|author||Nigel Barnes <Pernod70@users.noreply.github.com>||2018-03-06 17:41:45 +0000|
|committer||Nigel Barnes <Pernod70@users.noreply.github.com>||2018-03-06 17:41:45 +0000|
jvc_dsk: Added notes (nw)
Diffstat (limited to 'src/lib')
1 files changed, 93 insertions, 2 deletions
diff --git a/src/lib/formats/jvc_dsk.cpp b/src/lib/formats/jvc_dsk.cpp
index d2e7e503d3b..3056a311169 100644
@@ -6,10 +6,101 @@
Disk image format
- Named after its creator, Jeff Vavasour
+ Used by Jeff Vavasour's CoCo Emulators
+ Documentation taken from Tim Linder's web site:
+ A. Header length
+ The header length is determined by the file length modulo 256:
+ headerSize = fileLength % 256;
+ This means that the header is variable length and the minimum size
+ is zero bytes, and the maximum size of 255 bytes.
+ B. Header
+ Here is a description of the header bytes:
+ 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
+ If the sector attribute flag is zero then the track count is determined
+ by the formula:
+ (fileLength - headerSize) / (sectorsPerTrack * (128 <<
+ sectorSizeCode)) / sideCount
+ If the sector attribute flag is non zero then the track count is
+ determined by the more complex formula:
+ (fileLength - headerSize) / (sectorsPerTrack * ((128 <<
+ sectorSizeCode) + 1) ) / sideCount
+ If the length of the header is to short to contain the geometry desired,
+ then the default values are assumed. If the header length is zero the all
+ of the geometry is assumed. When creating disk images it is desirable to
+ make the header length as short as possible. The header should only be
+ used to deviate from the default values.
+ The sector data begins immediately after the header. If the header length
+ is zero then the sector data is at the beginning file.
+ C. Sectors per track
+ This is the number of sectors per track (ones based). A value of 18
+ means there are 18 sectors per track
+ D. Side Count
+ This is the number of sides in the disk image. Values of 1 or 2 are
+ acceptable. If there are two sides then the tracks are interleaved.
+ The first track in the image file is track zero side 1, the second
+ track in the image file is track zero side 2.
+ E. Sector size
+ The is the same value that is stored in the wd179x ID field to
+ determine sector size:
+ 0x00 128 bytes
+ 0x01 256 bytes
+ 0x02 512 bytes
+ 0x03 1024 bytes
+ Other values are undefined. Every sector in the disk image must be the
+ same size.
+ F. First sector ID
+ This determines the first sector ID for each track. Each successive
+ sector adds one to the previous ID. If the first sector ID is 1, then
+ the second sector has an ID of 2, and the third has an ID of 3.
+ G. Sector Attribute Flag
+ If this byte is non zero, then each sector contains an additional
+ byte prepended to the sector data. If the attribute flag is zero then
+ there are no extra bytes in front of the sector data.
+ H. Sector attribute byte
+ This byte is put at the beginning of every sector if the header flag
+ is turned on. The information this byte contains is the same as the
+ status register (of the wd179x) would contain when a 'Read Sector'
+ command was issued. The bit fields are defined as:
+ Bit position:
+ 7 6 5 4 3 2 1 0
+ | | | | | | | |
+ | | | | | | | +--- Not used. Set to zero.
+ | | | | | | +----- Not used. Set to zero.
+ | | | | | +------- Not used. Set to zero.
+ | | | | +--------- Set on CRC error.
+ | | | +----------- Set if sector not found.
+ | | +------------- Record type: 1 - Deleted Data Mark, 0 - Data Mark.
+ | +--------------- Not Used. Set to zero.
+ +----------------- Not Used. Set to zero.
- - Support writing unusal formats?
+ - Support writing unusual formats?