docs/Driver.AbLegacy.Cli.md

@@ -19,7 +19,8 @@ dotnet run --project src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Cli -- --help
 |---|---|---|
 | `-g` / `--gateway` | **required** | Canonical `ab://host[:port]/cip-path` |
 | `-P` / `--plc-type` | `Slc500` | Slc500 / MicroLogix / Plc5 / LogixPccc |
-| `--timeout-ms` | `5000` | Per-operation timeout |
+| `--timeout-ms` | `5000` | Per-operation timeout — see precedence note below |
+| `--retries` | `0` | Retry count on transient `BadCommunicationError` (PR 9 / #252) |
 | `--verbose` | off | Serilog debug output |
 
 Family ↔ CIP-path cheat sheet:
@@ -29,6 +30,31 @@ Family ↔ CIP-path cheat sheet:
 - **LogixPccc** — `1,0` (Logix controller accessed via the PCCC compatibility
   layer; rare)
 
+### Per-device timeout / retry tuning (#252, PR 9)
+
+The CLI's `--timeout-ms` is the **driver-wide default** when launched as a
+one-shot test client. In production (server-side, multi-device deployment)
+each `AbLegacyDeviceOptions` row carries its own optional `Timeout` /
+`Retries` that override the driver-wide value.
+
+Precedence (highest → lowest): per-device override → driver-wide default →
+hard-coded fallback (2000 ms / 0 retries).
+
+Tuning cheat sheet — start here, measure, then trim:
+
+| Family | Recommended `Timeout` | Notes |
+|---|---|---|
+| SLC 5/01 (RS-232 / DH+ bridge) | **5000 ms** | Slowest of the bunch; serial round-trip plus DH+ hop |
+| SLC 5/02 / 5/03 (DH+) | 3000 ms | Bridged Ethernet → DH+ adds ~1 s |
+| **SLC 5/04 / 5/05** (Ethernet) | **2000 ms** | Fastest of the SLC family — direct EIP/PCCC |
+| MicroLogix 1100 / 1400 | **3000 ms** | Single-CPU, slow scan; no backplane |
+| PLC-5 (Ethernet I/F) | 2500 ms | Comparable to SLC 5/05 over EIP |
+| LogixPccc compat layer | 2000 ms | Logix CPU is fast; PCCC layer is the floor |
+
+A small `--retries 1` (or `2` for slow chassis) is generally safe — the retry
+loop only fires on transient `BadCommunicationError`; terminal errors
+(`BadNodeIdUnknown`, `BadTypeMismatch`, …) surface on the first attempt.
+
 ## PCCC address primer
 
 File letters imply data type; type flag still required so the CLI knows how to

docs/drivers/AbLegacy-Test-Fixture.md

@@ -123,6 +123,33 @@ cover the common ones but uncommon ones (`R` counters, `S` status files,
    network; parts are end-of-life but still available. PLC-5 +
    LogixPccc-mode behaviour + DF1 serial need specific controllers.
 
+## Per-device options (`AbLegacyDeviceOptions`)
+
+Each entry in `AbLegacyDriverOptions.Devices` carries:
+
+| Field | Type | Default | Notes |
+|---|---|---|---|
+| `HostAddress` | string | required | `ab://host[:port]/cip-path` |
+| `PlcFamily` | enum | `Slc500` | Slc500 / MicroLogix / Plc5 / LogixPccc |
+| `DeviceName` | string | null | Friendly label used in browse + diagnostics |
+| `Timeout` | TimeSpan? | null → driver-wide default | **PR 9 / #252** — wins over the driver-wide `Timeout`. Mix-and-match: SLC 5/01 ≈ 5 s, SLC 5/05 ≈ 2 s, MicroLogix 1100 ≈ 3 s |
+| `Retries` | int? | null → driver-wide default → 0 | **PR 9 / #252** — retries on transient `BadCommunicationError`; terminal errors surface on the first attempt |
+
+JSON shape (mirrored on `AbLegacyDeviceDto`):
+
+```json
+{
+  "HostAddress": "ab://192.168.1.10/1,0",
+  "PlcFamily": "Slc500",
+  "DeviceName": "slc-5-01-line-A",
+  "TimeoutMs": 5000,
+  "Retries": 1
+}
+```
+
+Per-device overrides also flow into the probe loop — slow chassis won't be
+falsely marked Stopped just because the driver-wide probe timeout is tight.
+
 ## Key fixture / config files
 
