Difference between revisions of "Tape\Disk Preservation"

From The Dragon Archive
Jump to: navigation, search
(VDK File Format)
m (File Formats)
Line 132: Line 132:
|9          ||Number of sides
|9          ||Number of sides
=== DMK File Format ===

Revision as of 09:02, 9 December 2009

(Community info on how to preserve existing tape and disk software - conversion from native Dragon to PC formats - WAV, CAS, VDK, DMK, conversion between formats and restoration back to physical media)


Tape to CAS File

Current preferred method is a special version of XROAR that will output the byte stream its virtual ADC reads from a WAV file as the tape loads (CLOAD/CLOADM).

Previously DC.EXE (Dragon Convert) was used to create CAS files from WAV samples but this resulted in CAS files with truncated sync bytes rather than an accurate dump of the original media.




DC.EXE will create a clean WAV sample from a CAS file. If the CAS file has all its SYNC bytes then the resultant WAV can be loaded by a real Dragon 32/64.

"Fixing old CAS files"

Some of the older CAS files with truncated SYNC bytes can be rescued using the FIXCAS.EXE tool that attempts to insert the appropriate number of missing SYNC bytes into the CAS file.

Disk to VDK

Using and old PC with a 5.25 inch drive and a DOS environment, the VCOPY.EXE tool can be used to copy some common Dragon disk formats to .VDK files.

Disk to DMK

Linux - dd


Perl Tool to add VDK header


Perl Tool to remove VDK header

VDK to Disk

Using and old PC with a 5.25 inch drive and a DOS environment, the VCOPY.EXE tool can be used to copy some common Dragon disk formats from .VDK files to disks. The disks must have been formatted in a real Dragon first....

DMK to Disk

Linux - dd

Dumping ROMS

CSAVEM, start, end, exec Convert to CAS Use DC.EXE to extract from CAS to ROM format

.DGN format is a only an 8 byte header that can be removed or added to a raw rom dump.

File Formats

CAS File Format

The CAS file format represents programs or data stored on Dragon cassette tapes. The format closely mimics how the Dragon actually stores data on cassettes, and this format is documented in Inside the Dragon (Section 8.4.4).

A CAS file consists of a number of blocks. Each block contains:

  • A leader, comprising of any number of bytes with value 0x55.
  • A sync byte of value 0x3c.
  • A block type byte. Valid types are 0 for namefile block, 1 for data block and 0xff for EOF block.
  • A byte containing the data payload size (0-255).
  • 0-255 bytes of payload data.
  • A checksum byte. The checksum is the sum of the block type, the payload size and the data bytes.

For a namefile block, the payload data contains the following information:

  • An 8-byte program name.
  • A byte indicating the file type. Valid types are 0 for a BASIC program, 1 for a data file, and 2 for a machine code program.
  • A byte indicating whether the file is encoded as ASCII or binary.
  • A byte indicating whether the file is written with gaps between blocks. A value of 1 indicates that the file is written without gaps, and a value of 0xff indicates that it contains gaps between blocks.
  • Two bytes indicating the start address of a machine code program.
  • Two bytes indicating the load address of a machine code program.

The first block of a CAS file should be a namefile block, and the last block should be an EOF block.

Note that CAS files may omit leaders. Use the FIXCAS utility to add leaders to more closely resemble the true Dragon cassette tape format.

JVC/DSK File Format

A disk format created by Jeff Vavasour for his Tandy emulator series, this is the simplest disk image format. It consists of an optional header followed by the DATA portion of each disk sector in order of track, then side, then sector number.

Taken from Tim Lindner's JVC format documentation, the header is as follows:

Byte Offset Description Default
0 Sectors per track 18
1 Side count 1
2 Sector size code 1
3 First sector ID 1
4 Sector attribute flag 0

Sector size code indicates sector is (128 << n) bytes long. The default of 1 means a sector size of 256 bytes.

The sector attribute flag indicates that each sector is preceeded by an attribute byte. This contains which bits would be set in the WD279x status field after a read sector command, and can indicate record type, record not found and CRC error.

The presence of the sector attribute flag confuses things slightly, as if it is set, suddenly the header size is the file size modulo 257 instead of modulo 256.

VDK File Format

Similar to the JVC/DSK format, this contains a header followed by a raw dump of sector data. Data is in track, then side, then sector number order.

Incomplete header information:

Byte Offset Description
0, 1 'd', 'k'
2, 3 Header size (little-endian)
8 Number of tracks
9 Number of sides

DMK File Format