Fixed an MFM compliance issue when editing bitstream images

Author: Digitoxin1

DiskImageTool/Bitstream/BitstreamRegionSector.vb

@@ -9,15 +9,12 @@
             Public Property HasData As Boolean
             Public Property IDAMChecksumValid As Boolean
             Public Property Length As UInteger
+            Public Property Overlaps As Boolean
             Public Property SectorId As Byte
             Public Property SectorIndex As UShort
             Public Property Side As Byte
             Public Property StartIndex As UInteger
             Public Property Track As Byte
-            Public Overrides Function ToString() As String
-                'Return _SectorIndex & " (" & _SectorId & ")"
-                Return _SectorId
-            End Function
         End Class
     End Namespace
 End Namespace

DiskImageTool/Bitstream/IBM_MFM/IBM_MFM_Sector.vb

@@ -150,7 +150,7 @@
                 Return MFMCRC16(_IDArea)
             End Function
 
-            Public Function GetDataBitstream() As BitArray
+            Public Function GetDataBitstream(SeedBit As Boolean) As BitArray
                 Dim DataSize = GetSizeBytes()
                 Dim Buffer(DataSize + 2 - 1) As Byte
 
@@ -159,7 +159,7 @@
                 Offset += DataSize
                 Array.Copy(BitConverter.GetBytes(_DataChecksum), 0, Buffer, Offset, 2)
 
-                Return MFMEncodeBytes(Buffer, 1)
+                Return MFMEncodeBytes(Buffer, SeedBit)
             End Function
 
             Public Function GetSizeBytes() As UInteger
@@ -173,11 +173,22 @@
             Public Sub UpdateBitstream()
                 UpdateChecksum()
 
-                Dim Bitstream = GetDataBitstream()
+                Dim SeedBit = GetSeedBit(_DataOffset)
+
+                Dim Bitstream = GetDataBitstream(SeedBit)
 
                 For i = 0 To Bitstream.Length - 1
                     _Bitstream(_DataOffset + i) = Bitstream(i)
                 Next
+
+                Dim Offset = _DataOffset + Bitstream.Length - 1
+                If Offset < _Bitstream.Length - 2 Then
+                    Dim PrevDataBit = _Bitstream(Offset)
+                    Dim DataBit = _Bitstream(Offset + 2)
+                    Dim ClockBit = (Not DataBit And Not PrevDataBit)
+                    _Bitstream(Offset + 1) = ClockBit
+                End If
+
             End Sub
 
             Public Sub UpdateChecksum()
@@ -190,6 +201,13 @@
                 Return BitConverter.ToUInt16(Checksum, 0)
             End Function
 
+            Private Function GetSeedBit(Offset As UInteger) As Boolean
+                If Offset > 0 Then
+                    Return _Bitstream(Offset - 1)
+                Else
+                    Return True
+                End If
+            End Function
             Private Function ProcessDataField(BitStream As BitArray, Start As UInteger) As Integer
                 Dim MFMPattern = BytesToBits(MFM_Sync_Bytes)
 

DiskImageTool/Bitstream/IBM_MFM/IBM_MFM_Tools.vb

@@ -428,16 +428,17 @@
 
                         Dim SectorSize = DataLength
                         Dim SectorLength = (SectorEnd - BitstreamIndex) \ MFM_BYTE_SIZE
-                        Dim Overlaps As Boolean = False
 
                         If SectorSize > SectorLength Then
                             SectorSize = SectorLength
-                            Overlaps = True
+                            RegionSector.Overlaps = True
+                        Else
+                            RegionSector.Overlaps = False
                         End If
 
                         SyncNullCount = 0
                         GapCount = 0
-                        If Overlaps Then
+                        If RegionSector.Overlaps Then
                             Buffer = MFMGetBytes(Bitstream, BitstreamIndex, SectorSize)
                             SyncNullCount = GetByteCount(Buffer, 0, 0)
                             SectorSize -= SyncNullCount
@@ -464,7 +465,7 @@
                         ByteIndex += SectorSize
                         BitstreamIndex += SectorSize * MFM_BYTE_SIZE
 
