Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface

Datasheet

Table 3.13 Address Filtering Modes (continued)

MCPAS

PRMS

INVFILT

HFILT

HPFILT

DESCRIPTION

 

 

 

 

 

 

1

0

0

0

X

Pass all multicast frames. Frames

 

 

 

 

 

with physical addresses are

 

 

 

 

 

perfect-filtered

 

 

 

 

 

 

1

0

0

1

1

Pass all multicast frames. Frames

 

 

 

 

 

with physical addresses are hash-

 

 

 

 

 

filtered

 

 

 

 

 

 

3.5.3.1Perfect Filtering

This filtering mode passes only incoming frames whose destination address field exactly matches the value programmed into the MAC address high register (refer to Section 4.4.2, "MAC Address High Register (ADDRH)," on page 123) and the MAC address low register (refer to Section 4.4.3, "MAC Address Low Register (ADDRL)," on page 124). The MAC address is formed by the concatenation of the above two registers in the MCSR.

3.5.3.2Hash Only Filtering Mode

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 concatenating the register’s multicast hash table high (refer to Section 4.4.4, "Multicast Hash Table High Register (HASHH)," on page 125) and multicast hash table low (refer to Section 4.4.5, "Multicast Hash Table Low Register (HASHL)," on page 126) in the MCSR to form a 64-bit hash table. The most significant bit of the CRC determines the register to be used (High/Low), while the other five bits determine the bit within the register. A value 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.

3.5.3.3Hash Perfect Filtering

In hash perfect filtering, if the received frame is a physical address, the packet filter block perfect-filters the incoming frame’s destination field with the value programmed into the MAC Address High register (refer to Section 4.4.2, "MAC Address High Register (ADDRH)," on page 123) and the MAC address low register (refer to Section 4.4.3, "MAC Address Low Register (ADDRL)," on page 124). If the incoming frame is a multicast frame, however, the 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 3.5.3.2.

3.5.3.4Inverse Filtering

During 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 MCPAS 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.

Revision 1.22 (09-25-08)

56

SMSC LAN9420/LAN9420i

 

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