Technical information

7-83
Register Descriptions
Perfect Addresses
The AIC-6915 compares the destination address of the incoming frame against all of the
perfect addresses stored in memory. The comparison is used as one of the criteria for
accepting a frame. This is indicated by the
PerfectFilteringMode
field of the
R
X
A
DDRESS
F
ILTERING
C
TRL
register. For example, if
PerfectFilteringMode = 0
, the
destination address is compared against all of the perfect addresses stored in memory. The
frame is accepted if it matches any of these perfect addresses.
The perfect addresses are stored 16-bits to a 32-bit word. The 1st and 2nd bytes of the
network are compared to the lower 16-bits stored in word 2. The 3rd and 4th bytes are
compared to the lower 16-bits of word 1. The 5th and 6th network bytes are compared to
word 0. The high-order bits within each 16-bits are compared against the first byte (1, 3, 5).
In addition, if the bit in the
AddressPriority
field in the
R
X
A
DDRESS
F
ILTERING
C
TRL
register that corresponds to the index of the perfect match is 1, the frame is considered a
high-priority frame.
Hash Addresses
The Ethernet CRC function is applied to the destination address in the incoming frame.
This is used as an index into the hash table. The upper 9 bits of the CRC are used as an
index into a hash table. If hash addressing is enabled and the bit in the hash table is a 1,
the frame is accepted. Hash addresses can optionally be used to hash only multicast
frames or any frames. When hashing multicast frames, the VLAN address of VLAN
frames can also be verified before accepting a frame.
Hash Priorities
An additional bit corresponding to each
HASH
bit indicates the priority of any frames that
are accepted because of a hash address. If the
H
ASH
P
RIORITY
E
NABLE
bit in the
R
X
A
DDRESS
C
TRL
register is set, hash priority determination is enabled. In this case, if the
HASH PRIORITY
bit corresponding to the hash address, as well as the
HASH
bit
corresponding to the hash address, are both 1, the frame is considered high-priority. If the
queue is enabled, the completion entry for the frame is DMA-transferred to the
high-priority Receive Completion Queue.
VLAN Numbers
In VLAN mode, VLAN tagged broadcast and multicast frames have their VLAN identifier
compared against entries in the VLAN table. If the VLAN number matches, the frame is
accepted. When in VLAN mode, the adapter can belong to up to 32 VLANs. The AIC-6915
compares the VLAN number against all of the entries in the table. So, for example, if the
adapter is a member of only one VLAN, all of the entries should be the same.
The VLAN numbers are programmed into the lower 12-bits of the VLAN table words. If
the 13th bit (bit_12) is set, VLAN frames with a matching VLAN number are considered
high priority. The upper 3 bits of the VLAN identifier are ignored.
2C0 B0 Internal 463-448 463-448
2D0 B4 Internal 479-464 479-464
2E0 B8 Internal 495-480 495-480
2F0 BC Internal 511-496 511-496
Table 7-108. Address Filtering Memory (Continued)
byte (h) word (h) word -> 3 2 1 0