private static IEnumerable <WritePackage> CreateWritePackages(SiemensPlcProtocolContext s7Context, IEnumerable <WriteItem> vars) { var result = new List <WritePackage>(); foreach (var item in vars.OrderByDescending(x => x.NumberOfItems).ToList()) { var currentPackage = result.FirstOrDefault(package => package.TryAdd(item)); if (currentPackage == null) { if (item.NumberOfItems > s7Context.WriteItemMaxLength) { var bytesToWrite = item.NumberOfItems; ushort processed = 0; while (bytesToWrite > 0) { var slice = Math.Min(s7Context.WriteItemMaxLength, bytesToWrite); var child = WriteItem.CreateChild(item, (ushort)(item.Offset + processed), slice); if (slice < s7Context.WriteItemMaxLength) { currentPackage = result.FirstOrDefault(package => package.TryAdd(child)); } if (currentPackage == null) { currentPackage = new WritePackage(s7Context.PduSize); if (currentPackage.TryAdd(child)) { if (currentPackage.Full) { yield return(currentPackage.Return()); if (currentPackage.Handled) { currentPackage = null; } } else { result.Add(currentPackage); } } else { ThrowHelper.ThrowCouldNotAddPackageException(nameof(WritePackage)); } } processed += slice; bytesToWrite -= slice; } } else { currentPackage = new WritePackage(s7Context.PduSize); result.Add(currentPackage); if (!currentPackage.TryAdd(item)) { ThrowHelper.ThrowCouldNotAddPackageException(nameof(WritePackage)); } } } if (currentPackage != null) { if (currentPackage.Full) { yield return(currentPackage.Return()); } if (currentPackage.Handled) { result.Remove(currentPackage); } } } foreach (var package in result) { yield return(package.Return()); } }