Altera cyclone V Technical Reference page 1272

cv_5v4
2016.10.28
Unicast Destination Address Filter
Up to 128 MAC addresses for unicast perfect filtering are supported. The filter compares all 48 bits of the
received unicast address with the programmed MAC address for any match. Default MacAddr0 is always
enabled, other addresses MacAddr1–MacAddr127 are selected with an individual enable bit. For
MacAddr1–MacAddr31 addresses, you can mask each byte during comparison with the corresponding
received DA byte. This enables group address filtering for the DA. The MacAddr32-MacAddr127 addresses
do not have mask control and all six bytes of the MAC address are compared with the received six bytes of
†
DA.
In hash filtering mode, the filter performs imperfect filtering for unicast addresses using a 256-bit hash
table. It uses the upper ten bits of the CRC of the received destination address to index the content of the
hash table. A value of 0 selects Bit 0 of the selected register, and a value of 111111 binary selects Bit 63 of
the Hash Table register. If the corresponding bit is set to one, the unicast frame is said to have passed the
hash filter; otherwise, the frame has failed the hash filter.
Multicast Destination Address Filter
The MAC can be programmed to pass all multicast frames. In Perfect Filtering mode, the multicast
address is compared with the programmed MAC Destination Address registers (1–31). Group address
filtering is also supported. In hash filtering mode, the filter performs imperfect filtering using a 256-bit
hash table. For hash filtering, it uses the upper ten bits of the CRC of the received multicast address to
index the contents of the hash table. A value of 0 selects Bit 0 of the selected register and a value of 111111
binary selects Bit 63 of the Hash Table register. If the corresponding bit is set to one, then the multicast
frame is said to have passed the hash filter; otherwise, the frame has failed the hash filter.
Hash or Perfect Address Filter
The filter can be configured to pass a frame when its DA matches either the hash filter or the Perfect filter.
This configuration applies to both unicast and multicast frames.
Broadcast Address Filter
The filter does not filter any broadcast frames in the default mode. However, if the MAC is programmed to
reject all broadcast frames, the filter drops any broadcast frame.
Unicast Source Address Filter
The MAC can also perform a perfect filtering based on the source address field of the received frames.
Group filtering with SA is also supported. You can filter a group of addresses by masking one or more
bytes of the address.
Inverse Filtering Operation (Invert the Filter Match Result at Final Output)
For both Destination and Source address filtering, there is an option to invert the filter-match result at the
final output. The result of the unicast or multicast destination address filter is inverted in this mode.
Destination and Source Address Filtering Summary
The tables below summarize the destination and source address filtering based on the type of frames
received and the configuration of bits within the Mac_Frame_Filter register.
Table 17-22: Destination Address Filtering
Note: The "X" in the table represents a "don't care" term.
Ethernet Media Access Controller
Send Feedback
†
†
Unicast Destination Address Filter
†
†
†
†
17-57
†
†
Altera Corporation