TNETX15VE datasheet(83/113 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

FIFO FINDS (NBFR–no broadcast FIFO reads)

In certain applications, such as spanning tree, it is important to know the source address of frames sent to a

common-destination address. The TNETX15VE gives the programmer the capability of doing this, but limits this

to only those frames whose destination address is marked with the NBLCK bit.

The TNETX15VE performs a destination address search on all frames going by on the DRAM bus. If the

destination address matches one on the lookup table, and if the matching address on the lookup table has the

NBLCK bit set, the TNETX15VE writes the source address of this frame into the NBLCK RXFIFO, regardless

of whether or not the receiving port is being RX blocked. The TNETX15VE then informs the host that the FIFO

contains data by asserting an RXFIFO interrupt (RXFIFO bit in the interrupt and intmask registers). The NBLCK

FIFO entries are made as a result of the LKUP operation. An entry is made even if the packet has a bad CRC.

The TNETX15VE FIFO reads the NBLCK RXFIFO using the FIND state machine. The procedure for performing

FIFO reads is as follows.

• Perform a FIFO read:

Set the NBFR bit in the findcontrol register. No write to any other register is required. The

TNETX15VE scans the FIFO for the first address.

Poll the findcontrol register until the NBFR bit clears. No FNDCMPLT interrupt is given due to the

speed of the FIFO read. At most, one poll is required.

Read the findcontrol register. If the FOUND bit is set, then an address was found and the node’s

address is given in the findnode register. The frame’s tag and the port the frame originated from is

placed in the findport register. This address is then cleared from the FIFO. If the FOUND bit is not

set, then an address was not found and the FIFO is empty.

Repeat the NBFR operation until no more addresses are found.

summary of FIND operations supported

Table 5 summarizes the supported FIND operations, the bits used to select the operation, and the code written

to the findcontrol register.

Table 5. FIND Operations

OPERATION

BITS USED

FINDCONTROL

FIND (LKUP)

LKUP

0x01

FINDNEXT

0x02

FINDFIRST

FIRST

0x04

FINDNEXTVLAN

VLAN, NEXT

0x0A

FINDFIRSTVLAN

VLAN, FIRST

0x0C

FINDNEXTPORT

PORT, NEXT

0x12

FINDFIRSTPORT

PORT, FIRST

0x14

FINDNEXTPORTVLAN

PORT, VLAN, NEXT

0x1A

FINDFIRSTPORTVLAN

PORT, VLAN, FIRST

0x1C

NBLCK FIFO READ

NBFR

0x20

FINDNEW

NEW

0x40

FINDNEWVLAN

NEW, VLAN

0x48

FINDNEWPORT

NEW, PORT

0xA0

FINDNEWPORTVLAN

NEW, PORT, VLAN

0xA8

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