to the default — the poll loop will surface them as BadNodeIdUnknown
+    ///     anyway via <see cref="ReadAsync"/>.
+    /// </summary>
+    internal TimeSpan ResolveInterval(string tagRef, TimeSpan defaultInterval)
     {
-        // Initial-data push per OPC UA Part 4 convention.
+        if (_options.ScanGroupIntervals is { Count: > 0 } map &&
-        try { await PollOnceAsync(state, forceRaise: true, ct).ConfigureAwait(false); }
+            _tagsByName.TryGetValue(tagRef, out var def) &&
+            !string.IsNullOrWhiteSpace(def.ScanGroup) &&
+            // Case-insensitive lookup: scan group names come from human-typed config
+            // and the JSON DTO already lower-cases the lookup, so don't make ScanGroup
+            // values case-sensitive at runtime either.
+            TryGetCaseInsensitive(map, def.ScanGroup!, out var groupInterval))
+        {
+            return ApplyMinInterval(groupInterval);
+        }
+        return defaultInterval;
+    }
+
+    private static bool TryGetCaseInsensitive(IReadOnlyDictionary<string, TimeSpan> map, string key, out TimeSpan value)
+    {
+        if (map.TryGetValue(key, out value)) return true;
+        foreach (var kvp in map)
+            if (string.Equals(kvp.Key, key, StringComparison.OrdinalIgnoreCase))
+            {
+                value = kvp.Value;
+                return true;
+            }
+        value = default;
+        return false;
+    }
+
+    /// <summary>
+    ///     Test-only: count of distinct partition loops a subscription handle owns. Used by
+    ///     <c>S7ScanGroupPartitioningTests</c> to assert that 3 tags at 3 rates produce 3
+    ///     partitions (and 3 tags at 1 rate produce 1 partition).
+    /// </summary>
+    internal int GetPartitionCount(ISubscriptionHandle handle) =>
+        handle is S7SubscriptionHandle h && _subscriptions.TryGetValue(h.Id, out var state)
+            ? state.Partitions.Count
+            : 0;
+
+    /// <summary>
+    ///     Test-only: snapshot of the (interval, tag-count) pairs for a subscription's
+    ///     partitions. Surfaces the actual partitioning so tests can assert "5 tags split
+    ///     2 + 3" without grepping the poll-loop internals.
+    /// </summary>
+    internal IReadOnlyList<(TimeSpan Interval, int TagCount)> GetPartitionSummary(ISubscriptionHandle handle) =>
+        handle is S7SubscriptionHandle h && _subscriptions.TryGetValue(h.Id, out var state)
+            ? [.. state.Partitions.Select(p => (p.Interval, p.TagReferences.Count))]
+            : [];
+
+    private async Task PollLoopAsync(S7SubscriptionHandle handle, PartitionState part, CancellationToken ct)
+    {
+        // Initial-data push per OPC UA Part 4 convention. Each partition does its own
+        // initial push: the OPC UA stack receives one DataChange per tag at subscribe time
+        // regardless of which partition the tag landed in.
+        try { await PollOnceAsync(handle, part, forceRaise: true, ct).ConfigureAwait(false); }
         catch (OperationCanceledException) { return; }
         catch { /* first-read error — polling continues */ }
 
         while (!ct.IsCancellationRequested)
         {
-            try { await Task.Delay(state.Interval, ct).ConfigureAwait(false); }
+            try { await Task.Delay(part.Interval, ct).ConfigureAwait(false); }
             catch (OperationCanceledException) { return; }
 
-            try { await PollOnceAsync(state, forceRaise: false, ct).ConfigureAwait(false); }
+            try { await PollOnceAsync(handle, part, forceRaise: false, ct).ConfigureAwait(false); }
             catch (OperationCanceledException) { return; }
             catch { /* transient polling error — loop continues, health surface reflects it */ }
         }
     }
 
