TNETX15AE datasheet(56/78 Pages) TI

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TNETX15AE

ADDRESS-LOOKUP DEVICE

SPWS041A – AUGUST 1997 – REVISED OCTOBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

summary of FIND operations supported

Table 8 summarizes the supported FIND operations, the bits used to select the operation, and the code written

to the findcontrol register.

Table 8. FIND Operations

OPERATION

BITS USED

FINDCONTROL

FIND (LKUP)

LKUP

0x01

FINDNEXT

0x02

FINDFIRST

FIRST

0x04

adding an address

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

modifying the information stored in the lookup table, and keeping the address time stamp current. The

TNETX15AE implements a single ADD logic operation and shares it between automatic adds from the wire and

host port additions. The TNETX15AE prioritizes wire adds over management adds. It completes an add request

before starting another request.

The ADD algorithm is summarized as follows:

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

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

changes, ADD updates the port. In all cases, ADD updates the AGE time stamp.

D If the address does not exist, ADD adds the address to the table with the current time stamp.

Currently, adding an address requires available lookup tables. It is possible that during the ADD operation 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.

D 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.

D If the NAUTO bit is set to 0 (TNETX15AE managing table), the TNETX15AE deletes as many addresses

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

interrupts available to support both wire ADDs and host ADDs

The following interrupts are active, regardless of the state of NAUTO, to support monitoring of addresses added

to the table (subject to the bandwidth available to look up source addresses):

D NEW and NEWM interrupts are indicated when a new address is found.

D CHNG and CHNGM interrupts are indicated when the address is not new but the port assignment

is changed.

D SECVIO and SECVIOM interrupts are indicated when the address is not new, the port assignment is

changed, and the address is secured.

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

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