TNETX15AE datasheet(60/78 Pages) TI

60 / 78 page

TNETX15AE

ADDRESS-LOOKUP DEVICE

SPWS041A – AUGUST 1997 – REVISED OCTOBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

table-full aging

Table-full aging is implemented for applications that do not want to use aging based on time, but still require

aging. As its name implies, aging in this mode only happens when the lookup table is full and needs additional

room to add a new address. The ADD logic operation initiates an aging request when it determines that it does

not have enough tables to add the address it is working on. The time behaves differently in this mode. In table-full

aging, the age timer does not increment every second, but rather when a new address is added. There must

be a time difference between addresses to decide which is oldest, but a single count is sufficient. Since ADD

time stamps every time it sees an address come through the bus, nodes that are actively transmitting between

adds quickly move up to the same (new) age level. Those nodes that do not transmit remain at the lower age

stamps. It is these nodes that are deleted in table-full aging when the table is full.

DEL logic operation (management address deletions)

BYTE 3

BYTE 2

BYTE 1

BYTE 0

DIO

ADDRESS

Adddelcontrol

0x2C

Delnode23–Delnode16

Delnode31–Delnode24

Delnode39–Delnode32

Delnode47–Delnode40

0x48

Delnode7–Delnode0

Delnode15–Delnode8

0x4C

The DEL logic operation is controlled through the delnode and the adddelcontrol register. Management delete

commands are given through the DEL bit in the adddelcontrol register.

The steps for deleting a particular address (multicast or unicast) are as follows:

D Writing the node address in the delnode register

D Asserting the DEL bit in adddelcontrol

The DEL logic operation locks the delnode on all delete commands to ensure that they do not change during

the deletions. Reads to these registers are still possible. The DEL bit in adddelcontrol remains in the 1 state until

the deletion is complete.

Much like the management adds, having a sticky bit for DEL gives the programmer the opportunity to set up

or perform other register operations without having to wait for the delete completion. A polling method is used

to find out if the delete is finished. This involves reading adddelcontrol to determine if the command bit used

has returned to 0.

interrupts

The TNETX15AE implements interrupts to ease the management processor’s tasks. The interrupts are used

to indicate changes to the lookup table. It indicates that a new address is added, an address changed ports,

an address changed ports and is secure, and an address is deleted due to the aging process. The statistic

registers are half full (and the possibility for an overflow is present) and the lookup table is full. The TNETX15AE

indicates that interrupts to the CPU exist by setting to 1 its level-sensitive EINT terminal. The EINT terminal is

asserted when any of the possible interrupt conditions are met and the condition(s) is(are) enabled.

The interrupt register is readable at all times and contains all the current TNETX15AE interrupts. The interrupt

is masked or not.

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