Difference between revisions of "DFI image format"
(Added comments, thanks fjkraan!) |
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add_index_position(carry) // add high bit to carry | add_index_position(carry) // add high bit to carry | ||
else: // here byte < 0x7f | else: // here byte < 0x7f | ||
− | emit((byte AND 0x7f) + carry) // | + | emit((byte AND 0x7f) + carry) // report carry + byte |
carry = 0 // reset carry | carry = 0 // reset carry | ||
if carry > 0: // | if carry > 0: // | ||
emit(carry) // report carry | emit(carry) // report carry | ||
− | // emit() | + | // emit() stores the timing value |
− | // add_index_position() | + | // add_index_position() stores the timing position of an index pulse |
// | // | ||
</nowiki> | </nowiki> |
Revision as of 01:45, 16 January 2012
Format originator: DiscFerret software.
Overall format
All integers in this file format are stored in big-endian form.
The DFI file consists of a 4-byte magic string, followed by a series of disc sample blocks.
The magic string is "DFER" for old-style DiscFerret images, or "DFE2" for new-style DiscFerret images.
Each sample block has a header --
uint16_be cylinder; uint16_be head; uint16_be sector; uint32_be data_length;
The cylinder number starts at zero and counts up to the number of cylinders on the disk. The head number follows the same rule (starts at zero, increments for each additional head). The sector number is optional, and only used for hard-sectored discs. For soft-sectored discs, it is set to zero. Data_length indicates the number of bytes of data which follow.
Decoding data
Old-style images
carry = 0 For every byte in the stream: if (byte AND 0x7f) == 0x00: carry = carry + 127 else: emit((byte AND 0x7f) + carry) carry = 0 if carry > 0: emit(carry)
New-style images
carry = 0 For every byte in the stream: if ((byte AND 0x7f) == 0x7f): // if lower 7 bit value is 0x7f carry = carry + 127 else if (byte AND 0x80) != 0: // if high bit set in byte carry = carry + (byte & 0x7F) // add lower 7 bit value to carry add_index_position(carry) // add high bit to carry else: // here byte < 0x7f emit((byte AND 0x7f) + carry) // report carry + byte carry = 0 // reset carry if carry > 0: // emit(carry) // report carry // emit() stores the timing value // add_index_position() stores the timing position of an index pulse //