-    private async Task PollOnceAsync(SubscriptionState state, bool forceRaise, CancellationToken ct)
+    private async Task PollOnceAsync(S7SubscriptionHandle handle, PartitionState part, bool forceRaise, CancellationToken ct)
     {
-        var snapshots = await ReadAsync(state.TagReferences, ct).ConfigureAwait(false);
+        // ReadAsync takes _gate internally, which is what serialises every partition's
-        for (var i = 0; i < state.TagReferences.Count; i++)
+        // wire traffic against the single S7 connection. Multiple partitions racing for
+        // the gate is fine — short-running ones get serviced inside the long ones' Delay
+        // window, which is exactly the cadence-decoupling we want from PR-S7-C3.
+        var snapshots = await ReadAsync(part.TagReferences, ct).ConfigureAwait(false);
+        for (var i = 0; i < part.TagReferences.Count; i++)
         {
-            var tagRef = state.TagReferences[i];
+            var tagRef = part.TagReferences[i];
             var current = snapshots[i];
-            var lastSeen = state.LastValues.TryGetValue(tagRef, out var prev) ? prev : default;
+            var lastSeen = part.LastValues.TryGetValue(tagRef, out var prev) ? prev : default;
 
             if (forceRaise || !Equals(lastSeen?.Value, current.Value) || lastSeen?.StatusCode != current.StatusCode)
             {
-                state.LastValues[tagRef] = current;
+                part.LastValues[tagRef] = current;
-                OnDataChange?.Invoke(this, new DataChangeEventArgs(state.Handle, tagRef, current));
+                OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, tagRef, current));
             }
         }
     }
 
+    /// <summary>
+    ///     One subscription owns N partitions, one per distinct publishing interval.
+    ///     <see cref="TagReferences"/> is the original (unpartitioned) request preserved for
+    ///     diagnostics — runtime polling is driven by <see cref="Partitions"/>.
+    /// </summary>
     private sealed record SubscriptionState(
         S7SubscriptionHandle Handle,
+        IReadOnlyList<string> TagReferences,
+        TimeSpan DefaultInterval,
+        IReadOnlyList<PartitionState> Partitions);
+
+    /// <summary>
+    ///     One poll loop's worth of state: the tags it owns, its tick interval, its
+    ///     per-tag last-seen cache, and the CTS that <see cref="UnsubscribeAsync"/> /
+    ///     <see cref="DisposeAsync"/> trip.
+    /// </summary>
+    private sealed record PartitionState(
         IReadOnlyList<string> TagReferences,
         TimeSpan Interval,
         CancellationTokenSource Cts)

src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7DriverFactoryExtensions.cs

@@ -34,6 +34,22 @@ public static class S7DriverFactoryExtensions
             throw new InvalidOperationException(
                 $"S7 driver config for '{driverInstanceId}' missing required Host");
 
+        // PR-S7-C3 — translate ScanGroupIntervalsMs (string -> int ms) into the runtime
+        // string -> TimeSpan map. Skip any entry with a non-positive value rather than
+        // throwing, so a config typo (e.g. 0 ms) degrades to "fall back to default
+        // publishing interval" instead of breaking the whole driver init.
+        IReadOnlyDictionary<string, TimeSpan>? scanGroupMap = null;
+        if (dto.ScanGroupIntervalsMs is { Count: > 0 })
+        {
+            var built = new Dictionary<string, TimeSpan>(StringComparer.OrdinalIgnoreCase);
+            foreach (var kvp in dto.ScanGroupIntervalsMs)
+            {
+                if (string.IsNullOrWhiteSpace(kvp.Key) || kvp.Value <= 0) continue;
+                built[kvp.Key] = TimeSpan.FromMilliseconds(kvp.Value);
+            }
+            if (built.Count > 0) scanGroupMap = built;
+        }
+
         var options = new S7DriverOptions
         {
             Host = dto.Host!,
@@ -57,6 +73,7 @@ public static class S7DriverFactoryExtensions
                 fallback: TsapMode.Auto),
             LocalTsap = dto.LocalTsap,
             RemoteTsap = dto.RemoteTsap,
+            ScanGroupIntervals = scanGroupMap,
         };
 
         return new S7Driver(options, driverInstanceId);
@@ -72,7 +89,8 @@ public static class S7DriverFactoryExtensions
                 tagName: t.Name),
             Writable: t.Writable ?? true,
             StringLength: t.StringLength ?? 254,
-            WriteIdempotent: t.WriteIdempotent ?? false);
+            WriteIdempotent: t.WriteIdempotent ?? false,
+            ScanGroup: string.IsNullOrWhiteSpace(t.ScanGroup) ? null : t.ScanGroup);
 
     private static T ParseEnum<T>(string? raw, string driverInstanceId, string field,
         string? tagName = null, T? fallback = null) where T : struct, Enum
@@ -122,6 +140,15 @@ public static class S7DriverFactoryExtensions
 
