Transmit Pending Array (TPA) 1 x 1 Gbps configuration
4 arrays are used to provide 32 x 32 4-bit values.
The array is split into four vectors: one for each priority level.
The vectors contains a 4-bit status value for each of 256 input ports.
A status value is incremented by a QA arrival and decremented by a DB with EOF=1 arrival.