Page History

...

Based on experience of implementing PGP Version 3, we determined that only 1 USER K-code was all that's needed.  In Version 4, we reduce the number of USER codes from 8 to 1 which help reduce the gate logic resource usage. This also leaves 7 reserved BTF codes available for future use.

Difference between PGP4 to Pgp4Lite

PGP Version 4 Lite (Pgp4Lite) is nearly identical to PGP Version 4 (Pgp4).  But Pgp4Lite only supports a subset of all the Version 4 features.  Here are the features that are not supported in Pgp4Lite:

• no SOC (Start of Cell)
• no EOC (End of Cell)
• no VC (Virtual Channel) interleaving

Link Layer

PGP4 uses 64b/66b encoding to achieve DC balance of the serial data stream. Each 64-bit word is scrambled with a source synchronous scrambler with polynomial G(x)=x⁵⁸+x²⁹+1. Two bits are then appended to each word, 0b01 to mark regular data, and 0b10 to mark control characters (K-Codes). This ensures that a transition between 0 and 1 at least once every 66 bits. It is also used for word alignment. These 66-bit words can then be serialized and deserialized using the high speed transceivers found in modern FPGAs. The protocol does not specify any link rates, and any link speed may be targeted provided that the link medium and FPGA on each side can support it.

...