 - `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyServerFixture.cs`

scripts/smoke/seed-ablegacy-smoke.sql

@@ -80,15 +80,23 @@ VALUES (@Gen, @EqId, @EqUuid, @DrvId, @LineId, 'slc-sim', 'ablegacy-001', 1);
 
 -- AB Legacy DriverInstance — SLC 500 target. Replace the placeholder gateway
 -- `192.168.1.10` with the real PLC / RSEmulate host before running.
+--
+-- PR 9 / #252 demo: the device row carries `"TimeoutMs": 500` + `"Retries": 1`,
+-- both overriding the driver-wide `TimeoutMs: 2000` / `Retries: 0` defaults.
+-- For real chassis tune per family (SLC 5/01 ≈ 5000, SLC 5/05 ≈ 2000,
+-- MicroLogix 1100 ≈ 3000); see docs/Driver.AbLegacy.Cli.md for the cheat sheet.
 INSERT dbo.DriverInstance(GenerationId, DriverInstanceId, ClusterId, NamespaceId,
                           Name, DriverType, DriverConfig, Enabled)
 VALUES (@Gen, @DrvId, @ClusterId, @NsId, 'ablegacy-smoke', 'AbLegacy', N'{
   "TimeoutMs": 2000,
+  "Retries": 0,
   "Devices": [
     {
       "HostAddress": "ab://127.0.0.1:44818/1,0",
       "PlcFamily": "Slc500",
-      "DeviceName": "slc-500"
+      "DeviceName": "slc-500",
+      "TimeoutMs": 500,
+      "Retries": 1
     }
   ],
   "Probe": { "Enabled": true, "IntervalMs": 5000, "TimeoutMs": 2000, "ProbeAddress": "S:0" },

src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs

@@ -209,6 +209,24 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
     internal DeviceState? GetDeviceState(string hostAddress) =>
         _devices.TryGetValue(hostAddress, out var s) ? s : null;
 
+    /// <summary>
+    ///     PR 9 — per-device timeout precedence: device-level override wins, otherwise the
+    ///     driver-wide default. Probe loop has its own timeout knob via
+    ///     <see cref="AbLegacyProbeOptions.Timeout"/> but still falls back to the per-device
+    ///     value when the probe override is absent (handled at the call site).
+    /// </summary>
+    internal TimeSpan ResolveTimeout(DeviceState device) =>
+        device.Options.Timeout ?? _options.Timeout;
+
+    /// <summary>
+    ///     PR 9 — per-device retry count: device-level override wins, otherwise the driver-wide
+    ///     default, otherwise zero (single attempt). The driver-wide default itself is
+    ///     <c>null</c> by default so a vanilla AbLegacy config still issues exactly one read per
+    ///     reference, matching pre-PR-9 behaviour.
+    /// </summary>
+    internal int ResolveRetries(DeviceState device) =>
+        device.Options.Retries ?? _options.Retries ?? 0;
+
     // ---- IReadable ----
 
     public async Task<IReadOnlyList<DataValueSnapshot>> ReadAsync(
@@ -232,57 +250,77 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
                 continue;
             }
 
-            try
+            // PR 9 — per-device retry loop: on transient BadCommunicationError (libplctag throw
+            // OR a non-zero status that maps to BadCommunicationError) retry up to N times. A
+            // terminal mapped status (e.g. BadNodeIdUnknown for a missing PLC tag, BadTypeMismatch
+            // for a decoder mismatch) is surfaced as-is — retrying won't fix it. Cancellation
+            // always rethrows.
+            var retries = ResolveRetries(device);
+            DataValueSnapshot? snapshot = null;
+            for (var attempt = 0; attempt <= retries; attempt++)
             {
-                var runtime = await EnsureTagRuntimeAsync(device, def, cancellationToken).ConfigureAwait(false);
-                await runtime.ReadAsync(cancellationToken).ConfigureAwait(false);
-
-                var status = runtime.GetStatus();
-                if (status != 0)
+                try
                 {
-                    results[i] = new DataValueSnapshot(null,
-                        AbLegacyStatusMapper.MapLibplctagStatus(status), null, now);
-                    _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
-                        $"libplctag status {status} reading {reference}");
-                    continue;
-                }
+                    var runtime = await EnsureTagRuntimeAsync(device, def, cancellationToken).ConfigureAwait(false);
+                    await runtime.ReadAsync(cancellationToken).ConfigureAwait(false);
 
-                var parsed = AbLegacyAddress.TryParse(def.Address, device.Options.PlcFamily);
-                // PR 7 — array contiguous block. Decode N consecutive elements via the runtime's
-                // per-index accessor and box the result as a typed .NET array. The parser has
-                // already rejected array+bit and array+sub-element combinations, so the array
-                // path can ignore the bit/sub-element decoders entirely.
-                int arrayCount;
-                if (parsed is not null && (def.ArrayLength is not null || (parsed.ArrayCount ?? 1) > 1))
-                {
-                    arrayCount = ResolveElementCount(def, parsed);
-                }
-                else arrayCount = 1;
+                    var status = runtime.GetStatus();
+                    if (status != 0)
+                    {
+                        var mappedStatus = AbLegacyStatusMapper.MapLibplctagStatus(status);
+                        // Transient: BadCommunicationError → eligible for retry.
+                        if (mappedStatus == AbLegacyStatusMapper.BadCommunicationError && attempt < retries)
+                        {
+                            continue;
+                        }
+                        snapshot = new DataValueSnapshot(null, mappedStatus, null, now);
+                        _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
+                            $"libplctag status {status} reading {reference}");
+                        break;
+                    }
 
-                if (arrayCount > 1)
-                {
-                    var arr = DecodeArrayAs(runtime, def.DataType, arrayCount);
-                    results[i] = new DataValueSnapshot(arr, AbLegacyStatusMapper.Good, now, now);
+                    var parsed = AbLegacyAddress.TryParse(def.Address, device.Options.PlcFamily);
+                    // PR 7 — array contiguous block. Decode N consecutive elements via the runtime's
+                    // per-index accessor and box the result as a typed .NET array. The parser has
+                    // already rejected array+bit and array+sub-element combinations, so the array
+                    // path can ignore the bit/sub-element decoders entirely.
+                    int arrayCount;
+                    if (parsed is not null && (def.ArrayLength is not null || (parsed.ArrayCount ?? 1) > 1))
+                    {
+                        arrayCount = ResolveElementCount(def, parsed);
+                    }
+                    else arrayCount = 1;
+
+                    if (arrayCount > 1)
+                    {
+                        var arr = DecodeArrayAs(runtime, def.DataType, arrayCount);
+                        snapshot = new DataValueSnapshot(arr, AbLegacyStatusMapper.Good, now, now);
+                        _health = new DriverHealth(DriverState.Healthy, now, null);
+                        break;
+                    }
+
+                    // Timer/Counter/Control status bits route through GetBit at the parent-word
+                    // address — translate the .DN/.EN/etc. sub-element to its standard bit position
+                    // and pass it down to the runtime as a synthetic bitIndex.
+                    var decodeBit = parsed?.BitIndex
+                        ?? AbLegacyDataTypeExtensions.StatusBitIndex(def.DataType, parsed?.SubElement);
+                    var value = runtime.DecodeValue(def.DataType, decodeBit);
+                    snapshot = new DataValueSnapshot(value, AbLegacyStatusMapper.Good, now, now);
                     _health = new DriverHealth(DriverState.Healthy, now, null);
-                    continue;
+                    break;
+                }
+                catch (OperationCanceledException) { throw; }
+                catch (Exception ex)
+                {
+                    // Transient — exhaust retries before reporting BadCommunicationError.
+                    if (attempt < retries) continue;
+                    snapshot = new DataValueSnapshot(null,
+                        AbLegacyStatusMapper.BadCommunicationError, null, now);
+                    _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
                 }
-
-                // Timer/Counter/Control status bits route through GetBit at the parent-word
-                // address — translate the .DN/.EN/etc. sub-element to its standard bit position
-                // and pass it down to the runtime as a synthetic bitIndex.
-                var decodeBit = parsed?.BitIndex
-                    ?? AbLegacyDataTypeExtensions.StatusBitIndex(def.DataType, parsed?.SubElement);
-                var value = runtime.DecodeValue(def.DataType, decodeBit);
-                results[i] = new DataValueSnapshot(value, AbLegacyStatusMapper.Good, now, now);
-                _health = new DriverHealth(DriverState.Healthy, now, null);
-            }
-            catch (OperationCanceledException) { throw; }
-            catch (Exception ex)
-            {
-                results[i] = new DataValueSnapshot(null,
-                    AbLegacyStatusMapper.BadCommunicationError, null, now);
-                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
             }
+            results[i] = snapshot ?? new DataValueSnapshot(null,
+                AbLegacyStatusMapper.BadCommunicationError, null, now);
         }
 
