SMSC LAN9311 User Manual

Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface

Revision 1.4 (08-19-08)

116

SMSC LAN9311/LAN9311i

 

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

 and the 

. The MAC address is formed by the concatenation of these

two registers.

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 

 and the 

 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.

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 

 and the 

.

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

.

0

0

0

0

0

MAC address perfect filtering only 
for all addresses.

0

0

0

0

1

MAC address perfect filtering for 
physical address and hash filtering 
for multicast addresses

0

0

0

1

1

Hash Filtering for physical and 
multicast addresses

0

0

1

0

0

Inverse Filtering

X

1

0

X

X

Promiscuous

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