ASIX ELECTRONICS CORPORATION

19

CONFIDENTIAL

AX88872P Swipeater Controller

PRELIMINARY

collision, each port uses a partition state machine to detect and prevent this condition. When a port suffers from

continuous 64 times of collision events, then it goes to Partition State. The partitioned port will be not released

until a packet without collision be transmitted( more than 512 bit times for AX88872) or reset the repeater.

3.5 Operation of the Built-In Switch

In general, the basic operation of the switch is very simple. The switch receives incoming packets from one of its ports,

searches in the Look-Up Table for the Destination MAC Address and then forwards the packet to the destination ports,

if appropriate. If the destination MAC address is not found in the Look-Up Table, the switch treats the incoming packet

as a broadcast packet and forwards it to all ports except itself. Basically the switch automatically learns the port number

of attached network devices by examining the Source MAC Address of all incoming packets. The device is updated the

table with the Source MAC Address if the Source MAC Address does not exist the table.

3.5.1 Packet Filtering and Forwarding Process

During the receiving process, the switch will monitor the length of the received packet. Legal Ethernet packets should

have a length of no less 64 bytes and nor more than 1528 bytes. The switch discards any packet with illegal length.

After a packet is received, its Source MAC Address and Destination MAC Address are received. The Source MAC

Address is used to update the Look-Up Table and the Destination MAC Address is used to determine the destination port

of the packet. Once a MAC Address has been learned, and the packet is buffered, it must be forwarded, That is, the packet

forwarding mechanism for the switch is handled automatically based on the destination MAC Address.

Under the following conditions, received packets are filtered:

The switch supports three forwarding modes: Store-and-Forward, Fragment-Free and Auto.

is forwarded. That is, each forwarded packet is correct.

packet whose packet length is more than 64 bytes. All runt packets will be filtered in Fragment-Free

mode.

current network quality of each port.

3.5.2 MAC Address Learning and Aging Process

The switch can learn up to 8K unique MAC addresses with a hashing algorithm. Addresses are stored in the Look-Up

Table located in external SSRAM, then each packet updates the table.

The table lookup engine provides the switching information required routing the data packets. The address table is set up

through auto address learning dynamically. After the switch receives a packet, the Source MAC Address and Destination

MAC Address are received. The Source Address retrieved from the received packet is automatically stored in a SA

buffer. The switch will check for error and perform a SA search. The switch will update the Look-Up Table with the

Source MAC Address if there is no error.

The Look-Up Table is cleared on power-on, or hardware reset. When the aging option is enabled, the dynamically

Learned SA will be cleared if it is not refreshed in less than configured time (2 or 5 min).

3.5.3 Flow Control Process

The switch can operate at two different modes: half-duplex and full-duplex. Each port can be configured to have flow

control enabled or not. The switch supports 802.3X for full-duplex operation and uses back pressure for half-duplex.

In full-duplex mode, the switch will receive and transmit the packet in accordance to 802.3X. The transmission channel

and the receiving channel operate independently. If the occupancy of the buffer memory is above the FlowControlActive