yosys/libs/fst/block_format.txt

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See fstapi.h for the values for the FST_BL_XXX enums.
===========================================================================
compressed wrapper (typically over whole file)
uint8_t FST_BL_ZWRAPPER
uint64_t section length
uint64_t length of uncompressed data
[zlib compressed data]
===========================================================================
header block
uint8_t FST_BL_HDR
uint64_t section length
uint64_t start time
uint64_t end time
double endian test for "e"
uint64_t memory used by writer
uint64_t scope creation count
uint64_t var creation count
uint64_t max var idcode
uint64_t vc section count
int8_t timescale exponent
[128 bytes] version
[128 bytes] date
===========================================================================
geometry block
uint8_t FST_BL_GEOM
uint64_t section length
uint64_t length of uncompressed geometry data
uint64_t maxhandle
[compressed data]
(length of compressed data is section length - 24)
===========================================================================
hierarchy block
uint8_t FST_BL_HIER
uint64_t section length
uint64_t length of uncompressed hier data
[zlib compressed data]
or
uint8_t FST_BL_HIER_LZ4
uint64_t section length
uint64_t length of uncompressed hier data
[lz4 compressed data]
uint8_t FST_BL_HIER_LZ4DUO
uint64_t section length
uint64_t length of uncompressed hier data
varint length of hier data compressed once with lz4
[lz4 double compressed data]
===========================================================================
dumpon/off block
uint8_t FST_BL_BLACKOUT
uint64_t section length
varint num blackouts (section below is repeated this # times)
[
uint8_t on/off (nonzero = on)
varint delta time
]
===========================================================================
1..n value change blocks:
// header
uint8_t FST_BL_VCDATA (or FST_BL_VCDATA_DYN_ALIAS)
uint64_t section length
uint64_t begin time of section
uint64_t end time of section
uint64_t amount of buffer memory required in reader for full vc traversal
varint maxvalpos (length of uncompressed data)
varint length of compressed data
varint maxhandle associated with this checkpoint data
[compressed data]
---
// value changes
varint maxhandle associated with the value change data
uint8_t pack type ('F' is fastlz, '4' is lz4,
others ['Z'/'!'] are zlib)
varint chain 0 compressed data length (0 = uncompressed)
[compressed data]
...
varint chain n compressed data length (0 = uncompressed)
[compressed data]
---
// index: chain pointer table (from 0..maxhandle-1)
varint if &1 == 1, this is <<1 literal delta
if &1 == 0, this is <<1 RLE count of zeros
if == 0, next varint is handle of prev chain to use,
bit only if FST_BL_VCDATA_DYN_ALIAS or
later VCDATA format
---
uint64_t index length (subtract from here to get index position)
---
[compressed data for time section]
uint64_t uncompressed data length in bytes
uint64_t compressed data length in bytes
uint64_t number of time items
// end of section
===========================================================================