CX82100 Home Network Processor Data Sheet
Table 7-5 shows the format for the setup frame involving multicast address filters. Note
that one physical address filter is included in this setup frame. This is usually the address
of the node itself.
Table 7-5. Imperfect Address Filtering Setup Frame Format
Entry No.
Bytes
3:0
7:4
11:8
. . . . .
119:116
123:120
127:124
131:128
135:132
139:136
. . . . .
Bits 31:16
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
. . . . .
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
. . . . .
Bits 15:0
Hash Table Row 0
Hash Table Row 1
Hash Table Row 2
. . . . .
Hash Table Row 29
Hash Table Row 30
Hash Table Row 31
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
. . . . .
0
1
2
. . . . .
29
30
31
32
33
34
39
40
41
42
159:156
163:160
167:164
171:168
. . . . .
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
. . . . .
Physical Address (Bytes [1:0])
Physical Address (Bytes [3:2])
Physical Address (Bytes [5:4])
XXXXXXXXXXXXXXXX
. . . . .
47
191:188
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
When a 48-bit multicast address is received, the RMAC hardware uses the same CRC
algorithm to generate the corresponding CRC value. This is shown in Figure 7-9.
The most significant 9 bits (in Little-Endian mode, these are the rightmost 9 bits of the
32-bit linear shift register) of the CRC value will be used to access a hardware hash table
that has been loaded by the setup frame described above. If the hash bit is 1 (a hit), the
frame will be accepted and delivered to the host CPU. Otherwise, the frame will be
rejected.
A hit on the hash table does not necessarily mean that the multicast frame delivered to the
host is actually destined to this node. It only assures that there is a possibility that the
incoming multicast address belongs to the node. To determine if it belongs to the node,
the host software must examine the address against the list of multicast addresses to be
accepted by this node.
This filtering method is called "imperfect" because multicast frames not addressed to this
node may slip through (an invalid address may be hashed into a bit location which is
turned on by a valid address), but it still decreases the number of frames that the host can
receive.
101306C
Conexant Proprietary and Confidential Information
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