AR8327-AL1A-R datasheet(47/394 Pages) ETC2

47 / 394 page

Atheros Communications, Inc.

AR8327/AR8327N Seven-port Gigabit Ethernet

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2.17.3

Forwarding Unknown

The AR8327 can be configured to prevent the forwarding of unicast frames and multicast frames with

unregistered destination MAC address on per port base. This can be done by setting UNI_FLOOD_DP

and MULTI_FLOOD_DP where a bit represents a port of the AR8327.

2.17.4

MAC Limit

The AR8327 supports MAC limit on a per-port basis or a global basis. When the number of learned

MAC address limit is reached, the AR8327 can be configured to forward a frame with a new source

MAC address to the CPU or it can be dropped.

2.18 Spanning Tree

IEEE 802.1D Spanning Tree allows bridges to automatically prevent and resolve Layer 2 forwarding

loops. Switches exchange BPDUs and configuration messages and selectively enable and disable

forwarding on specified ports. A tree of active forwarding links ensures an active path between any

two nodes in the networks. Spanning Tree can be enabled globally or on a per-port basis by

configuring the Port Status register.

2.18.1

EEPROM Programming Format

Figure 2-4 shows the EEPROM programming format. Note that the last register should be at

address 0, and the LOAD_EEPROM bit written to 1'b0 to stop the load EEPROM state machine.

2.18.2

Basic Switch Operation

The AR8327 automatically learns the port number of an attached end station by looking at the source

MAC address of all incoming packets at wire speed. If the source address is not found in the address

table, the AR8327 device adds it to the table. Once the MAC address/port number mapping is learned,

all packets directed to that end station’s MAC address are forwarded to the learned port number only.

When the AR8327 device receives incoming packets from one of its ports, it searches in its address

table for the destination MAC address, then forwards the packet to the appropriate port within the

VLAN group. If the destination MAC address is not found (i.e. a new, unlearned MAC address), the

AR8327 handles the packet as a broadcast packet and transmits it to all ports within the VLAN group

except to the port where it came in.

2.18.3

Lookup Engine

The AR8327 lookup engine or address resolution logic (ARL) retrieves the DA and SA from each frame

received from each port. The ARL performs all address searching, learning, and aging functions at

wire speed. The ARL engine uses a hashing algorithm for fast storage and retrieval of address entries.

To avoid hash collision, the AR8327 uses a three-entry bin per hash location that stores up to three

MAC addresses at each hash location. The address database is stored in the embedded SRAM and has

a size of 2048 entries.

Figure 2-4.

EEPROM Programming Format

C0DE

Switch register

Checksum[15:0]

Addr[13:2]

Data[15:0]

Data[31: 16]

High addr[4:0]

10'b0

High addr

4'b0

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