         /// <summary>Optional 16-bit remote TSAP override. Required (with <see cref="LocalTsap"/>) when <c>TsapMode = Other</c>.</summary>
         public ushort? RemoteTsap { get; init; }
+
+        /// <summary>
+        ///     PR-S7-C3 — optional scan-group → publishing-interval (ms) map. Tags carrying
+        ///     a matching <see cref="S7TagDto.ScanGroup"/> string poll at the configured
+        ///     rate; tags with no group, or with a group not present here, fall back to
+        ///     the subscription default. Group names are matched case-insensitively. See
+        ///     <c>docs/v2/s7.md</c> "Per-tag scan groups" section.
+        /// </summary>
+        public Dictionary<string, int>? ScanGroupIntervalsMs { get; init; }
     }
 
     internal sealed class S7TagDto
@@ -132,6 +159,14 @@ public static class S7DriverFactoryExtensions
         public bool? Writable { get; init; }
         public int? StringLength { get; init; }
         public bool? WriteIdempotent { get; init; }
+
+        /// <summary>
+        ///     PR-S7-C3 — optional scan-group identifier. Resolved against
+        ///     <see cref="S7DriverConfigDto.ScanGroupIntervalsMs"/> at subscribe time.
+        ///     Null / empty = no group (legacy behaviour, falls back to subscription
+        ///     default publishing interval).
+        /// </summary>
+        public string? ScanGroup { get; init; }
     }
 
     internal sealed class S7ProbeDto

src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7DriverOptions.cs

@@ -122,6 +122,23 @@ public sealed class S7DriverOptions
     ///     non-<see cref="TsapMode.Auto"/> mode.
     /// </summary>
     public ushort? RemoteTsap { get; init; }
+
+    /// <summary>
+    ///     PR-S7-C3 — per-tag scan-group → publishing-interval map. When a tag declares a
+    ///     <see cref="S7TagDefinition.ScanGroup"/>, <see cref="S7Driver.SubscribeAsync"/>
+    ///     resolves its publishing rate by looking the group up in this dictionary; tags
+    ///     without a group, or with a group not present here, fall back to the
+    ///     subscription-default <c>publishingInterval</c> argument. Keys are matched
+    ///     case-insensitively. See <c>docs/v2/s7.md</c> "Per-tag scan groups" section.
+    /// </summary>
+    /// <remarks>
+    ///     The driver still owns one <c>Plc</c> connection serialized through the per-driver
+    ///     <c>_gate</c>, so partitioning into N poll loops does NOT parallelise wire-level
+    ///     reads — every partition queues against the same semaphore. Operator value is
+    ///     decoupling tick cadence: a 100 ms HMI tag isn't blocked behind a 10 s slow-poll
+    ///     batch any more, because the slow batch's <c>Task.Delay</c> isn't holding the gate.
+    /// </remarks>
+    public IReadOnlyDictionary<string, TimeSpan>? ScanGroupIntervals { get; init; }
 }
 
