Aside from the usual clk and rst signals, the only input to the entity is an AXI-Stream with a width of one byte. The data stream consists of frames encoded according to the rules described in Consistent Overhead Byte Stuffing by Stuart Cheshire and Mary Baker. These rules convert a known-length stream of bytes (a “frame”) with all values 0-255 into a slightly longer stream of bytes containing only values 1-255, allowing a byte with value 0 to be used unambiguously as a separator. It does this by dividing the stream into sequences of bytes. Each sequence must consist of zero to 253 non-zero bytes followed by a 0 byte or the end of stream, or 254 non-zero bytes. It is then encoded as the sequence length (1 to 254) followed by the non-zero bytes.
Read the rest at:
https://github.com/phase4ground/adi_adrv9371_zc706/blob/adrv9371-zc706-dvbs2-integ/design_docs/cobs_decoder/COBS_dec-Entity-Design.md