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The MU9C8358L, when configured with MUSIC
Semiconductors MU9Cx480B family of LANCAMs,
provides a high performance, large capacity Ethernet
address processing subsystem for use in Ethernet bridge,
switch, or remote access products. The device is designed
to work in multi-port systems that require a common
address database for all ports. Built-in arbitration allows
two MU9C8358L devices to share a common CAM
database, supporting up to eight 100Mb/s Ethernet ports at
wire speed.
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Because of the flexibility of the MU9C8358L, the best
way to approach the feature set of the device is to first
look at a typical Multiport 10/100Mb Ethernet application.
The MU9C8358L captures the Destination address (DA)
and the Source address (SA) of an incoming Ethernet
frame on the MII port. After checking for a frame error or
collision, the DA is processed and the result (associated
data, usually a port ID) is made available. The SA then is
checked, and either learned if new, or aged if already in the
list.
When the DA is processed, the MU9C8358L first checks
if the frame is Unicast, Multicast, or Broadcast. Unicast
frames destined for the same collision domain (visible on
the same switch port as it came in on) are rejected. Unicast
frames that are destined for a different collision domain
(visible on a different switch port) are processed by the
system. If the DA is found in the CAM database, the port
ID associated with it is stored in the Result register.
Multicast and Broadcast frames are not processed by the
system. Instead they are identified and their classification
is stored in the Result register. Once processing completes,
the Result register is accessed through the Result port or
Processor port.
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The MU9C8358L plays an integral role in the example of
an Ethernet switching system, shown in Figure 2.
Provided the frame length is correct, and no errors are
detected, the SA is processed. If the SA exists in the CAM
database, the time stamp and Port ID are updated. If the
SA is not found in the CAM database, the address is
learned automatically, along with its Port ID and the
current time stamp information.
This system can handle up to 32,768 addresses distributed
over eight independent, bidirectional 100Mb Ethernet
ports by utilizing two MU9C8358L devices and four
LANCAMs connected as shown in Figure 1. The system is
based on several industry-standard and proprietary busses,
which are described in more detail later. The MII bus is
"tapped" to collect packet data as it passes from the PHY
to the MAC. That data is processed automatically by the
MU9C8358L/LANCAM combination. The LANCAM
bus is utilized to transfer the DA and SA to the CAMs for
comparisons, and to transfer the match results from the
CAMs to the MU9C8358L. The results of
MU9C8358L/LANCAM data processing are available
through the Result bus or through the Processor bus. In
addition to the Result bus, there is a serial Tag port per MII
port to relay the Tag ID to the system for systems that
support Tag switching. The Arbitration bus provides
communication between two MU9C8358L devices to
service eight MII ports with a shared CAM-based station
list.
The built-in arbitration allows all ports equal access to the
CAM database. The arbitration scheme gives DA
processing the highest-priority, then SA processing.
Address processing always has priority over management
routines, such as purging aged entries, inserting permanent
entries, deleting entries, or reading from the CAM
database. Using the 70 ns speed grade CAMs and a 50
MHz system clock, there is sufficient time to support eight
DA searches, eight SA searches, and one management
routine, within the minimum frame time (about 6.2µS). In
addition, the arbitration bus allows the MU9C8358L to be
used with future MUSIC devices, sharing a common CAM
database.
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MUSIC [ MUSIC SEMICONDUCTORS ]
