CDK8920A View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
'CDK8920A' PDF : 144 Pages View PDF
CS8920A
IAHashA
0
1
0
0
X
PromiscuousA
0
0
0
0
1
MulticastA
0
0
1
0
X
IndividualA
1
0
0
0
X
BroadcastA
0
0
0
1
X
Frames Accepted
Individual Address frames
with DA matching the IA at
PacketPage base + 0158h
Individual Address frames
with DA that pass the hash
filter (DA[0] must be 0)
Multicast frames with DA that
pass the hash filter (DA[0]
must be 1)
Broadcast frames
All frames
Table 5.6. Configuration Options for DA filtering
It may become necessary for the host to change asserting one of the decoder’s outputs. The as-
the Destination Address (DA) filter criteria with- serted output is compared with a corresponding
out resetting the CS8920A. This can be done as bit in the 64-bit Logical Address Filter, located at
follows:
PacketPage base + 0150h. If the decoder output
and the Logical Address Filter bit match, the
1. Clear SerRxON (Register 13, LineCTL, Bit 6) frame passes the hash filter and the Hashed bit
to prevent any additional receive frames while (Register 4, RxEvent, Bit 9) is set. If the two do
the filter is being changed.
not match, the frame fails the filter and the
Hashed bit is clear.
2. Modify the DA filter bits (B, A, 9, 7, and 6) in
the RxCTL register. Modify the Logical Ad- Whenever the hash filter is passed by a "good"
dress Filter at PacketPage base + 0150h, if frame, the RxOK bit (Register 4, RxEvent, Bit 8)
necessary. Modify the Individual Address at is set and the bits in the HR are mapped to the
PacketPage base + 0158h, if necessary.
Hash Table Index bits (Register 4, RxEvent, Bits
A through F).
3. Set SerRxON to re-enable the receiver.
Broadcast Frame Hashing Exception
Because the receiver has been disabled, the
CS8920A will ignore frames while the host is Table 5.7 describes in detail the content of the
changing the DA filter.
RxEvent register for each output of the hash and
address filters and describes an exception to nor-
Hash Filter
mal processing. That exception can occur when
the hash-filter Broadcast address matches a bit in
The hash filter is used to help determine which the Logical Address Filter. To properly account
Multicast frames and which Individual Address for this exception, the software driver should use
frames should be accepted by the CS8920A.
the following test to determine if the RxEvent
register contains a normal RxEvent (meaning bits
Hash Filter Operation: See Figure 5.5. The DA E-A are used for Extradata, Runt, CRC Error,
of the incoming frame is passed through the Broadcast and IndividualAdr) or a hash-table
CRC logic, generating a 32-bit CRC value. The RxEvent (meaning bits F-A contain the Hash Ta-
six most-significant bits of the CRC are latched ble Index).
into the 6-bit hash register (HR). The contents of
the HR are passed through a 6-to-64-bit decoder,
96
DS238PP2
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