VT6516 ETC, VT6516 Datasheet - Page 50

• Manufacturer Part Number: VT6516
• Description: 16/12 PORT 10/1000 ASE T/TX
• Manufacturer: ETC

* Base Address: 1400H
Addres
s
(offset
)
00H
03H
07H
09H
01-
04H
05-
08-
Function
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.
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).
user configured Forwarding Mode
bit 0 – if using the specified forwarding mask without lookup
bit 1 – if not forwarding packets destined to congested ports
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.
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
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.
VIA Technologies, Inc.
(default: 0, to take lookup without specified mask)
(default: 0, not to filter packets by congestion factors)
-50-
Preliminary VT6516 Datarsheet
Register
Name
HASH_BITS
TBL_BASE
FWD_MODE [1:0]
USER_PM
CPU_PM
Bits Defau
[2:0]
[18:0]
[16:0]
[15:0]
lt
Value
0
0
0
0
0
R/
W
R/W
R/W
R/W
R/W
R/W