-                        If Not Overlaps And SectorSize < SectorLength - 2 Then
+                        If Not RegionSector.Overlaps And SectorSize < SectorLength - 2 Then
                             RegionData.Regions.Add(New BitstreamRegion(RegionType, ByteIndex, MFM_CRC_SIZE, RegionSector, BitOffset))
                             ByteIndex += MFM_CRC_SIZE
                             BitstreamIndex += MFM_CRC_SIZE * MFM_BYTE_SIZE
@@ -655,22 +656,18 @@
             Public Function MFMEncodeBytes(Data() As Byte, SeedBit As Boolean) As BitArray
                 Dim Bitstream As New BitArray(Data.Length * 16)
                 Dim bitCount As Integer = 0
-                Dim dateBit As Boolean
+                Dim dataBit As Boolean
                 Dim clockBit As Boolean
 
                 Dim prevDataBit = SeedBit
                 For i = 0 To Data.Length - 1
                     For j = 7 To 0 Step -1
-                        dateBit = CBool((Data(i) And (1 << j)))
-                        If Not dateBit And Not prevDataBit Then
-                            clockBit = True
-                        Else
-                            clockBit = False
-                        End If
+                        dataBit = CBool((Data(i) And (1 << j)))
+                        clockBit = (Not dataBit And Not prevDataBit)
                         Bitstream.Set(bitCount, clockBit)
-                        Bitstream.Set(bitCount + 1, dateBit)
+                        Bitstream.Set(bitCount + 1, dataBit)
 
-                        prevDataBit = dateBit
+                        prevDataBit = dataBit
                         bitCount += 2
                     Next
                 Next

DiskImageTool/DiskImageTool.vbproj

@@ -30,7 +30,7 @@
     <TargetCulture>en-US</TargetCulture>
     <ProductName>DiskImageTool</ProductName>
     <PublisherName>Digitoxin</PublisherName>
-    <ApplicationRevision>0</ApplicationRevision>
+    <ApplicationRevision>1</ApplicationRevision>
     <ApplicationVersion>2.8.0.%2a</ApplicationVersion>
     <UseApplicationTrust>false</UseApplicationTrust>
     <PublishWizardCompleted>true</PublishWizardCompleted>

DiskImageTool/Forms/HexViewRawForm.vb

@@ -1300,14 +1300,17 @@ Public Class HexViewRawForm
             Dim Sector = _RegionData.Sectors(SectorIndex)
             TooltipText = "Sector Id: " & vbTab & vbTab & Sector.SectorId
             TooltipText &= vbCrLf & "Size: " & vbTab & vbTab & vbTab & Sector.DataLength
+
             If Sector.Track <> _Track Then
                 TooltipText &= vbCrLf & "Track: " & vbTab & vbTab & vbTab & Sector.Track
             End If
+
             If Sector.Side <> _Side Then
                 TooltipText &= vbCrLf & "Side: " & vbTab & vbTab & vbTab & Sector.Side
             End If
 
             TooltipText &= vbCrLf & "Address Checksum: " & vbTab & If(Sector.IDAMChecksumValid, "Valid", "Invalid")
+
             If Sector.HasData Then
                 TooltipText &= vbCrLf & "Data Checksum: " & vbTab & vbTab & If(Sector.DataChecksumValid, "Valid", "Invalid")
             End If
@@ -1323,6 +1326,10 @@ Public Class HexViewRawForm
                 DAMText = "Unknown"
             End If
             TooltipText &= vbCrLf & "Data Address Mark: " & vbTab & DAMText
+
+            If Sector.Overlaps Then
+                TooltipText &= vbCrLf & "Overlaps"
+            End If
         End If
 
         If TooltipText <> _ToolTip.GetToolTip(PanelSectors) Then

DiskImageTool/My Project/AssemblyInfo.vb

@@ -31,4 +31,4 @@ Imports System.Runtime.InteropServices
 ' <Assembly: AssemblyVersion("1.0.*")>
 
 <Assembly: AssemblyVersion("1.0.0.0")>
-<Assembly: AssemblyFileVersion("2.8.0.0")>
+<Assembly: AssemblyFileVersion("2.8.0.1")>