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ADM5120
Function Description
Control
•
Own bit:
– If 0, the descriptor belongs to CPU.
– If 1, the descriptor is released to WAN MAC or LAN SW, which means it
can store the incoming packet based on the buffer address. If this is done,
change the bit to 0.
•
Buffer information:
– Each descriptor can support two buffers.
– The buffer address can be any byte alignment.
– Buffer1 has length information, if packet size is over the buffer1 size, then
put the rest of the data into buffer2.
– Buffer1 address must be valid when descriptor belongs to switch.
– Buffer2 has a enable bit to control whether the address is valid or not.
– The buffer2 size must be larger than the remaining data.
– If buffer2 is disabled and buffer1 has not enough space, then the remaining
data will be dropped, and no status reported.
Status
•
Packet length: the packet length in bytes including 4-byte CRC
•
Source port: the source port of packet
•
DA status:
– 00: UC, the packet is the forwarded UC packet
– 01: MC, the packet has “1” in the LSB of first byte of DA
– 11: BC, the packet has DA=FFFFFFFFFFFF
– IP checksum fail: if 1 = the IP checksum result is error
Note:
Only checked if type = 0x0800(IP) or 0x8864(PPPoE)
•
The VLAN tagged frame status (type=0x8100)
•
Packet type:
– 00: type = 0x0800, IP
– 01: type = 0x8864, PPPoE
– 10,11
reserved
ADMtek Inc.
3-9