         return results;
@@ -441,13 +479,17 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
 
     private async Task ProbeLoopAsync(DeviceState state, CancellationToken ct)
     {
+        // PR 9 — per-device timeout wins over the probe's own timeout. Slow chassis (SLC 5/01
+        // RS-232 ~5 s round-trip) need their per-device override to flow into the probe too,
+        // otherwise the probe times out before the device ever has a chance to respond.
+        var probeTimeout = state.Options.Timeout ?? _options.Probe.Timeout;
         var probeParams = new AbLegacyTagCreateParams(
             Gateway: state.ParsedAddress.Gateway,
             Port: state.ParsedAddress.Port,
             CipPath: state.ParsedAddress.CipPath,
             LibplctagPlcAttribute: state.Profile.LibplctagPlcAttribute,
             TagName: _options.Probe.ProbeAddress!,
-            Timeout: _options.Probe.Timeout);
+            Timeout: probeTimeout);
 
         IAbLegacyTagRuntime? probeRuntime = null;
         while (!ct.IsCancellationRequested)
@@ -553,7 +595,7 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
             CipPath: device.ParsedAddress.CipPath,
             LibplctagPlcAttribute: device.Profile.LibplctagPlcAttribute,
             TagName: parentName,
-            Timeout: _options.Timeout));
+            Timeout: ResolveTimeout(device)));
         try
         {
             await runtime.InitializeAsync(ct).ConfigureAwait(false);
@@ -601,7 +643,7 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
             CipPath: device.ParsedAddress.CipPath,
             LibplctagPlcAttribute: device.Profile.LibplctagPlcAttribute,
             TagName: tagName,
-            Timeout: _options.Timeout,
+            Timeout: ResolveTimeout(device),
             ElementCount: elementCount));
         try
         {

src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriverFactoryExtensions.cs

@@ -38,7 +38,10 @@ public static class AbLegacyDriverFactoryExtensions
                         $"AB Legacy config for '{driverInstanceId}' has a device missing HostAddress"),
                     PlcFamily: ParseEnum<AbLegacyPlcFamily>(d.PlcFamily, driverInstanceId, "PlcFamily",
                         fallback: AbLegacyPlcFamily.Slc500),
-                    DeviceName: d.DeviceName))]
+                    DeviceName: d.DeviceName,
+                    // PR 9 — per-device timeout / retry overrides. Device-level wins over driver-wide.
+                    Timeout: d.TimeoutMs is int devMs ? TimeSpan.FromMilliseconds(devMs) : null,
+                    Retries: d.Retries))]
                 : [],
             Tags = dto.Tags is { Count: > 0 }
                 ? [.. dto.Tags.Select(t => new AbLegacyTagDefinition(
@@ -64,6 +67,9 @@ public static class AbLegacyDriverFactoryExtensions
                 ProbeAddress = dto.Probe?.ProbeAddress ?? "S:0",
             },
             Timeout = TimeSpan.FromMilliseconds(dto.TimeoutMs ?? 2_000),
+            // PR 9 — driver-wide retry default. null ≡ 0 retries (single attempt). Per-device
+            // Retries on AbLegacyDeviceOptions still wins.
+            Retries = dto.Retries,
         };
 
         return new AbLegacyDriver(options, driverInstanceId);
@@ -95,6 +101,12 @@ public static class AbLegacyDriverFactoryExtensions
     internal sealed class AbLegacyDriverConfigDto
     {
         public int? TimeoutMs { get; init; }
+        /// <summary>
+        ///     PR 9 — driver-wide retry count for transient <c>BadCommunicationError</c> reads.
+        ///     <c>null</c> ≡ <c>0</c> (single attempt). A per-device override on
+        ///     <see cref="AbLegacyDeviceDto.Retries"/> wins.
+        /// </summary>
+        public int? Retries { get; init; }
         public List<AbLegacyDeviceDto>? Devices { get; init; }
         public List<AbLegacyTagDto>? Tags { get; init; }
         public AbLegacyProbeDto? Probe { get; init; }
@@ -105,6 +117,20 @@ public static class AbLegacyDriverFactoryExtensions
         public string? HostAddress { get; init; }
         public string? PlcFamily { get; init; }
         public string? DeviceName { get; init; }
+
+        /// <summary>
+        ///     PR 9 — optional per-device timeout in ms. Wins over the driver-wide
+        ///     <see cref="AbLegacyDriverConfigDto.TimeoutMs"/>. Tune this per chassis: SLC 5/01
+        ///     RS-232 ≈ 5000, SLC 5/05 ≈ 2000, MicroLogix 1100 ≈ 3000.
+        /// </summary>
+        public int? TimeoutMs { get; init; }
+
+        /// <summary>
+        ///     PR 9 — optional per-device retry count for transient <c>BadCommunicationError</c>
+        ///     reads. Wins over the driver-wide <see cref="AbLegacyDriverConfigDto.Retries"/>.
+        ///     <c>null</c> at both levels = single attempt.
+        /// </summary>
+        public int? Retries { get; init; }
     }
 
