LAN9312 datasheet(115/458 Pages) SMSC

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High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

Datasheet

SMSC LAN9312

115

Revision 1.2 (04-08-08)

DATASHEET

9.4.1

Perfect Filtering

This filtering mode passes only incoming frames whose destination address field exactly matches the

value programmed into the Host MAC Address High Register (HMAC_ADDRH) and the Host MAC

Address Low Register (HMAC_ADDRL). The MAC address is formed by the concatenation of these

two registers.

9.4.2

Hash Only Filtering

This type of filtering checks for incoming receive packets (from switch Port 0) with either multicast or

physical destination addresses, and executes an imperfect address filtering against the hash table. The

hash table is formed by merging the values in the Host MAC Multicast Hash Table High Register

(HMAC_HASHH) and the Host MAC Multicast Hash Table Low Register (HMAC_HASHL) to form a

64-bit hash table.

During imperfect hash filtering, the upper 6-bits of the destination address of the incoming frame are

used to index the contents of the hash table. The most significant bit of the destination address

determines the register to be used (HMAC_HASHH or HMAC_HASHL), while the other five bits

determine the bit within the register. A value of 00000 selects Bit 0 of the HMAC_HASHL register and

a value of 11111 selects Bit 31 of the HMAC_HASHH register.

9.4.3

Hash Perfect Filtering

In hash perfect filtering, if the received frame is a physical address, the Host MAC packet filter will

perfect-filter the incoming frame’s destination field with the value programmed into the Host MAC

Address High Register (HMAC_ADDRH) and the Host MAC Address Low Register (HMAC_ADDRL).

However, if the incoming frame is a multicast frame, the Host MAC packet filter function performs an

imperfect address filtering against the hash table.

The imperfect filtering against the hash table is the same imperfect filtering process described in

Section 9.4.2, "Hash Only Filtering".

Table 9.1 Address Filtering Modes

MCPAS

PRMS

INVFILT

HPFILT

DESCRIPTION

MAC address perfect filtering only

for all addresses.

MAC address perfect filtering for

physical address and hash filtering

for multicast addresses

Hash Filtering for physical and

multicast addresses

Inverse Filtering

Promiscuous

Pass all multicast frames. Frames

with physical addresses are

perfect-filtered

Pass all multicast frames. Frames

with physical addresses are hash-

filtered

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