 /// <summary>
@@ -227,6 +244,15 @@ public sealed class S7ProbeOptions
 ///     they need bespoke layout handling and are tracked as a follow-up. Capped at 8000 to
 ///     keep the byte-range request inside a single S7 PDU envelope.
 /// </param>
+/// <param name="ScanGroup">
+///     PR-S7-C3 — optional scan-group identifier. When set, <c>SubscribeAsync</c> looks up
+///     the group's publishing interval in <see cref="S7DriverOptions.ScanGroupIntervals"/>
+///     and partitions the input tag list so all tags sharing that interval poll together
+///     in a dedicated background loop. Tags with no <c>ScanGroup</c>, or with a group not
+///     present in the map, fall back to the subscription's default publishing interval
+///     (legacy single-rate behaviour). Group names are matched case-insensitively. See
+///     <c>docs/v2/s7.md</c> "Per-tag scan groups" section.
+/// </param>
 public sealed record S7TagDefinition(
     string Name,
     string Address,
@@ -234,7 +260,8 @@ public sealed record S7TagDefinition(
     bool Writable = true,
     int StringLength = 254,
     bool WriteIdempotent = false,
-    int? ElementCount = null);
+    int? ElementCount = null,
+    string? ScanGroup = null);
 
 public enum S7DataType
 {

tests/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/S7_1500/S7_1500ScanGroupTests.cs

@@ -0,0 +1,96 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests.S7_1500;
+
+/// <summary>
+///     PR-S7-C3 — end-to-end coverage of per-tag scan-group partitioning. Subscribes three
+///     tags at three publishing intervals (100 ms / 1 s / 10 s) against the python-snap7
+///     S7-1500 fixture and asserts each gets its own tick stream with counts proportional
+///     to its rate. Scaffold only; runtime execution gated on the Snap7 fixture being up
+///     in CI.
+/// </summary>
+[Collection(Snap7ServerCollection.Name)]
+[Trait("Category", "Integration")]
+[Trait("Device", "S7_1500")]
+public sealed class S7_1500ScanGroupTests(Snap7ServerFixture sim)
+{
+    [Fact]
+    public async Task Driver_three_scan_groups_publish_independently()
+    {
+        if (sim.SkipReason is not null) Assert.Skip(sim.SkipReason);
+
+        // Reuse the smoke profile but override Tags + ScanGroupIntervals so each tag
+        // lands in its own group. The tags themselves are already seeded by the snap7
+        // fixture (DB1.DBW0, DB1.DBW10, DB1.DBD20 — same offsets the smoke tests use).
+        var baseOpts = S7_1500Profile.BuildOptions(sim.Host, sim.Port);
+        var options = new S7DriverOptions
+        {
+            Host = baseOpts.Host,
+            Port = baseOpts.Port,
+            CpuType = baseOpts.CpuType,
+            Rack = baseOpts.Rack,
+            Slot = baseOpts.Slot,
+            Timeout = baseOpts.Timeout,
+            Probe = baseOpts.Probe,
+            // Three groups, three rates. The 10s "Slow" group exercises the assertion that
+            // a slow batch's Task.Delay doesn't block faster partitions from polling — if
+            // the original (single-rate) implementation had been kept, every tag would
+            // tick at the slowest configured interval.
+            ScanGroupIntervals = new Dictionary<string, TimeSpan>(StringComparer.OrdinalIgnoreCase)
+            {
+                ["Fast"]   = TimeSpan.FromMilliseconds(100),
