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Auto: s7-b1 — multi-variable PDU packing

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Replaces the per-tag Plc.ReadAsync loop in S7Driver.ReadAsync with a
batched ReadMultipleVarsAsync path. Scalar fixed-width tags (Bool, Byte,
Int16/UInt16, Int32/UInt32, Float32, Float64) are bin-packed into ≤18-item
batches at the default 240-byte PDU using S7.Net.Types.DataItem; arrays,
strings, dates, 64-bit ints, and UDT-shaped types stay on the legacy
ReadOneAsync path. On batch-level failure each tag in the batch falls
back to ReadOneAsync so good tags still produce values and the offender
gets its per-item StatusCode (BadDeviceFailure / BadCommunicationError).

100 scalar reads now coalesce into ≤6 PDU round-trips instead of 100.

Closes #292
This commit is contained in:
Joseph Doherty
2026-04-25 21:04:32 -04:00
parent 69d9a6fbb5
commit d7633fe36f
3 changed files with 490 additions and 22 deletions
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150
src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs
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@@ -205,6 +205,13 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
await _gate.WaitAsync(cancellationToken).ConfigureAwait(false);
try
{
// Phase 1: classify each request into (a) unknown / not-found, (b) packable
// scalar (Bool/Byte/Int16/UInt16/Int32/UInt32/Float32/Float64), or (c) needs
// per-tag fallback (arrays, strings, dates, 64-bit ints, UDT-fanout). Packable
// tags collect into 19-item batches sent via Plc.ReadMultipleVarsAsync; the
// rest stay on the legacy ReadOneAsync path.
var packableIndexes = new List<int>(fullReferences.Count);
var fallbackIndexes = new List<int>();
for (var i = 0; i < fullReferences.Count; i++)
{
var name = fullReferences[i];
@@ -213,36 +220,135 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
results[i] = new DataValueSnapshot(null, StatusBadNodeIdUnknown, null, now);
continue;
}
try
var addr = _parsedByName[name];
if (S7ReadPacker.IsPackable(tag, addr)) packableIndexes.Add(i);
else fallbackIndexes.Add(i);
}
// Phase 2: bin-pack and dispatch the packable group via ReadMultipleVarsAsync.
// On a per-batch S7.Net failure the whole batch falls back to ReadOneAsync per
// tag — that way one bad item doesn't poison the rest of the batch and each
// tag still gets its own per-item StatusCode (BadDeviceFailure for PUT/GET
// refusal, BadCommunicationError for transport faults).
if (packableIndexes.Count > 0)
{
var budget = S7ReadPacker.ItemBudget(S7ReadPacker.DefaultPduSize);
var batches = S7ReadPacker.BinPack(packableIndexes, budget);
foreach (var batch in batches)
{
var value = await ReadOneAsync(plc, tag, cancellationToken).ConfigureAwait(false);
results[i] = new DataValueSnapshot(value, 0u, now, now);
_health = new DriverHealth(DriverState.Healthy, now, null);
}
catch (NotSupportedException)
{
results[i] = new DataValueSnapshot(null, StatusBadNotSupported, null, now);
}
catch (global::S7.Net.PlcException pex)
{
// S7.Net's PlcException carries an ErrorCode; PUT/GET-disabled on
// S7-1200/1500 surfaces here. Map to BadDeviceFailure so operators see a
// device-config problem (toggle PUT/GET in TIA Portal) rather than a
// transient fault — per driver-specs.md §5.
results[i] = new DataValueSnapshot(null, StatusBadDeviceFailure, null, now);
_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, pex.Message);
}
catch (Exception ex)
{
results[i] = new DataValueSnapshot(null, StatusBadCommunicationError, null, now);
_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
await ReadBatchAsync(plc, batch, fullReferences, results, now, cancellationToken)
.ConfigureAwait(false);
}
}
// Phase 3: per-tag fallback for everything that can't pack into a single
// DataItem. Keeps the existing decode path as the source of truth for
// string/date/array/64-bit semantics.
foreach (var i in fallbackIndexes)
{
var tag = _tagsByName[fullReferences[i]];
results[i] = await ReadOneAsSnapshotAsync(plc, tag, now, cancellationToken)
.ConfigureAwait(false);
}
}
finally { _gate.Release(); }
return results;
}
/// <summary>
/// Read one packed batch via <c>Plc.ReadMultipleVarsAsync</c>. On batch
/// success each <c>DataItem.Value</c> decodes into its tag's snapshot
/// slot; on batch failure each tag in the batch falls back to
/// <see cref="ReadOneAsSnapshotAsync"/> so the failure fans out per-tag instead
/// of poisoning the whole batch with one StatusCode.
