A dedicated bandwidth switch backplane has efficient receive processing capable
of handling highly parallel traffic. Packets must pass a filtering check and a
watermark check before the receive port is allowed to release them to a queue.
Highly efficient algorithms are applied to conduct the checks on the packets in
a way which expedites receive processing and avoids contention. A hybrid priority/port-based
arbitration algorithm is used to sequence filtering checks on pending packets.
A watermark comparison algorithm performs preliminary calculations on the current
packet using "projected" output queue write addresses for each possible outcome
of the queueing decision on the preceding packet and using the actual outcome to
select from among preliminary calculations to efficiently address the outcome-dependence
of the current packet's watermark check on the queueing decision made on the preceding
packet. Receive ports are operatively divided into full-write receive ports and
selective-write receive ports for delivering their packets to the output queue.
On the clock cycles where the selective-write receive port is assigned writing
privileges, data is read from the queue, unless the selective-write receive port
has indicated it wishes to write to the queue, in which case the selective-write
receive port writes to the queue. The full-write receive ports always write data,
if available, to the queue on the clock cycles where they are assigned writing privileges.