     internal sealed class AbLegacyTagDto

src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriverOptions.cs

@@ -13,13 +13,35 @@ public sealed class AbLegacyDriverOptions
     public IReadOnlyList<AbLegacyDeviceOptions> Devices { get; init; } = [];
     public IReadOnlyList<AbLegacyTagDefinition> Tags { get; init; } = [];
     public AbLegacyProbeOptions Probe { get; init; } = new();
+
+    /// <summary>
+    ///     Driver-wide default per-operation timeout. Applies to every device unless that device
+    ///     overrides it via <see cref="AbLegacyDeviceOptions.Timeout"/> (PR 9).
+    /// </summary>
     public TimeSpan Timeout { get; init; } = TimeSpan.FromSeconds(2);
+
+    /// <summary>
+    ///     PR 9 — driver-wide default retry count for transient
+    ///     <c>BadCommunicationError</c> reads. <c>null</c> ≡ <c>0</c> (single attempt). Applies
+    ///     to every device unless that device overrides it via
+    ///     <see cref="AbLegacyDeviceOptions.Retries"/>.
+    /// </summary>
+    public int? Retries { get; init; }
 }
 
+/// <summary>
+///     Per-device options for the AB Legacy driver. PR 9 added optional <see cref="Timeout"/>
+///     and <see cref="Retries"/> overrides — chassis families have very different per-operation
+///     latency floors (SLC 5/01 RS-232 ~5 s; SLC 5/05 ~2 s; ML1100 ~3 s) so a single driver-wide
+///     timeout always misfires on at least one device. Both fields are optional and fall back
+///     to the driver-wide default on <see cref="AbLegacyDriverOptions"/>.
+/// </summary>
 public sealed record AbLegacyDeviceOptions(
     string HostAddress,
     AbLegacyPlcFamily PlcFamily = AbLegacyPlcFamily.Slc500,
-    string? DeviceName = null);
+    string? DeviceName = null,
+    TimeSpan? Timeout = null,
+    int? Retries = null);
 
 /// <summary>
 ///     One PCCC-backed OPC UA variable. <c>Address</c> is the canonical PCCC file-address

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyPerDeviceTimeoutTests.cs

@@ -0,0 +1,68 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.PlcFamilies;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests;
+
+/// <summary>
+///     PR 9 — per-device timeout integration scaffold. Build-only at PR 9 time: the ab_server
+///     PCCC simulator answers in &lt;100 ms locally so a 500 ms per-device timeout doesn't
+///     normally trip. Either an <c>iptables --delay</c> sidecar or a <c>tc qdisc</c> netem
+///     filter must be wired up first; until then the test asserts that a <i>generous</i>
+///     per-device timeout still completes successfully (the precedence path itself is
+///     exercised), with the slow-path failure case expressed in unit tests via
+///     <see cref="FakeAbLegacyTag"/>.
+/// </summary>
+[Collection(AbLegacyServerCollection.Name)]
+[Trait("Category", "Integration")]
+[Trait("Simulator", "ab_server-PCCC")]
+public sealed class AbLegacyPerDeviceTimeoutTests(AbLegacyServerFixture sim)
+{
+    [AbLegacyFact]
+    public async Task Per_device_Timeout_override_flows_into_runtime_against_ab_server()
+    {
+        if (sim.SkipReason is not null) Assert.Skip(sim.SkipReason);
+
+        var deviceUri = $"ab://{sim.Host}:{sim.Port}/{sim.CipPath}";
+        await using var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            // Driver-wide tight 500 ms; per-device override gives the simulator 5 s headroom
+            // to demonstrate the precedence rule in a wire-level setting.
+            Timeout = TimeSpan.FromMilliseconds(500),
+            Devices = [new AbLegacyDeviceOptions(
+                deviceUri,
+                AbLegacyPlcFamily.Slc500,
+                Timeout: TimeSpan.FromSeconds(5))],
+            Tags = [new AbLegacyTagDefinition(
+                Name: "IntCounter",
+                DeviceHostAddress: deviceUri,
+                Address: "N7:0",
+                DataType: AbLegacyDataType.Int)],
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, driverInstanceId: "ablegacy-pr9-timeout");
+
+        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
+        var snapshots = await drv.ReadAsync(["IntCounter"], TestContext.Current.CancellationToken);
+
+        // Per-device override picked up; the read against the simulator succeeds because the
+        // 5 s per-device cap supersedes the otherwise-too-tight 500 ms driver-wide default.
+        snapshots.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good);
+    }
+
+    /// <summary>
+    ///     Skeleton for the inverse — slow-link (<c>tc qdisc</c> / <c>iptables --delay</c>) +
+    ///     tight per-device timeout. Skipped pending the netem sidecar work tracked in
+    ///     <see href="../Docker/README.md#per-device-timeout-fixture">Docker/README.md</see>.
+    /// </summary>
+    [AbLegacyFact(Skip = "Pending netem / iptables-delay sidecar — see Docker/README.md")]
+    public Task Per_device_Timeout_below_simulated_delay_surfaces_BadCommunicationError()
+    {
+        // Future shape:
+        //   docker compose --profile slc500-slow up -d   (adds netem qdisc on the egress)
+        //   override Timeout: TimeSpan.FromMilliseconds(100)
+        //   ReadAsync ⇒ snapshots.Single().StatusCode == BadCommunicationError
+        //   while a sibling device (no override → 5 s) keeps reading Good.
+        return Task.CompletedTask;
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/README.md