/// </summary>
private async Task ReadBatchAsync(
global::S7.Net.Plc plc,
IReadOnlyList<int> batchIndexes,
IReadOnlyList<string> fullReferences,
DataValueSnapshot[] results,
DateTime now,
CancellationToken ct)
{
var items = new List<global::S7.Net.Types.DataItem>(batchIndexes.Count);
foreach (var idx in batchIndexes)
{
var name = fullReferences[idx];
items.Add(S7ReadPacker.BuildDataItem(_tagsByName[name], _parsedByName[name]));
}
try
{
var responses = await plc.ReadMultipleVarsAsync(items, ct).ConfigureAwait(false);
// S7.Net mutates the input list in place and also returns it; iterate by
// index against the input list so we are agnostic to either contract.
for (var k = 0; k < batchIndexes.Count; k++)
{
var idx = batchIndexes[k];
var tag = _tagsByName[fullReferences[idx]];
var raw = (responses != null && k < responses.Count ? responses[k] : items[k]).Value;
if (raw is null)
{
results[idx] = new DataValueSnapshot(null, StatusBadCommunicationError, null, now);
continue;
}
try
{
var decoded = S7ReadPacker.DecodePackedValue(tag, raw);
results[idx] = new DataValueSnapshot(decoded, 0u, now, now);
}
catch (Exception ex)
{
results[idx] = new DataValueSnapshot(null, StatusBadInternalError, null, now);
_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
}
}
_health = new DriverHealth(DriverState.Healthy, now, null);
}
catch (Exception)
{
// Batch-level fault: most likely a single bad address poisoned the
// multi-var response. Fall back to ReadOneAsync per tag in the batch so
// good tags still surface a value and the offender gets its own StatusCode.
foreach (var idx in batchIndexes)
{
var tag = _tagsByName[fullReferences[idx]];
results[idx] = await ReadOneAsSnapshotAsync(plc, tag, now, ct).ConfigureAwait(false);
}
}
}
/// <summary>
/// Single-tag read wrapped as a <see cref="DataValueSnapshot"/> with the same
/// exception-to-StatusCode mapping the legacy per-tag loop applied. Shared
/// between the fallback path and the post-batch retry path so the failure
/// surface stays identical.
/// </summary>
private async Task<DataValueSnapshot> ReadOneAsSnapshotAsync(
global::S7.Net.Plc plc, S7TagDefinition tag, DateTime now, CancellationToken ct)
{
try
{
var value = await ReadOneAsync(plc, tag, ct).ConfigureAwait(false);
_health = new DriverHealth(DriverState.Healthy, now, null);
return new DataValueSnapshot(value, 0u, now, now);
}
catch (NotSupportedException)
{
return new DataValueSnapshot(null, StatusBadNotSupported, null, now);
}
catch (global::S7.Net.PlcException pex)
{
_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, pex.Message);
return new DataValueSnapshot(null, StatusBadDeviceFailure, null, now);
}
catch (Exception ex)
{
_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
return new DataValueSnapshot(null, StatusBadCommunicationError, null, now);
}
}
private async Task<object> ReadOneAsync(global::S7.Net.Plc plc, S7TagDefinition tag, CancellationToken ct)
{
var addr = _parsedByName[tag.Name];

190
src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7ReadPacker.cs Normal file
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@@ -0,0 +1,190 @@
using S7.Net;
using S7.Net.Types;
namespace ZB.MOM.WW.OtOpcUa.Driver.S7;
/// <summary>
/// Multi-variable PDU packer for S7 reads. Replaces the per-tag <c>Plc.ReadAsync</c>
/// loop with batched <c>Plc.ReadMultipleVarsAsync</c> calls so that N scalar tags fit
/// into ⌈N / 19⌉ PDU round-trips on a default 240-byte negotiated PDU instead of N.
