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CHAPTER 5 SAR FUNCTION
209
Figure 5-46. Receive Packet Filtering Flow
Reception
Discard
Reception
Broadcast address ("all 1s")
match
No
Yes
Unicast address
match
No
Yes
Multicast address
match
(hashing)
No
Yes
Reception
Receive the first cell
<1>
Upon receiving the first cell of a packet, the
μ
PD98405 recognizes the position of the destination
address from the offset set in the MAC field of the VC table, then compares the destination address
of the receive packet with the broadcast address (that consisting of "all 1s"). If they match, the
μ
PD98405 accepts the packet.
<2>
The
μ
PD98405 compares the 6-byte unicast address in the MAU and MAL registers with the
destination address of the receive packet. If they match, the
μ
PD98405 accepts the packet. The
host must set its own MAC address (unicast address) in the MAU and MAL registers in advance.
<3>
The
μ
PD98405 checks for multicast address matching, which is based on a hash method. First, the
μ
PD98405 performs CRC-32 calculation for the destination address of the receive packet, then
makes the upper 6 bits of the calculation result valid. If those bits of the HTU and HTL registers
which correspond to the value in these 6 bits are set to 1, the
μ
PD98405 accepts the packet. If these
bits of the HTU and HTL registers are instead set to 0, the
μ
PD98405 discards all cells, up to the last
one, that belong to that packet. An example of using the hash method is shown below: