calculation and insertion in the transmit path, and error detection in the receive path. Supported offloading
types:
• Transmit IP header checksum
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• Transmit TCP/UDP/ICMP checksum
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• Receive IP header checksum
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• Receive full checksum
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Frame Filtering
The EMAC implements the following types of filtering for receive frames.
Source Address or Destination Address Filtering
The Address Filtering Module checks the destination and source address field of each incoming packet.
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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.
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In hash filtering mode, the filter performs imperfect filtering for unicast addresses using a 64-bit hash table.
It uses the upper six 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.
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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 64-bit hash table. For
hash filtering, it uses the upper six 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.
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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.
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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.
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Ethernet Media Access Controller
Altera Corporation
cv_54017
Frame Filtering
17-20
2013.12.30