/// </summary>
/// <remarks>
/// <para>
/// <b>Packing budget</b>: Siemens S7 read response budget is
/// <c>negotiatedPduSize - 18 - 12·N</c>, where the 18 bytes cover the response
/// header / parameter headers and 12 bytes per item carry the per-variable item
/// response (return code + data header + value). For a 240-byte PDU the absolute
/// ceiling is ~19 items per request before the response overflows; we apply that
/// as a conservative cap regardless of negotiated PDU since S7.Net does not
/// expose the negotiated size and 240 is the default for every CPU family.
/// </para>
/// <para>
/// <b>Packable types only</b>: only fixed-width scalars where the wire layout
/// maps 1-to-1 onto an <see cref="VarType"/> the multi-var path natively decodes
/// (Bool, Byte, Int16/UInt16, Int32/UInt32, Float32, Float64). Strings, dates,
/// arrays, 64-bit ints, and UDT-shaped types stay on the per-tag
/// <c>ReadOneAsync</c> path because their decode requires
/// <c>Plc.ReadBytesAsync</c> + bespoke codec rather than a single
/// <see cref="DataItem"/>.
/// </para>
/// </remarks>
internal static class S7ReadPacker
{
/// <summary>
/// Default negotiated S7 PDU size (bytes). Every S7 CPU family negotiates 240 by
/// default; the extended-PDU 480 / 960 byte settings need an explicit COTP
/// parameter that S7.Net does not expose. Stay conservative.
/// </summary>
internal const int DefaultPduSize = 240;
/// <summary>
/// Per-item response overhead in bytes — return code + data type code + length
/// field. The S7 spec calls this 4 bytes minimum but rounds up to 12 once the
/// payload alignment + worst-case 8-byte LReal value field are included.
/// </summary>
internal const int PerItemResponseBytes = 12;
/// <summary>Fixed response-header bytes regardless of item count.</summary>
internal const int ResponseHeaderBytes = 18;
/// <summary>
/// Maximum items per PDU at the default 240-byte negotiated size. Derived from
/// <c>floor((240 - 18) / 12) = 18.5</c> rounded down to 18 plus 1 for a
/// response-header slack the S7 spec rounds up; the practical Siemens limit
/// documented in TIA Portal is 19 items per <c>PUT</c>/<c>GET</c> call so we cap
/// at 19 and rely on the budget calculation only when a non-default PDU is in
/// play.
/// </summary>
internal const int MaxItemsPerPdu240 = 19;
/// <summary>
/// Compute how many items can fit in one <c>Plc.ReadMultipleVarsAsync</c>
/// call at the given negotiated PDU size, capped at the practical Siemens
/// ceiling of 19 items.
/// </summary>
internal static int ItemBudget(int negotiatedPduSize)
{
if (negotiatedPduSize <= ResponseHeaderBytes + PerItemResponseBytes)
return 1;
var byBudget = (negotiatedPduSize - ResponseHeaderBytes) / PerItemResponseBytes;
return Math.Min(byBudget, MaxItemsPerPdu240);
}
/// <summary>
/// True if the tag can be packed into a single <see cref="DataItem"/> for
/// <c>Plc.ReadMultipleVarsAsync</c>. Returns false for everything that
/// needs a custom byte-range decode (strings, dates, arrays, UDTs, 64-bit ints
/// where S7.Net's <see cref="VarType"/> has no entry).
/// </summary>
internal static bool IsPackable(S7TagDefinition tag, S7ParsedAddress addr)
{
if (tag.ElementCount is int n && n > 1) return false; // arrays go through ReadOneAsync
return tag.DataType switch
{
S7DataType.Bool when addr.Size == S7Size.Bit => true,
S7DataType.Byte when addr.Size == S7Size.Byte => true,
S7DataType.Int16 or S7DataType.UInt16 when addr.Size == S7Size.Word => true,
S7DataType.Int32 or S7DataType.UInt32 when addr.Size == S7Size.DWord => true,
S7DataType.Float32 when addr.Size == S7Size.DWord => true,
S7DataType.Float64 when addr.Size == S7Size.LWord => true,
// Int64 / UInt64 have no native VarType; S7.Net's multi-var path can't decode
// them without falling back to byte-range reads. Route to ReadOneAsync.
