CS8900A-CQZ View Datasheet(PDF) - Cirrus Logic

Part Name

Description

Manufacturer

CS8900A-CQZ

Crystal LAN™ Ethernet Controller

Cirrus Logic 

CS8900A

Crystal LAN™ Ethernet Controller

5.2.13 Broadcast Frame Hashing Excep-

tion

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-

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).

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

Frame

Passes

Hash

Filter?

Contents of RxEvent

Bits F-A

Bit 9

Hashed

Individual no

Address no

yes

Hash Table Index

1

no ExtraData Runt CRC Error Broadcast Individual Adr 0

yes don’t care ExtraData Runt CRC Error Broadcast Individual Adr 0

Multicast no

Address no

yes

Hash table index

1

no ExtraData Runt CRC Error Broadcast Individual Adr 0

yes don’t care ExtraData Runt CRC Error Broadcast Individual Adr 0

Bit 8

RxOK

1

1

0

1

1

0

Bit 6

IAHash

1

0

0

0

0

0

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

Destination Address (DA)

from incoming frame

CS8900A

CRC

Logic

(MSB) 32-bit CRC value (LSB)

6-bit Hash Register (HR)

[Hash Table Index]

to

Hashed

1

bit

64-input

OR gate

6-to-64 decoder

64

64-bit Logical Address Filter (LAF)

Written into PacketPage base + 150h

Figure 23. Hash Filter Operation

CIRRUS LOGIC PRODUCT DATASHEET

DS271F4

89

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