TNETX15VE datasheet(80/113 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

FIND, FINDFIRST, FINDNEXT, and FINDNEW commands (continued)

The FINDFIRST command finds the first address contained in the lookup table. The procedure for the FIND

command is as follows:

• Set the FIRST bit in the findcontrol register. No write to findnode or findVLANID is required. The

TNETX15VE scans the lookup table for the first address. The search is confined to a VLAN and/or

PORT by setting those modifier bits in the findcontrol register.

• WaituntiltheFNDCPLTinterruptisasserted[FNDCPLT(bit6)ininterruptregister]orpollthefindcontrol

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

information is placed in the registers. If FOUND is not set, an address was not found and the rest of the

lookup table is empty.

The FINDNEXT command finds the next address from that contained in the findnode register or the same

address on a separate VLAN. The user can either write a value in findnode and findVLANID and find the next

address or keep the current value and continue finding next addresses. The procedure for the FIND command

is as follows:

• Write the starting address in findnode and findVLANID (if desired) or keep the currently held address

and VLAN.

• Set the NEXT bit in findcontrol. The TNETX15VE scans the lookup table for the next address after the

one contained in findnode or for the same address in a separate VLAN. The search is confined to a

VLAN and/or PORT by setting those bits in the findcontrol register.

• Wait until the FNDCPLT interrupt is asserted. [FNDCPLT (bit 6) in interrupt register] or poll the

findcontrol register until the NEXT bit is cleared.

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

information is placed in the registers. If FOUND is not set, and an address was not found, the rest of the

lookup table is empty.

The commands can be combined to quickly dump the address table. All that is required is a FINDFIRST followed

by FINDNEXT commands, until no more addresses are found.

Due to the TNETX15VE efficiency in adding addresses and changing ports, and since these functions occur

without user intervention, a method is necessary to keep the host informed of all addresses that have changed.

The interrupt registers fulfill this function, but during the time that one interrupt is processed, many more can

go by unnoticed. The management is then reduced to scanning in the table using the FIND logic operation to

determine which addresses have changed. This is impractical in that a local copy of the table must be kept and

then compared with the TNETX15VE table. To alleviate this problem, the NEW flag is used.

The NEW flag in the SRAM is asserted every time the TNETX15VE adds an address or changes an address

port assignment. The FIND logic operation, tuned to look for this flag in the SRAM, filters out addresses that

have not changed.

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