@@ -139,6 +139,38 @@ bit writes to real hardware or RSEmulate 500 until upstream resolves.
 See [`docs/drivers/AbLegacy-Test-Fixture.md`](../../../docs/drivers/AbLegacy-Test-Fixture.md)
 for the full coverage map.
 
+## Per-device timeout fixture (PR 9 / #252) — TODO
+
+`AbLegacyPerDeviceTimeoutTests.Per_device_Timeout_below_simulated_delay_surfaces_BadCommunicationError`
+needs a slow-link sidecar before it can run for real. The simulator answers
+in <100 ms locally, so a 500 ms per-device timeout never trips against
+the unmodified container.
+
+Two options, neither wired up at PR 9 time:
+
+1. **`tc qdisc` netem inside the container** — add to `docker-compose.yml`:
+
+   ```yaml
+   # services:
+   #   ablegacy-slc500-slow:
+   #     extends: ablegacy-slc500
+   #     cap_add: [NET_ADMIN]
+   #     command: >
+   #       sh -c "tc qdisc add dev eth0 root netem delay 800ms &&
+   #              ab_server --plc=SLC500 --port=44818 --path=1,0 --tag=N7[200]:INT16"
+   ```
+
+   `--cap-add=NET_ADMIN` is required because `tc qdisc` mutates the
+   container's egress queue. Combine with `AB_LEGACY_COMPOSE_PROFILE=slc500-slow`
+   to point the suite at the slow profile.
+
+2. **`iptables --delay` shim** — sidecar container that NATs port 44818 and
+   adds a fixed delay on the SYN/ACK + payload path. More portable than
+   netem (no `NET_ADMIN` on the simulator itself) but adds a hop.
+
+When either lands, drop the `Skip = …` on the integration test and assert
+the precedence rule end-to-end.
+
 ## References
 
