Adaptec 1737100 Programmer Manual - Page 155
high-priority Receive Completion Queue.
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Register Descriptions byte (h) word (h) 2C0 B0 2D0 B4 2E0 B8 2F0 BC Table 7-108. Address Filtering Memory (Continued) word -> 3 2 1 Internal 463-448 Internal 479-464 Internal 495-480 Internal 511-496 0 463-448 479-464 495-480 511-496 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 RXADDRESSFILTERINGCTRL 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 RXADDRESSFILTERINGCTRL 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 HASHPRIORITYENABLE bit in the RXADDRESSCTRL 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. 7-83