ACD82224 Datasheet, PDF (65/77 Pages) List of Unclassifed Manufacturers – 24 Ports 10/100 Fast Ethernet Switch

2. FEATURES
• Supports up to 2,048 internal MAC address lookup
• Provides UART type of interface for management CPU
• Wire speed address lookup time.
• Wire speed address learning time.
• Address can be automatically learned from switch without external CPU intervention
• Address can be manually added by the CPU through CPU interface
• Each MAC address can be secured by the CPU from being changed or aged out
• Each MAC address can be marked by the CPU from receiving any frame
• Each newly learned MAC address is notified to the CPU
• Each aged out MAC address is notified to the CPU
• Automatic address aging control, with configurable aging period
3. FUNCTIONAL DESCRIPTION
The internal ARL provides Address Resolution service for the switch controllers. Figure-1 is a
block diagram of the ARL.
Traffic Snooping
All Ethernet frames received by the switch controller have to be stored into memory buffer. As
the frame data are written into memory. The status of the data shown on the data bus is
displayed by the switch controller through the SWSTAT[3:0] bus. The ARL interface with the
Switch Controller contains the signals of the data bus and the state bus. By snoop the data bus
and the state bus of the switch controller, the internal ARL can detect destination MAC address
and source MAC address embedded inside each frame.
Address Learning
Each source MAC address extracted from the data bus, along with the ingress port ID, is passed
to the Address Learning Engine of the ARL.
1. The Address Learning Engine first determines whether the frame is a valid frame.
2. For a valid frame, it will first try to find the source address from the current address table.
3. If that address is not listed, OR the port ID associated with the listed MAC address does not
match the ingress port ID, it will be learned into the address table as a new address.
4. After an address is learned by the address learning engine, the CPU can be notified to read
this newly learned address so that it can add it into the CPU’s address table.
5. If the Address Table is full, Address Learning Engine will not learn any the new MAC address
unless there is new entry available (i.e. Address aging-out).
Address Aging
After each source address is learned into the address table, it has to be refreshed at least once
within each address aging period. Refresh means it is caught again from the switch interface. If it
has not occurred for a pre-set aging period, the Address Aging Engine will remove the address
from the address table. After an address is removed by the address aging engine, the CPU can
be notified through interrupt request that it needs to read this aged out address so that it can
remove this address from the CPU’s address table.
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