CS89712 datasheet(58/170 Pages) CIRRUS

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CS89712

DS502PP2

4) Normal Interrupt Generation.

Figure 20 diagrams frame pre-processing.

2.32.3.1

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 2.32.7, “Receive

Ethernet Port Locations” for a more detailed de-

scription of DA filtering.

2.32.3.2

Early Interrupt Generation

The Ethernet port supports the following two early

interrupts for frame reception.

•

RxDest

The RxDest bit (bit F of BufEvent register) is

set as soon as the Destination Address (DA) of

the incoming frame passes the DA filter. If the

RxDestiE bit (BufCFG register bit F) is set, the

CS89712 generates a corresponding interrupt.

Once RxDest is set, the software is allowed to

read the incoming frame's DA (the first 6 bytes

of the frame).

•

Rx128

The Rx128 bit (BufEvent register bit B) is set

as soon as the first 128 bytes of the incoming

frame have been received. If the Rx128iE bit

(BufCFG register bit B) is set, the CS89712

generates a corresponding interrupt. Once the

Rx128 bit is set, the RxDest bit is cleared and

the software is allowed to read the first 128

bytes of the incoming frame. The Rx128 bit is

cleared by the software reading the BufEvent

Status Queue) or by the CS89712 detecting the

incoming frame’s End-of-Frame (EOF) se-

quence.

Like all Event bits, RxDest and Rx128 are set by

the whenever the appropriate event occurs. Unlike

other Event bits, RxDest and Rx128 may be cleared

Pass

DA Filter?

Discard Frame

Destination

Address Filter

Check:

- PromiscuousA?

- IAHashA?

- MulticastA?

- IndividualA?

- BroadcastA?

Receive Frame

Yes

Generate Interrupts

Check:

- RxOKiE?

- ExtradataiE?

- CRCerroriE?

- RuntiE?

Pre-Processing

Complete

Generate Early

Interrupts if Enabled

(see next figure)

Acceptance Filter

Check:

- RxOKA?

- ExtradataA?

- RuntA?

- CRCerrorA?

Status of receive

frame reported in

RxEvent register,

frame discarded.

Status of receive

frame reported in

RxEvent register,

frame accepted

into on-chip RAM

Pass

Accept.

Filter?

Figure 20. Receive Frame Pre-Processing

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