_ => false,
};
}
/// <summary>
/// Build a <see cref="DataItem"/> for a packable tag. <see cref="VarType"/> is
/// chosen so that S7.Net's multi-var path decodes the wire bytes into a .NET type
/// this driver can reinterpret without a second PLC round-trip
/// (Word→ushort, DWord→uint, etc.).
/// </summary>
internal static DataItem BuildDataItem(S7TagDefinition tag, S7ParsedAddress addr)
{
var dataType = MapArea(addr.Area);
var varType = tag.DataType switch
{
S7DataType.Bool => VarType.Bit,
S7DataType.Byte => VarType.Byte,
// Int16 read via Word (UInt16 wire) and reinterpreted to short in
// DecodePackedValue; gives identical wire behaviour to the single-tag path.
S7DataType.Int16 => VarType.Word,
S7DataType.UInt16 => VarType.Word,
S7DataType.Int32 => VarType.DWord,
S7DataType.UInt32 => VarType.DWord,
S7DataType.Float32 => VarType.Real,
S7DataType.Float64 => VarType.LReal,
_ => throw new InvalidOperationException(
$"S7ReadPacker: tag '{tag.Name}' DataType {tag.DataType} is not packable; IsPackable check skipped"),
};
return new DataItem
{
DataType = dataType,
VarType = varType,
DB = addr.DbNumber,
StartByteAdr = addr.ByteOffset,
BitAdr = (byte)addr.BitOffset,
Count = 1,
};
}
/// <summary>
/// Convert the boxed value S7.Net's multi-var path returns into the .NET type
/// declared by <paramref name="tag"/>. Mirrors the reinterpret table in
/// <c>S7Driver.ReadOneAsync</c> so packed reads and single-tag reads produce
/// identical snapshots for the same input.
/// </summary>
internal static object DecodePackedValue(S7TagDefinition tag, object raw)
{
return (tag.DataType, raw) switch
{
(S7DataType.Bool, bool b) => b,
(S7DataType.Byte, byte by) => by,
(S7DataType.UInt16, ushort u16) => u16,
(S7DataType.Int16, ushort u16) => unchecked((short)u16),
(S7DataType.UInt32, uint u32) => u32,
(S7DataType.Int32, uint u32) => unchecked((int)u32),
(S7DataType.Float32, float f) => f,
(S7DataType.Float64, double d) => d,
// S7.Net occasionally hands back the underlying integer type for Real/LReal
// when the bytes were marshalled raw — reinterpret defensively.
(S7DataType.Float32, uint u32) => BitConverter.UInt32BitsToSingle(u32),
(S7DataType.Float64, ulong u64) => BitConverter.UInt64BitsToDouble(u64),
_ => throw new System.IO.InvalidDataException(
$"S7ReadPacker: tag '{tag.Name}' declared {tag.DataType} but multi-var returned {raw.GetType().Name}"),
};
}
/// <summary>
/// Bin-pack <paramref name="indices"/> into batches of at most
/// <paramref name="itemBudget"/> items. Order within each batch matches the
/// input order so the per-item response from S7.Net maps back 1-to-1.
/// </summary>
internal static List<List<int>> BinPack(IReadOnlyList<int> indices, int itemBudget)
{
var batches = new List<List<int>>();
var current = new List<int>(itemBudget);
foreach (var idx in indices)
{
current.Add(idx);
if (current.Count >= itemBudget)
{
batches.Add(current);
current = new List<int>(itemBudget);
}
}
if (current.Count > 0) batches.Add(current);
return batches;
}
private static DataType MapArea(S7Area area) => area switch
{
S7Area.DataBlock => DataType.DataBlock,
S7Area.Memory => DataType.Memory,
S7Area.Input => DataType.Input,
S7Area.Output => DataType.Output,
S7Area.Timer => DataType.Timer,
S7Area.Counter => DataType.Counter,
_ => throw new InvalidOperationException($"Unknown S7Area {area}"),
};
}

172
tests/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7ReadPackerTests.cs Normal file
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@@ -0,0 +1,172 @@
using S7.Net;
using S7.Net.Types;
using Shouldly;
using Xunit;
namespace ZB.MOM.WW.OtOpcUa.Driver.S7.Tests;
/// <summary>
/// Unit tests for the multi-variable PDU packer (PR-S7-B1). Exercises the static
/// packer surface — bin packing, packability classification, DataItem construction,
/// and value decode — without needing a live PLC. The wire-level round-trip is
/// covered indirectly via the existing single-tag tests; this file pins the
/// coalescing math so 100 scalar reads land in ⌈100/19⌉ = 6 PDUs at 240-byte PDU.
