CS8900A
Crystal LAN™ Ethernet Controller
5.2.13 Broadcast Frame Hashing Excep-
tion
termine if the RxEvent register contains a
normal RxEvent (meaning bits E-A are used
for Extra data, Runt, CRC Error, Broadcast
and IndividualAdr) or a hash-table RxEvent
(meaning bits F-A contain the Hash Table In-
dex).
Table 26 describes in detail the content of the
RxEvent register for each output of the hash
and address filters, and describes an excep-
tion to normal processing. That exception can
occur when the hash-filter Broadcast address
matches a bit in the Logical Address Filter. To
properly account for this exception, the soft-
ware driver should use the following test to de-
If bit Hashed =0, or bit RxOK=0, or (bits F-A =
02h and the destination address is all ones)
then RxEvent contains a normal RxEvent, else
RxEvent contained a hash RxEvent.
Address Erred
Type of Frame?
Received
Passes
Hash
Filter?
Contents of RxEvent
Bits F-A
Bit 9
Bit 8
Bit 6
Hashed RxOK IAHash
Frame
Individual
Address
no
no
yes
no
Hash Table Index
1
0
0
1
0
0
1
1
0
1
1
0
1
0
0
0
0
0
ExtraData Runt CRC Error Broadcast Individual Adr
yes
no
don’t care ExtraData Runt CRC Error Broadcast Individual Adr
Multicast
Address
yes
no
Hash table index
no
ExtraData Runt CRC Error Broadcast Individual Adr
yes
don’t care ExtraData Runt CRC Error Broadcast Individual Adr
Notes: 6. Broadcast frames are accepted as Multicast frames if and only if all the following conditions are met
simultaneously:
a) the Logical Address Filter is programmed as: (MSB) 0000 8000 0000 0000h (LSB). Note that this
LAF value corresponds to a Multicast Addresses of both all 1s and 03-00-00-00-00-01.
b) the Rx Control Register (register 5) is programmed to accept IndividualA, MulticastA, RxOK-only,
and the following address filters were enabled: IAHashA and BroadcastA.
7. NOT (Note 1).
Table 26. Contents of RxEvent Upon Various Conditions
(MSB)
32-bit CRC value
(LSB)
Destination Address (DA)
from incoming frame
CS8900A
CRC
Logic
6-bit Hash Register (HR)
[Hash Table Index]
6-to-64 decoder
to
Hashed
bit
1
64
64-input
OR gate
64-bit Logical Address Filter (LAF)
Written into PacketPage base + 150h
Figure 23. Hash Filter Operation
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