 - [libplctag on GitHub](https://github.com/libplctag/libplctag) — `ab_server`

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyPerDeviceTimeoutTests.cs

@@ -0,0 +1,283 @@
+using System.Text.Json;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy;
+using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.PlcFamilies;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests;
+
+/// <summary>
+///     PR 9 — per-device <c>Timeout</c> + <c>Retries</c> overrides. SLC 5/01 needs ~5 s,
+///     SLC 5/05 ~2 s, MicroLogix 1100 ~3 s — a single driver-wide timeout always misfires on
+///     at least one chassis. Verifies the precedence rules (device > driver-wide > default),
+///     that the resolved timeout flows into <see cref="AbLegacyTagCreateParams.Timeout"/>, and
+///     that the retry loop honours the per-device count.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class AbLegacyPerDeviceTimeoutTests
+{
+    private const string Host = "ab://10.0.0.5/1,0";
+
+    [Fact]
+    public async Task Per_device_Timeout_flows_into_AbLegacyTagCreateParams()
+    {
+        var factory = new FakeAbLegacyTagFactory();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            // Driver-wide default 2 s — the device override below should win.
+            Timeout = TimeSpan.FromSeconds(2),
+            Devices =
+            [
+                new AbLegacyDeviceOptions(Host, AbLegacyPlcFamily.Slc500,
+                    DeviceName: "slc-501",
+                    Timeout: TimeSpan.FromSeconds(5)),
+            ],
+            Tags = [new AbLegacyTagDefinition("X", Host, "N7:0", AbLegacyDataType.Int)],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+
+        factory.Tags["N7:0"].CreationParams.Timeout.ShouldBe(TimeSpan.FromSeconds(5));
+    }
+
+    [Fact]
+    public async Task Absent_per_device_Timeout_falls_back_to_driver_wide()
+    {
+        var factory = new FakeAbLegacyTagFactory();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Timeout = TimeSpan.FromSeconds(7),
+            Devices = [new AbLegacyDeviceOptions(Host, AbLegacyPlcFamily.Slc500)],
+            Tags = [new AbLegacyTagDefinition("X", Host, "N7:0", AbLegacyDataType.Int)],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+
+        factory.Tags["N7:0"].CreationParams.Timeout.ShouldBe(TimeSpan.FromSeconds(7));
+    }
+
+    [Fact]
+    public async Task Two_devices_each_use_their_own_Timeout_override()
+    {
+        const string fastHost = "ab://10.0.0.5/1,0";
+        const string slowHost = "ab://10.0.0.6/";
+        var factory = new FakeAbLegacyTagFactory();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Timeout = TimeSpan.FromSeconds(2),
+            Devices =
+            [
+                new AbLegacyDeviceOptions(fastHost, AbLegacyPlcFamily.Slc500,
+                    Timeout: TimeSpan.FromMilliseconds(500)),
+                new AbLegacyDeviceOptions(slowHost, AbLegacyPlcFamily.MicroLogix,
+                    Timeout: TimeSpan.FromSeconds(5)),
+            ],
+            Tags =
+            [
+                new AbLegacyTagDefinition("Fast", fastHost, "N7:0", AbLegacyDataType.Int),
+                new AbLegacyTagDefinition("Slow", slowHost, "N7:1", AbLegacyDataType.Int),
+            ],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(["Fast", "Slow"], CancellationToken.None);
+
+        factory.Tags["N7:0"].CreationParams.Timeout.ShouldBe(TimeSpan.FromMilliseconds(500));
+        factory.Tags["N7:1"].CreationParams.Timeout.ShouldBe(TimeSpan.FromSeconds(5));
+    }
+
+    [Fact]
+    public async Task Per_device_Retries_2_yields_3_attempts_before_failure()
+    {
+        var factory = new FakeAbLegacyTagFactory();
+        factory.Customise = p => new FakeAbLegacyTag(p)
+        {
+            ThrowOnRead = true,
+            Exception = new TimeoutException("simulated transient"),
+        };
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices =
+            [
+                new AbLegacyDeviceOptions(Host, AbLegacyPlcFamily.Slc500, Retries: 2),
+            ],
+            Tags = [new AbLegacyTagDefinition("X", Host, "N7:0", AbLegacyDataType.Int)],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+
+        snapshots.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.BadCommunicationError);
+        // 1 initial + 2 retries = 3 attempts.
+        factory.Tags["N7:0"].ReadCount.ShouldBe(3);
+    }
+
+    [Fact]
+    public async Task No_Retries_yields_single_attempt()
+    {
+        var factory = new FakeAbLegacyTagFactory();
+        factory.Customise = p => new FakeAbLegacyTag(p)
+        {
+            ThrowOnRead = true,
+            Exception = new TimeoutException("simulated transient"),
+        };
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            // Both null — defaults to 0 retries (single attempt).
+            Devices = [new AbLegacyDeviceOptions(Host, AbLegacyPlcFamily.Slc500)],
+            Tags = [new AbLegacyTagDefinition("X", Host, "N7:0", AbLegacyDataType.Int)],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+
