TNETX15VE datasheet(76/113 Pages) TI1

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TNETX15VE

VLAN-ENGINE ADDRESS-LOOKUP DEVICE

SPWS028B – APRIL 1997 – REVISED SEPTEMBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

TNETX15VE operational modes

The TNETX15VE operational modes are selected through the control register. They are used to control decision

points in the logic operations. The modes available through the control register are NAUTO, NCRC, and MIRR.

Other operating parameters are selectable through the agingtimer, NLRNports, TXblock, and RXblock

registers.

NAUTO mode

The not automatically add-address (NAUTO) mode is implemented to give the management CPU complete

control of the lookup table. It does so by disabling the two automatic processes that can affect the lookup-table,

wire additions, and aging.

NAUTO mode disables adding addresses to the TNETX15VE tables learned from packets passing through the

TNETX3150/TNETX3150A. All addresses in the TNETXVE must be added through the DIO interface (see ADD

in internal register section). No interrupt is generated on addresses added through the DIO interface, even if

the host sets the NEW bit in the addport register so that the address can be found with a FINDNEW command.

NEW interrupts in this mode signal that the address checking state machine has seen an address on the wire

that is not in the table.

NAUTO also affects the AGE logic operation by disabling it. AGE does not delete nodes from the table even

if the table is full. It is the management’s responsibility in this mode to maintain the addresses in the lookup table.

Table-full conditions are determined through a FULL interrupt.

NCRC mode

The no-CRC (NCRC) check mode enables the TNETX15VE to add addresses learned from packets before the

CRC is checked. It is a performance-boosting feature for the ADD state machine and it allows it to perform more

ADD logic operations in the same amount of time. This allows the TNETX15VE to add more efficiently and keep

the aging time stamp current on nodes that do not talk frequently on the network, avoiding unnecessary aging.

The tradeoff in this mode is the possibility that corrupt addresses could be added into the lookup table. This

condition should not become critical unless aging is turned off.

MIRR mode

The mirrors activity (MIRR) mode directs all of a port’s traffic to a user-specified port. This, in effect, mirrors the

activity to the selected port. Three types of traffic are copied: traffic that is directed to the port, traffic that is

coming from the port, and traffic that stays within the port’s segment and would ordinarily be discarded. MIRR

mode may decrease performance in the switch since it generates additional traffic within the

TNETX3150/TNETX3150A.

aging modes (agingtimer register)

The TNETX15VE implements an autonomous aging logic operation. There are two modes of aging and these

modes are controlled through the agingtimer register. The two modes are time-threshold aging and table-full

aging.

Time-threshold aging is set by writing a value between 0x0001 and 0xFFFE to this register. In this mode, the

provides an aging range of 1 second to 18 hours. Addresses older than this are deleted.

Table-full aging is set by writing 0x0000 or 0xFFFF to the register. In this mode, the AGE logic operation ages

out addresses only when the table is full and the ADD logic operation needs to add an address. AGE deletes

the oldest address in the table.

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