LAN9215-MT datasheet(29/144 Pages) SMSC

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16-bit Non-PCI 10/100 Ethernet Controller with HP Auto-MDIX Support

Datasheet

SMSC LAN9215

Revision 2.9 (03-01-12)

DATASHEET

3.4

Filtering Modes

3.4.1

Perfect Filtering

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

value programmed into the MAC Address High register and the MAC address low register. The MAC

address is formed by the concatenation of the above two registers in the MAC CSR Function.

3.4.2

Hash Only Filtering

This type of filtering checks for incoming Receive packets with either multicast or physical destination

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

During imperfect hash filtering, the destination address in the incoming frame is passed through the

CRC logic and the upper six bits of the CRC register are used to index the contents of the hash table.

The hash table is formed by merging the register’s multicast hash table high and multicast hash table

low in the MAC CSR Function to form a 64-bit hash table. The most significant bit determines the

of 00000 selects Bit 0 of the multicast hash table low register and a value of 11111 selects Bit 31 of

the multicast hash table high register.

3.4.2.1

Hash Perfect Filtering

In hash perfect filtering, if the received frame is a physical address, the LAN9215 Packet Filter block

perfect-filters the incoming frame’s destination field with the value programmed into the MAC Address

High register and the MAC Address Low register. If the incoming frame is a multicast frame, however,

the LAN9215 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 the

“Hash Only Filtering” section above.

3.4.2.2

Inverse Filtering

In inverse filtering, the Packet Filter Block accepts incoming frames with a destination address not

matching the perfect address (i.e., the value programmed into the MAC Address High register and the

MAC Address Low register in the CRC block and rejects frames with destination addresses matching

the perfect address).

For all filtering modes, when the MCPAS bit is set, all multicast frames are accepted. When the PRMS

bit is set, all frames are accepted regardless of their destination address. This includes all broadcast

frames as well.

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

Table 3.1 Address Filtering Modes (continued)

MCPAS

PRMS

INVFILT

HPFILT

DESCRIPTION

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