TNETX15VE datasheet(84/113 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

adding an address

The ADD logic operation is responsible for new address additions to the lookup table, address port changes,

marking the address as NEW, modifying the information stored in the lookup table, and keeping the address

time stamp current. The TNETX15VE implements a single ADD logic operation and shares it between automatic

adds from the wire and host port additions. The TNETX15VE prioritizes wire adds over management adds. It

completes an add request before starting another add request.

The ADD algorithm is summarized as follows:

• ADD performs a lookup to determine if the source address exists in the table.

• If the address exists, ADD verifies that the port assignment has not changed. If the port assignment

changes and the address is not secured, a CHNG interrupt is issued; if the address is secured, a

SECVIO interrupt is issued. If NAUTO = 0 and the address is unsecured, ADD updates the port and sets

the NEW bit. In all cases, ADD updates the AGE time stamp.

• Iftheaddressdoesnotexist,aNEWinterruptisissued.IfNAUTO=0,ADDaddstheaddresstothetable

with the current time stamp and the NEW bit is set.

Adding an address may require allocating additional lookup tables. It is possible that during the adding process

no more lookup tables are available for address additions. A FULL interrupt is issued to the host, and the ADD

operation stalls, pending the resolution of the no-space-available situation. In this situation, the following occurs:

• If the NAUTO bit is set to 1 (host-managing table), the host deletes addresses in the table until enough

are deleted to make space for the new address. Depending on the shared tables used by the addresses

being deleted, and the tables that are shared by the inbound address, it is possible that many addresses

may have to be deleted for the new address to fit. When enough space is available, the ADD operation

completes, as denoted by the ADD bit in the adddelcontrol register, 0x2C, going to 0.

• IftheNAUTObitissetto0(TNETX15VEmanagingtable),theTNETX15VEdeletesasmanyaddresses

as necessary to fit the new address into the table by deleting the oldest addresses, using the AGE

function.

The following modes indicate control and other options that affect the ADD logic operation.

NAUTO mode

NAUTO mode is selected by setting the NAUTO bit in the control register to 1. In NAUTO mode, the ADD logic

operation does not add addresses off the wire. The only way addresses are added, moved, or edited is through

the register interface. The wire ADD state machine does continue checking addresses going by on the wire,

but the host processor must act on an indication of a new address to have that address placed in the table.

TNETX15VE 数据表(PDF) 84 Page - Texas Instruments

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