+                ["Medium"] = TimeSpan.FromSeconds(1),
+                ["Slow"]   = TimeSpan.FromSeconds(10),
+            },
+            Tags =
+            [
+                new S7TagDefinition("FastProbe",   "DB1.DBW0",  S7DataType.UInt16, ScanGroup: "Fast"),
+                new S7TagDefinition("MediumI16",   "DB1.DBW10", S7DataType.Int16,  ScanGroup: "Medium"),
+                new S7TagDefinition("SlowI32",     "DB1.DBD20", S7DataType.Int32,  ScanGroup: "Slow"),
+            ],
+        };
+
+        await using var drv = new S7Driver(options, driverInstanceId: "s7-scangroups");
+        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
+
+        // Per-tag tick counters. The OPC UA initial-data push fires once per tag at
+        // subscribe time regardless of partition (Part 4 contract), so we discount the
+        // first tick before evaluating the rate ratio.
+        var ticks = new System.Collections.Concurrent.ConcurrentDictionary<string, int>(StringComparer.OrdinalIgnoreCase);
+        drv.OnDataChange += (_, e) => ticks.AddOrUpdate(e.FullReference, 1, (_, n) => n + 1);
+
+        var handle = await drv.SubscribeAsync(
+            ["FastProbe", "MediumI16", "SlowI32"],
+            TimeSpan.FromSeconds(1),  // default; ignored because every tag carries a group
+            TestContext.Current.CancellationToken);
+
+        // Three groups → three partitions. This is the strongest claim of the PR: the
+        // driver split the input list into one poll loop per distinct interval.
+        drv.GetPartitionCount(handle).ShouldBe(3, "three distinct rates → three independent poll loops");
+
+        // Run for ~3 s and capture tick counts. With a 100 ms partition, ~30 ticks expected
+        // (minus the initial-data push, plus jitter). With a 1 s partition, ~3 ticks. With
+        // a 10 s partition, only the initial-data push fires inside the window.
+        await Task.Delay(TimeSpan.FromSeconds(3), TestContext.Current.CancellationToken);
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+
+        // Discount the initial-data push before checking ratios. After the discount, Fast
+        // must have produced strictly more ticks than Medium, and Medium must have
+        // produced at least one tick (Slow stays at 0 inside the 3-second window).
+        var fastSubsequent   = Math.Max(0, (ticks.GetValueOrDefault("FastProbe", 0)) - 1);
+        var mediumSubsequent = Math.Max(0, (ticks.GetValueOrDefault("MediumI16", 0)) - 1);
+
+        // Loose lower bound on Fast — wall-clock jitter on CI runners makes tighter bounds
+        // flaky. Anything above ~10 ticks in 3 s proves the 100 ms partition is actually
+        // running (i.e. it's not blocked behind the 10 s slow partition).
+        fastSubsequent.ShouldBeGreaterThan(10,
+            $"100 ms partition should fire many times in 3 s; observed Fast={fastSubsequent}, Medium={mediumSubsequent}");
+        // Strict ordering — the whole point of partitioning is that Fast > Medium even
+        // when Slow is sitting on a 10 s Task.Delay.
+        fastSubsequent.ShouldBeGreaterThan(mediumSubsequent,
+            "Fast partition (100 ms) must out-tick Medium partition (1 s) — partitions are independent");
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7ScanGroupPartitioningTests.cs

