SMC Networks SMC91C95 Manuel d'utilisateur télécharger pdf (Page 65)

I/O SPACE - BANK 3

OFFSET NAME TYPE SYMBOL

0 THROUGH 7 MULTICAST TABLE READ/WRITE MT

LOW

BYTE

MULTICAST TABLE 0

0 0 0 0 0 0 0 0

HIGH

BYTE

MULTICAST TABLE 1

0 0 0 0 0 0 0 0

LOW

BYTE

MULTICAST TABLE 2

0 0 0 0 0 0 0 0

HIGH

BYTE

MULTICAST TABLE 3

0 0 0 0 0 0 0 0

LOW

BYTE

MULTICAST TABLE 4

0 0 0 0 0 0 0 0

HIGH

BYTE

MULTICAST TABLE 5

0 0 0 0 0 0 0 0

LOW

BYTE

MULTICAST TABLE 6

0 0 0 0 0 0 0 0

HIGH

BYTE

MULTICAST TABLE 7

0 0 0 0 0 0 0 0

The 64 bit multicast table is used for group address

filtering. The hash value is defined as the six most

significant bits of the CRC of the destination

addresses. The three msb's determine the register

to be used (MT0-MT7), while the other three

determine the bit within the register. If the

appropriate bit in the table is set, the packet is

received. If the ALMUL bit in the RCR register is

set, all multicast addresses are received

regardless of the multicast table values.

Hashing is only a partial group addressing filtering

scheme, but being the hash value available as part

of the receive status word, the receive routine can

reduce the search time significantly. With the

proper memory structure, the search is limited to

comparing only the multicast addresses that have

the actual hash value in question.

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SMC Networks SMC91C95 Manuel d'utilisateur Page 65

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