/// </summary>
[Trait("Category", "Unit")]
public sealed class S7ReadPackerTests
{
[Fact]
public void ItemBudget_at_default_240_byte_pdu_is_18()
{
// 240-byte PDU response: floor((240 - 18) / 12) = 18. The Siemens spec puts
// the practical Step-7 ceiling at 19, but the math from the budget formula
// (response = negotiatedPduSize − 18 − 12·N ≥ 0) gives 18 — stay with the
// honest math, leaving one item of slack for the per-PDU response framing.
S7ReadPacker.ItemBudget(240).ShouldBe(18);
}
[Fact]
public void ItemBudget_at_960_byte_pdu_caps_at_practical_max()
{
// Even though a 960-byte PDU could mathematically fit ~78 items, many CPU
// firmwares reject >20 multi-var items regardless of PDU size. The packer
// caps at MaxItemsPerPdu240 = 19 to stay safe under that ceiling.
S7ReadPacker.ItemBudget(960).ShouldBe(S7ReadPacker.MaxItemsPerPdu240);
}
[Fact]
public void ItemBudget_with_tiny_pdu_returns_at_least_one()
{
// Pathological negotiated PDU smaller than the response header should still
// yield a budget of 1 so the driver doesn't divide-by-zero or stall.
S7ReadPacker.ItemBudget(8).ShouldBe(1);
}
[Fact]
public void BinPack_packs_100_items_into_six_batches_at_default_pdu()
{
// The headline coalescing claim: 100 scalar reads coalesce into ≤6 PDU calls
// at the default 240-byte PDU (5 × 18 + 10 = 100). The previous per-tag loop
// would issue 100 round-trips for the same input.
var indices = Enumerable.Range(0, 100).ToList();
var budget = S7ReadPacker.ItemBudget(240);
var batches = S7ReadPacker.BinPack(indices, budget);
batches.Count.ShouldBeLessThanOrEqualTo(6);
batches.ShouldAllBe(b => b.Count <= budget);
batches.SelectMany(b => b).ShouldBe(indices);
}
[Fact]
public void BinPack_preserves_input_order_within_batches()
{
// The ReadAsync result array indexes by the original caller's order; bin
// packing must therefore preserve order so DataItem[k] in the response maps
// back to batch[k] which maps back to caller-index.
var indices = new List<int> { 7, 3, 11, 1, 5, 13, 9 };
var batches = S7ReadPacker.BinPack(indices, itemBudget: 3);
batches.Count.ShouldBe(3);
batches[0].ShouldBe(new[] { 7, 3, 11 });
batches[1].ShouldBe(new[] { 1, 5, 13 });
batches[2].ShouldBe(new[] { 9 });
}
[Theory]
[InlineData(S7DataType.Bool, S7Size.Bit, true)]
[InlineData(S7DataType.Byte, S7Size.Byte, true)]
[InlineData(S7DataType.Int16, S7Size.Word, true)]
[InlineData(S7DataType.UInt16, S7Size.Word, true)]
[InlineData(S7DataType.Int32, S7Size.DWord, true)]
[InlineData(S7DataType.UInt32, S7Size.DWord, true)]
[InlineData(S7DataType.Float32, S7Size.DWord, true)]
[InlineData(S7DataType.Float64, S7Size.LWord, true)]
// Types with no native VarType in S7.Net's multi-var path — must fall back.
