VT6516 datasheet(50/73 Pages) ETC

50 / 73 page

VIA Technologies, Inc.

Preliminary VT6516 Datarsheet

-50-

* Base Address: 1400H

Addres

(offset

)

Function

Name

Bits

Defau

Value

00H

bits of MAC address used as index for forwarding table

3’b000: use MAC address bit 10-0 (default)

3’b001: use MAC address bit 11-0

3’b010: use MAC address bit 12-0

3’b011: use MAC address bit 13-0

3’b100: use MAC address bit 14-0

others, use MAC address bit 10-0

This register specifies the lookup hash key. For example, if the

MAC address bits [14:0] is used as the hash key, there must be 32K

96-byte table entries necessary to be allocated in the upper part of

SRAM for destination MAC lookup and source MAC learning.

HASH_BITS

[2:0]

R/W

01-

03H

starting SRAM address register for forwarding table base

The forwarding table should be located above the linked buffer

entries in the SRAM. The starting address of the forwarding table is

specified by TBL_BASE in unit of 32-bit word. The occupied size is

determined by HASH_BITS. For example, if there are maximum

5461 buffers entries used for 8MB SDRAM, the minimum

forwarding table base is 5461*3 because each linked buffer entry is

of size 96 bits (3 words).

TBL_BASE

[18:0]

R/W

04H

user configured Forwarding Mode

bit 0 – if using the specified forwarding mask without lookup

(default: 0, to take lookup without specified mask)

bit 1 – if not forwarding packets destined to congested ports

(default: 0, not to filter packets by congestion factors)

If FWD_MODE[0] = 1, the incoming packets would not be

forwarded with table lookup. However, the USER_PM is used as

the forwarding mask if the incoming packets are not from the CPU

port. For broadcast & lookup-miss packets, the USER_PM is

returned by Forwarding Control to IO Control as the lookup result.

If FWD_MODE[1] = 1, the incoming packets would not be

forwarded to the congested ports whose congestion factors are larger

than 511.

FWD_MODE [1:0]

R/W

05-

07H

USER configured Port Mask

The USER_PM is used as the lookup result for the incoming packets

from Ethernet ports in the following cases:

FWD_MODE = 1

FWD_MODE = 0, VLAN is off, STP_STATE is “forward”, and this

is a broadcast packet or a lookup-miss packet

USER_PM

[16:0]

R/W

08-

09H

port mask for packets sent by CPU

The CPU_PM is used as the lookup result for the incoming packets

from the CPU port without regard to packet’s DMAC.

CPU_PM

[15:0]

R/W

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