+        factory.Tags["N7:0"].ReadCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Driver_wide_Retries_applies_when_device_omits_override()
+    {
+        var factory = new FakeAbLegacyTagFactory();
+        factory.Customise = p => new FakeAbLegacyTag(p)
+        {
+            ThrowOnRead = true,
+            Exception = new TimeoutException("simulated transient"),
+        };
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Retries = 1, // driver-wide → 2 attempts total
+            Devices = [new AbLegacyDeviceOptions(Host, AbLegacyPlcFamily.Slc500)],
+            Tags = [new AbLegacyTagDefinition("X", Host, "N7:0", AbLegacyDataType.Int)],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+
+        factory.Tags["N7:0"].ReadCount.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task Per_device_Retries_overrides_driver_wide_default()
+    {
+        var factory = new FakeAbLegacyTagFactory();
+        factory.Customise = p => new FakeAbLegacyTag(p)
+        {
+            ThrowOnRead = true,
+            Exception = new TimeoutException("simulated transient"),
+        };
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Retries = 5, // driver-wide
+            // Per-device says zero retries — should win, single attempt.
+            Devices = [new AbLegacyDeviceOptions(Host, AbLegacyPlcFamily.Slc500, Retries: 0)],
+            Tags = [new AbLegacyTagDefinition("X", Host, "N7:0", AbLegacyDataType.Int)],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+
+        factory.Tags["N7:0"].ReadCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Successful_read_after_one_transient_does_not_burn_remaining_retries()
+    {
+        // Verifies retries stop once the call succeeds — we shouldn't keep hammering.
+        var factory = new FakeAbLegacyTagFactory();
+        var attemptsBeforeSuccess = 1;
+        factory.Customise = p =>
+        {
+            var fake = new FlappyFake(p)
+            {
+                FailFirstN = attemptsBeforeSuccess,
+                FinalValue = 42,
+            };
+            return fake;
+        };
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions(Host, AbLegacyPlcFamily.Slc500, Retries: 3)],
+            Tags = [new AbLegacyTagDefinition("X", Host, "N7:0", AbLegacyDataType.Int)],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+
+        snapshots.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good);
+        snapshots.Single().Value.ShouldBe(42);
+        // 1 throw + 1 success = 2 attempts (we should NOT use all 4).
+        factory.Tags["N7:0"].ReadCount.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task Dto_round_trip_preserves_TimeoutMs_and_Retries_at_both_levels()
+    {
+        const string json = """
+            {
+              "TimeoutMs": 4000,
+              "Retries": 1,
+              "Devices": [
+                {
+                  "HostAddress": "ab://10.0.0.5/1,0",
+                  "PlcFamily": "Slc500",
+                  "TimeoutMs": 5000,
+                  "Retries": 2
+                }
+              ],
+              "Probe": { "Enabled": false },
+              "Tags": [
+                { "Name": "X", "DeviceHostAddress": "ab://10.0.0.5/1,0", "Address": "N7:0", "DataType": "Int" }
+              ]
+            }
+            """;
+
+        // Use the static factory so we exercise the deserialisation path used in production.
+        var drv = AbLegacyDriverFactoryExtensions.CreateInstance("drv-roundtrip", json);
+        await drv.InitializeAsync(json, CancellationToken.None);
+
+        var state = drv.GetDeviceState("ab://10.0.0.5/1,0").ShouldNotBeNull();
+
+        state.Options.Timeout.ShouldBe(TimeSpan.FromMilliseconds(5000));
+        state.Options.Retries.ShouldBe(2);
+
+        // Per-device override wins over driver-wide.
+        drv.ResolveRetries(state).ShouldBe(2);
+        drv.ResolveTimeout(state).ShouldBe(TimeSpan.FromMilliseconds(5000));
+
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    /// <summary>
+    ///     A fake that throws the first <c>FailFirstN</c> reads then succeeds. Used to assert
+    ///     the retry loop stops once a call succeeds — it should not exhaust the retry budget.
+    /// </summary>
+    private sealed class FlappyFake : FakeAbLegacyTag
+    {
+        public int FailFirstN { get; set; }
+        public object? FinalValue { get; set; }
+        private int _calls;
+        public FlappyFake(AbLegacyTagCreateParams p) : base(p) { }
+
+        public override Task ReadAsync(CancellationToken ct)
+        {
+            _calls++;
+            // Increment ReadCount via the base accessor (it does its own increment + throw
+            // bookkeeping). Toggle ThrowOnRead based on the call number so the base helper does
+            // the throw for us.
+            if (_calls <= FailFirstN)
+            {
+                ThrowOnRead = true;
+                Exception = new TimeoutException("flap");
+            }
+            else
+            {
+                ThrowOnRead = false;
+                Value = FinalValue;
+            }
+            return base.ReadAsync(ct);
+        }
+    }
+}