SMSC LAN9312 - Manual (Page 115)

High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Datasheet
SMSC LAN9312 115 Revision 1.4 (08-19-08)
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 HO HPFILT DESCRIPTION
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