Subversion Repositories srdydrdy_lib

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  Example Bridge / Switching Hub
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The bridge directory contains an example bridge built using
srdy-drdy components.  It could more accurately be called
a switching hub, since it does not implement spanning tree
or QoS.

The bridge is designed for simplicity rather than efficiency,
as the purpose is not to make a functioning product but to
demonstrate use of the library.

The bridge design pushes the bulk of the logic into each
individual port, called a port_macro.  The only global logic
is the FIB (Forwarding Information Block) that contains the
address lookup and learning logic, and a centralized ring
arbiter.

The port_macros are connected to each other via a ring interface.
Only one packet can be transmitted on the ring at a time.
The system is designed so that it has more ring bandwidth than
the maximum amount of incoming traffic, so that the ring should
not be the bottleneck for system performance.

The bridge is designed to be output-queued, so that all packets
are forwarded to their output port and the output port will
drop packets if there is insufficient transmit bandwidth.

The bridge handles all transmission errors on the input port,
using the rx_fifo to drop packets which arrive with bad CRC.
The parser waits until the end of packet is received to determine
if the packet is good, and only sends the packet to the FIB
if CRC is OK.  Otherwise the parser errors the packet so it
will be dropped in RX FIFO.

Packets are transmitted and received using an 8-bit GMII interface.
In order to create a higher-bandwidth internal interface, data
is aggregated into 64-bit words to get 8x bandwidth.  This gives
the internal ring roughly 2x the bandwidth of all receiving ports
combined.