@@ -0,0 +1,320 @@
+using System.Reflection;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.S7.Tests;
+
+/// <summary>
+///     PR-S7-C3 — unit coverage for <see cref="S7Driver.SubscribeAsync"/> partitioning by
+///     resolved publishing interval. Each test wires a small tag map + scan-group rate map
+///     and asserts the driver spins up exactly the expected number of internal poll loops
+///     by inspecting the test-only <c>GetPartitionCount</c> / <c>GetPartitionSummary</c>
+///     entry points.
+/// </summary>
+/// <remarks>
+///     These tests don't initialise the driver (no live PLC) and don't drive ticks — they
+///     just verify the partitioning math at <c>SubscribeAsync</c> time. End-to-end tick
+///     cadence is covered by the integration smoke test
+///     <c>Driver_three_scan_groups_publish_independently</c>.
+/// </remarks>
+[Trait("Category", "Unit")]
+public sealed class S7ScanGroupPartitioningTests
+{
+    /// <summary>
+    ///     <see cref="S7Driver"/> resolves a tag's interval against its private
+    ///     <c>_tagsByName</c> dictionary, populated in <c>InitializeAsync</c>. The unit
+    ///     tests don't run init (no live PLC), so seed the dictionary directly via
+    ///     reflection. Mirrors the pattern in <c>S7DiscoveryAndSubscribeTests</c> which
+    ///     also exercises pre-init code paths.
+    /// </summary>
+    private static void SeedTagMap(S7Driver drv, params S7TagDefinition[] tags)
+    {
+        var field = typeof(S7Driver).GetField("_tagsByName", BindingFlags.NonPublic | BindingFlags.Instance);
+        field.ShouldNotBeNull();
+        var map = (Dictionary<string, S7TagDefinition>)field!.GetValue(drv)!;
+        foreach (var t in tags) map[t.Name] = t;
+    }
+
+    [Fact]
+    public async Task Three_distinct_intervals_produce_three_partitions()
+    {
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+            ScanGroupIntervals = new Dictionary<string, TimeSpan>(StringComparer.OrdinalIgnoreCase)
+            {
+                ["Fast"]   = TimeSpan.FromMilliseconds(100),
+                ["Medium"] = TimeSpan.FromSeconds(1),
+                ["Slow"]   = TimeSpan.FromSeconds(10),
+            },
+        };
+        using var drv = new S7Driver(opts, "s7-3rates");
+        SeedTagMap(drv,
+            new S7TagDefinition("FastTag",   "DB1.DBW0", S7DataType.Int16, ScanGroup: "Fast"),
+            new S7TagDefinition("MediumTag", "DB1.DBW2", S7DataType.Int16, ScanGroup: "Medium"),
+            new S7TagDefinition("SlowTag",   "DB1.DBW4", S7DataType.Int16, ScanGroup: "Slow"));
+
+        var handle = await drv.SubscribeAsync(
+            ["FastTag", "MediumTag", "SlowTag"],
+            TimeSpan.FromSeconds(1),
+            TestContext.Current.CancellationToken);
+
+        drv.GetPartitionCount(handle).ShouldBe(3, "3 distinct intervals → 3 separate poll loops");
+
+        var summary = drv.GetPartitionSummary(handle);
+        // Every partition owns exactly one tag — perfect 1:1 mapping.
+        summary.Count.ShouldBe(3);
+        summary.ShouldAllBe(p => p.TagCount == 1);
+        summary.Select(p => p.Interval).Order().ShouldBe(new[]
+        {
+            TimeSpan.FromMilliseconds(100),
+            TimeSpan.FromSeconds(1),
+            TimeSpan.FromSeconds(10),
+        });
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+    }
+
+    [Fact]
+    public async Task Same_interval_for_every_tag_collapses_to_one_partition()
+    {
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+            ScanGroupIntervals = new Dictionary<string, TimeSpan>(StringComparer.OrdinalIgnoreCase)
+            {
+                ["Default"] = TimeSpan.FromMilliseconds(500),
+            },
+        };
+        using var drv = new S7Driver(opts, "s7-1rate");
+        SeedTagMap(drv,
+            new S7TagDefinition("A", "DB1.DBW0", S7DataType.Int16, ScanGroup: "Default"),
+            new S7TagDefinition("B", "DB1.DBW2", S7DataType.Int16, ScanGroup: "Default"),
+            new S7TagDefinition("C", "DB1.DBW4", S7DataType.Int16, ScanGroup: "Default"));
+
+        var handle = await drv.SubscribeAsync(
+            ["A", "B", "C"],
+            TimeSpan.FromMilliseconds(500),
+            TestContext.Current.CancellationToken);
+
+        drv.GetPartitionCount(handle).ShouldBe(1, "all three tags share the same group → single poll loop");
+        drv.GetPartitionSummary(handle)[0].TagCount.ShouldBe(3);