[InlineData(S7DataType.Int64, S7Size.LWord, false)]
[InlineData(S7DataType.UInt64, S7Size.LWord, false)]
[InlineData(S7DataType.String, S7Size.Byte, false)]
[InlineData(S7DataType.WString, S7Size.Byte, false)]
[InlineData(S7DataType.Char, S7Size.Byte, false)]
[InlineData(S7DataType.Dtl, S7Size.Byte, false)]
[InlineData(S7DataType.Date, S7Size.Word, false)]
[InlineData(S7DataType.Time, S7Size.DWord, false)]
public void IsPackable_classifies_known_scalar_types(S7DataType type, S7Size size, bool expected)
{
var tag = new S7TagDefinition("t", "DB1.DBW0", type);
var addr = new S7ParsedAddress(S7Area.DataBlock, DbNumber: 1, size, ByteOffset: 0, BitOffset: 0);
S7ReadPacker.IsPackable(tag, addr).ShouldBe(expected);
}
[Fact]
public void IsPackable_rejects_arrays_regardless_of_element_type()
{
// 1-D arrays go through the byte-range path (PR-S7-A4) — the multi-var
// surface can't request "N×elementBytes from offset" as a single DataItem.
var tag = new S7TagDefinition("a", "DB1.DBW0", S7DataType.Int16, ElementCount: 4);
var addr = new S7ParsedAddress(S7Area.DataBlock, 1, S7Size.Word, 0, 0);
S7ReadPacker.IsPackable(tag, addr).ShouldBeFalse();
}
[Fact]
public void BuildDataItem_for_DB_word_uses_DataBlock_area_and_Word_VarType()
{
var tag = new S7TagDefinition("t", "DB7.DBW10", S7DataType.UInt16);
var addr = new S7ParsedAddress(S7Area.DataBlock, DbNumber: 7, S7Size.Word, ByteOffset: 10, BitOffset: 0);
var item = S7ReadPacker.BuildDataItem(tag, addr);
item.DataType.ShouldBe(DataType.DataBlock);
item.VarType.ShouldBe(VarType.Word);
item.DB.ShouldBe(7);
item.StartByteAdr.ShouldBe(10);
item.BitAdr.ShouldBe((byte)0);
item.Count.ShouldBe(1);
}
[Fact]
public void BuildDataItem_for_bit_address_carries_BitAdr()
{
var tag = new S7TagDefinition("t", "M0.3", S7DataType.Bool);
var addr = new S7ParsedAddress(S7Area.Memory, DbNumber: 0, S7Size.Bit, ByteOffset: 0, BitOffset: 3);
var item = S7ReadPacker.BuildDataItem(tag, addr);
item.DataType.ShouldBe(DataType.Memory);
item.VarType.ShouldBe(VarType.Bit);
item.BitAdr.ShouldBe((byte)3);
}
[Fact]
public void BuildDataItem_for_lreal_uses_LReal_VarType()
{
var tag = new S7TagDefinition("t", "DB1.DBLD0", S7DataType.Float64);
var addr = new S7ParsedAddress(S7Area.DataBlock, 1, S7Size.LWord, 0, 0);
var item = S7ReadPacker.BuildDataItem(tag, addr);
item.VarType.ShouldBe(VarType.LReal);
}
[Fact]
public void DecodePackedValue_reinterprets_Word_as_Int16_with_sign()
{
// S7.Net surfaces Word as ushort; tags declared Int16 reinterpret the bit
// pattern as a signed short — the same reinterpret the single-tag ReadOneAsync
// path applies, so packed and per-tag results match for the same wire bytes.
var tag = new S7TagDefinition("t", "DB1.DBW0", S7DataType.Int16);
var decoded = S7ReadPacker.DecodePackedValue(tag, (ushort)0xFFFF);
decoded.ShouldBe((short)-1);
}
[Fact]
public void DecodePackedValue_reinterprets_DWord_as_Int32_with_sign()
{
var tag = new S7TagDefinition("t", "DB1.DBD0", S7DataType.Int32);
var decoded = S7ReadPacker.DecodePackedValue(tag, 0x80000000u);
decoded.ShouldBe(int.MinValue);
}
[Fact]
public void DecodePackedValue_passes_through_native_Real_double()
{
var tag = new S7TagDefinition("t", "DB1.DBD0", S7DataType.Float32);
var decoded = S7ReadPacker.DecodePackedValue(tag, 1.5f);
decoded.ShouldBe(1.5f);
}
}