CS8900-CQ3 Cirrus Logic, CS8900-CQ3 Datasheet - Page 83

• Manufacturer Part Number: CS8900-CQ3
• Description: Crystal LAN ISA Ethernet Controller
• Manufacturer: Cirrus Logic

DS271PP3
5.2.3 Receive Frame Pre-Processing
The CS8900A pre-processes all receive frames us-
ing a four step process:
1) Destination Address filtering;
2) Early Interrupt Generation;
3) Acceptance filtering; and,
4) Normal Interrupt Generation.
Figure 21 provides a diagram of frame pre-process-
ing.
5.2.3.1 Destination Address Filtering
All incoming frames are passed through the Desti-
nation Address filter (DA filter). If the frame’s DA
passes the DA filter, the frame is passed on for fur-
ther pre-processing. If it fails the DA filter, the
frame is discarded. See Section 5.3 on page 87 for
a more detailed description of DA filtering.
CS8900A
Crystal LAN™ ISA Ethernet Controller
Bit
Bit
D
A
B
B
7
9
Table 22. Receive Frame Pre-Processing
AutoRX DMAE When set, Auto-Switch DMA
RxDMAonly
RxDMAsize
BufferCRC
DMABurst
Bit Name
Bit Name
StreamE
Register 17, BusCTL
Register 3, RxCFG
When set, Stream Transfer
enabled.
When set, DMA slave opera-
tion used for all receive
frames.
enabled.
When set, the received CRC
is buffered.
When set, DMA operations
hold the bus for up to approx-
imately 28 µs. When clear,
DMA operations are continu-
ous.
When set, DMA buffer size is
64 Kbytes. When clear, DMA
buffer size is 16 Kbytes.
Operation
Operation
CIRRUS LOGIC PRODUCT DATA SHEET
frame reported in
RxEvent register,
into on-chip RAM
Status of receive
frame accepted
Figure 21. Receive Frame Pre-Processing
Yes
Interrupts if Enabled
Generate Interrupts
Acceptance Filter
Check:
- PromiscuousA?
- IAHashA?
- MulticastA?
- IndividualA?
- BroadcastA?
Pre-Processing
(see next figure)
Receive Frame
Generate Early
Check:
- RxOKiE?
- ExtradataiE?
- CRCerroriE?
- RuntiE?
- RxDMAiE?
Address Filter
Check:
- RxOKA?
- ExtradataA?
- RuntA?
- CRCerrorA?
Destination
Complete
DA Filter?
Accept.
Filter?
Pass
Pass
Yes
No
No
RxEvent register,
frame reported in
Status of receive
frame discarded.
Discard Frame
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