The stream format is composed of:
- a header
- one or more frames
- a footer
The 3-bytes LZSA header contains a signature and a traits byte:
0 1 2 0x7b 0x9e 7 6 5 4 3 2 1 V V V Z Z Z Z <--- signature ---> <- traits ->
- V: 3 bit code that indicates which block data encoding is used. 0 is LZSA1 and 1 is LZSA2.
- Z: these bits in the traits are set to 0 for LZSA1 and LZSA2.
Each frame contains a 3-bytes length followed by block data that expands to up to 64 Kb of decompressed data. The block data is encoded either as LZSA1 or LZSA2 depending on the V bits of the traits byte in the header.
0 1 2 DSZ0 DSZ1 U|DSZ2
- DSZ0 (length byte 0) contains bits 0-7 of the block data size
- DSZ1 (length byte 1) contains bits 8-15 of the block data size
- DSZ2 (bit 0 of length byte 2) contains bit 16 of the block data size
- U (bit 7 of length byte 2) is set if the block data is uncompressed, and clear if the block data is compressed.
- Bits 1..6 of length byte 2 are currently undefined and must be set to 0.
The stream ends with the EOD frame: the 3 length bytes are set to 0x00, 0x00, 0x00, and no block data follows.