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+    }
+
+    [Fact]
+    public async Task Mixed_two_at_100ms_and_three_at_1s_produces_two_partitions_with_correct_counts()
+    {
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+            ScanGroupIntervals = new Dictionary<string, TimeSpan>(StringComparer.OrdinalIgnoreCase)
+            {
+                ["Hmi"]  = TimeSpan.FromMilliseconds(100),
+                ["Slow"] = TimeSpan.FromSeconds(1),
+            },
+        };
+        using var drv = new S7Driver(opts, "s7-mixed");
+        SeedTagMap(drv,
+            new S7TagDefinition("Hmi1",  "DB1.DBW0",  S7DataType.Int16, ScanGroup: "Hmi"),
+            new S7TagDefinition("Hmi2",  "DB1.DBW2",  S7DataType.Int16, ScanGroup: "Hmi"),
+            new S7TagDefinition("Slow1", "DB1.DBW10", S7DataType.Int16, ScanGroup: "Slow"),
+            new S7TagDefinition("Slow2", "DB1.DBW12", S7DataType.Int16, ScanGroup: "Slow"),
+            new S7TagDefinition("Slow3", "DB1.DBW14", S7DataType.Int16, ScanGroup: "Slow"));
+
+        var handle = await drv.SubscribeAsync(
+            ["Hmi1", "Hmi2", "Slow1", "Slow2", "Slow3"],
+            TimeSpan.FromMilliseconds(500),
+            TestContext.Current.CancellationToken);
+
+        drv.GetPartitionCount(handle).ShouldBe(2);
+
+        var summary = drv.GetPartitionSummary(handle);
+        var fast = summary.Single(p => p.Interval == TimeSpan.FromMilliseconds(100));
+        var slow = summary.Single(p => p.Interval == TimeSpan.FromSeconds(1));
+        fast.TagCount.ShouldBe(2, "Hmi1 + Hmi2 share the 100 ms partition");
+        slow.TagCount.ShouldBe(3, "Slow1 + Slow2 + Slow3 share the 1 s partition");
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+    }
+
+    [Fact]
+    public async Task Tags_without_scan_group_fall_back_to_subscription_default_interval()
+    {
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+            // No ScanGroupIntervals map — every tag must resolve to the subscription default.
+        };
+        using var drv = new S7Driver(opts, "s7-no-groups");
+        SeedTagMap(drv,
+            new S7TagDefinition("Plain1", "DB1.DBW0", S7DataType.Int16),
+            new S7TagDefinition("Plain2", "DB1.DBW2", S7DataType.Int16));
+
+        var handle = await drv.SubscribeAsync(
+            ["Plain1", "Plain2"],
+            TimeSpan.FromMilliseconds(750),
+            TestContext.Current.CancellationToken);
+
+        drv.GetPartitionCount(handle).ShouldBe(1, "no groups configured → legacy single-partition behaviour");
+        drv.GetPartitionSummary(handle)[0].Interval.ShouldBe(TimeSpan.FromMilliseconds(750));
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+    }
+
+    [Fact]
+    public async Task Tag_with_unknown_scan_group_falls_back_to_subscription_default()
+    {
+        // Operator typo: tag declares "Fst" but the rate map has "Fast". The driver should
+        // NOT throw — instead the tag silently falls through to the subscription default,
+        // matching the "config typo degrades, doesn't break" stance from the factory layer.
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+            ScanGroupIntervals = new Dictionary<string, TimeSpan>(StringComparer.OrdinalIgnoreCase)
+            {
+                ["Fast"] = TimeSpan.FromMilliseconds(100),
+            },
+        };
+        using var drv = new S7Driver(opts, "s7-typo");
+        SeedTagMap(drv,
+            new S7TagDefinition("Typo", "DB1.DBW0", S7DataType.Int16, ScanGroup: "Fst"),
+            new S7TagDefinition("Real", "DB1.DBW2", S7DataType.Int16, ScanGroup: "Fast"));
+
+        var handle = await drv.SubscribeAsync(
+            ["Typo", "Real"],
+            TimeSpan.FromSeconds(2),
+            TestContext.Current.CancellationToken);
+
+        var summary = drv.GetPartitionSummary(handle);
+        summary.Count.ShouldBe(2);
+        summary.Single(p => p.Interval == TimeSpan.FromMilliseconds(100)).TagCount.ShouldBe(1);
+        summary.Single(p => p.Interval == TimeSpan.FromSeconds(2)).TagCount.ShouldBe(1);
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+    }
+
+    [Fact]
+    public async Task Scan_group_lookup_is_case_insensitive()
+    {
+        // The factory DTO already lower-cases keys — runtime lookup must follow suit so a
+        // tag declaring "FAST" still resolves against a rate-map key of "Fast".
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+            ScanGroupIntervals = new Dictionary<string, TimeSpan>(StringComparer.Ordinal)
