Package com.webcodepro.applecommander.storage.physical

Class NibbleCodec

java.lang.Object

com.webcodepro.applecommander.storage.physical.NibbleCodec

public class NibbleCodec
extends Object

Field Summary

Fields

Modifier and Type	Field	Description
static final int[]	DOS32_ADDRESS_PROLOGUE
static final int[]	DOS32_DATA_PROLOGUE
static final int[]	DOS33_ADDRESS_PROLOGUE
static final int[]	DOS33_DATA_PROLOGUE

Constructor Summary

Constructors

Constructor	Description
NibbleCodec()

Method Summary

Modifier and Type	Method	Description
static int	decodeOddEven(byte[] buffer, int offset)	Decode odd-even bytes as stored on disk.
static void	encodeOddEven(byte[] buffer, int offset, int value)	Encode odd-even bytes to be stored on disk.
static int	identifySectorsPerTrack(byte[] trackData)	Identify if this is a 13-sector or 16-sector disk.
static int	locateField(int[] prologue, byte[] trackData, byte[] fieldData, int startingOffset)	Locate a field on the track.
static byte[]	readSectorFromTrack53(byte[] trackData, int track, int physicalSector, int sectorsPerTrack)	Locate physical sector in the given track data.
static byte[]	readSectorFromTrack62(byte[] trackData, int track, int physicalSector, int sectorsPerTrack)	Locate physical sector in the given track data.
static void	writeSectorToTrack(byte[] trackData, byte[] sectorData, int track, int physicalSector, int sectorsPerTrack)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

DOS32_ADDRESS_PROLOGUE

public static final int[] DOS32_ADDRESS_PROLOGUE

DOS32_DATA_PROLOGUE

public static final int[] DOS32_DATA_PROLOGUE

DOS33_ADDRESS_PROLOGUE

public static final int[] DOS33_ADDRESS_PROLOGUE

DOS33_DATA_PROLOGUE

public static final int[] DOS33_DATA_PROLOGUE

Constructor Details

NibbleCodec

public NibbleCodec()

Method Details

decodeOddEven

public static int decodeOddEven(byte[] buffer,
 int offset)

Decode odd-even bytes as stored on disk. The format will be in two bytes. They are stored as such:

     XX = 1d1d1d1d (odd data bits)
     YY = 1d1d1d1d (even data bits)
 

XX is then shifted by a bit and ANDed with YY to get the data byte. See page 3-12 in Beneath Apple DOS for more information.

encodeOddEven

public static void encodeOddEven(byte[] buffer,
 int offset,
 int value)

Encode odd-even bytes to be stored on disk. See decodeOddEven for the format.

See Also:

• decodeOddEven(byte[], int)

identifySectorsPerTrack

public static int identifySectorsPerTrack(byte[] trackData)

Identify if this is a 13-sector or 16-sector disk. Note that it is "guaranteed" to return 13, 16, or an exception.

readSectorFromTrack62

public static byte[] readSectorFromTrack62(byte[] trackData,
 int track,
 int physicalSector,
 int sectorsPerTrack)

Locate physical sector in the given track data. Decodes 6+2 encoding.

readSectorFromTrack53

public static byte[] readSectorFromTrack53(byte[] trackData,
 int track,
 int physicalSector,
 int sectorsPerTrack)

Locate physical sector in the given track data. Decodes 5+3 encoding.

locateField

public static int locateField(int[] prologue,
 byte[] trackData,
 byte[] fieldData,
 int startingOffset)

Locate a field on the track. These are identified by a 3 byte unique signature. Because of the way in which disk bytes are captured, we need to wrap around the track to ensure all sequences of bytes are accounted for.

This method fills fieldData as well as returning the last position referenced in the track buffer.

writeSectorToTrack

public static void writeSectorToTrack(byte[] trackData,
 byte[] sectorData,
 int track,
 int physicalSector,
 int sectorsPerTrack)