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84 lines
2.1 KiB
Plaintext
84 lines
2.1 KiB
Plaintext
=== Bitstream Data Block (`BITS`)
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The `BITS` block contains a list of all known bitstream captures.
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A *bitstream* is derived by interpreting flux transitions using an encoding scheme timing table.
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While bitstreams sit below sector-level data in the hierarchy, they are still a higher abstraction than raw flux transitions.
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Storing bitstream data is valuable because multiple dumps from the same media often produce inconsistent and incomparable flux transitions.
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However, once decoded into bitstreams—regardless of whether sector-level user data can be extracted—the results remain consistent and comparable.
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Bitstream-level representations are also preferred in low-level emulation scenarios.
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Emulators, such as floppy drive emulators, can reconstruct original media more effectively using bitstream data than flux data.
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Bitstream data is stored in `DataBlocks` with the `bitstream` data type.
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Each image must contain exactly one deduplication table of this data type, and that table must have a single level.
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NOTE: Bitstream deduplication tables provide a reference for associating bitstream captures and their corresponding data blocks.
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==== Structure Definition
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[source,c]
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/* Undefined */
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==== Field Descriptions
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[cols="2,2,2,6",options="header"]
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|===
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|Type
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|Size
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|Name
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|Description
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|uint32_t
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|4 bytes
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|identifier
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|The flux data block identifier, always `BITS`
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|uint16_t
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|2 bytes
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|entries
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|The number of entries following this header
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|uint64_t
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|8 bytes
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|crc64
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|The CRC64-ECMA checksum of the data following this header
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|===
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==== Bitstream entries
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[source,c]
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/* Undefined */
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==== Field Descriptions
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[cols="2,2,2,6",options="header"]
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|===
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|Type
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|Size
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|Name
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|Description
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|uint32_t
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|4 bytes
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|head
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|Head the data corresponds to.
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|uint16_t
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|2 bytes
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|track
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|Track the data corresponds to.
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|uint8_t
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|1 byte
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|subtrack
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|Substep of a track that the data corresponds to.
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|uint64_t
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|8 bytes
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|tableEntry
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|Entry number in the deduplication table where the data corresponding to this bitstream entry is stored
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|===
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To better understand the relationship between user data, bitstream data and flux data please refer to _Annex F_. |