+            {
+                ["Fast"] = TimeSpan.FromMilliseconds(100),
+            },
+        };
+        using var drv = new S7Driver(opts, "s7-caseins");
+        SeedTagMap(drv,
+            new S7TagDefinition("T", "DB1.DBW0", S7DataType.Int16, ScanGroup: "FAST"));
+
+        var handle = await drv.SubscribeAsync(
+            ["T"], TimeSpan.FromSeconds(2), TestContext.Current.CancellationToken);
+
+        drv.GetPartitionSummary(handle)[0].Interval.ShouldBe(TimeSpan.FromMilliseconds(100));
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+    }
+
+    [Fact]
+    public async Task Group_interval_below_100ms_is_floored_to_100ms()
+    {
+        // The 100 ms floor protects the S7 mailbox from sub-scan polling. It applies to
+        // BOTH the subscription default AND any per-group override — a mis-typed 50 ms
+        // group rate must NOT slip below the floor.
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+            ScanGroupIntervals = new Dictionary<string, TimeSpan>(StringComparer.OrdinalIgnoreCase)
+            {
+                ["TooFast"] = TimeSpan.FromMilliseconds(25),
+            },
+        };
+        using var drv = new S7Driver(opts, "s7-floor-group");
+        SeedTagMap(drv,
+            new S7TagDefinition("T", "DB1.DBW0", S7DataType.Int16, ScanGroup: "TooFast"));
+
+        var handle = await drv.SubscribeAsync(
+            ["T"], TimeSpan.FromSeconds(1), TestContext.Current.CancellationToken);
+
+        drv.GetPartitionSummary(handle)[0].Interval.ShouldBe(TimeSpan.FromMilliseconds(100));
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+    }
+
+    [Fact]
+    public async Task Unsubscribe_disposes_every_partition_engine()
+    {
+        // Every partition CTS must be cancelled + disposed so a multi-rate subscription
+        // doesn't leak background poll tasks on unsubscribe. Verified indirectly by the
+        // partition-count dropping to zero post-unsubscribe (the dictionary is purged) and
+        // by Dispose being safe to call again with no exception.
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+            ScanGroupIntervals = new Dictionary<string, TimeSpan>(StringComparer.OrdinalIgnoreCase)
+            {
+                ["A"] = TimeSpan.FromMilliseconds(100),
+                ["B"] = TimeSpan.FromMilliseconds(200),
+                ["C"] = TimeSpan.FromMilliseconds(500),
+            },
+        };
+        using var drv = new S7Driver(opts, "s7-cleanup");
+        SeedTagMap(drv,
+            new S7TagDefinition("Ta", "DB1.DBW0", S7DataType.Int16, ScanGroup: "A"),
+            new S7TagDefinition("Tb", "DB1.DBW2", S7DataType.Int16, ScanGroup: "B"),
+            new S7TagDefinition("Tc", "DB1.DBW4", S7DataType.Int16, ScanGroup: "C"));
+
+        var handle = await drv.SubscribeAsync(
+            ["Ta", "Tb", "Tc"],
+            TimeSpan.FromSeconds(1),
+            TestContext.Current.CancellationToken);
+
+        drv.GetPartitionCount(handle).ShouldBe(3);
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+
+        drv.GetPartitionCount(handle).ShouldBe(0, "post-unsubscribe the subscription is purged from the dictionary");
+        // Idempotent: a second unsubscribe must be a no-op, not throw.
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+    }
+
+    [Fact]
+    public async Task Legacy_single_rate_path_unchanged_when_no_tag_carries_a_scan_group()
+    {
+        // Sanity: existing deployments that don't set ScanGroup or ScanGroupIntervals must
+        // see exactly one partition with exactly the requested publishing interval — the
+        // PR is opt-in and zero-impact for legacy callers.
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+        };
+        using var drv = new S7Driver(opts, "s7-legacy");
+        SeedTagMap(drv,
+            new S7TagDefinition("L1", "DB1.DBW0", S7DataType.Int16),
+            new S7TagDefinition("L2", "DB1.DBW2", S7DataType.Int16));
+
+        var handle = await drv.SubscribeAsync(
+            ["L1", "L2"], TimeSpan.FromMilliseconds(250), TestContext.Current.CancellationToken);
+
+        drv.GetPartitionCount(handle).ShouldBe(1);
+        drv.GetPartitionSummary(handle)[0].Interval.ShouldBe(TimeSpan.FromMilliseconds(250));
+        drv.GetPartitionSummary(handle)[0].TagCount.ShouldBe(2);
+
+        await drv.UnsubscribeAsync(handle, TestContext.Current.CancellationToken);
+    }
+}