PM7326 datasheet(79/238 Pages) PMC

79 / 238 page

PM7326 S/UNI APEX

DATA SHEET

PMC-1981224

ISSUE 6

ATM/PACKET TRAFFIC MANAGER AND SWITCH

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

interrupt the retrieval of a frame from one class to transmit a higher priority

packet/cell from another class without impacting the CRC32 calculation.

The SAR will accept another cell from the queue engine when the 14

th long word

of the transmit buffer has been read. The SAR assist transmit cell transfer

format is shown in Figure 9.

Figure 9

- SAR Assist Transmit Cell Transfer Format

Bits 31-24

Bits 23-16

Bits 15-8

Bits 7-0

SarTxData0

CRC Status

SarTxECI

SarTxData1

SarTxData2

Payload1

Payload2

Payload3

Payload4

••••••••••••••••

SarTxData13

Payload45

Payload46

Payload47

Payload 48

The SAR performs CRC32 error checking over the entire frame. The CRC32

accumulator for a class is automatically reset on frame boundaries or when a

non-user or WFQ cell is encountered (see Table 8). A CRC32 status bit is

updated as the EOM cell enters the read buffer.

The SAR performs CRC10 error checking over an OAM cell. A CRC10 status bit

is updated as the OAM cell enters the read buffer. The processor should verify

the cell type (via the cell header) when determining the validity of these status

bits.

All the CRC status bits in the buffer are updated prior to indicating data is

available. Should a CRC error be detected, the microprocessor can skip reading

the cell’s entire payload and move on to the next cell by reading the 14

th word of

the transmit buffer.

10.8.2 Receive

The receive function of the SAR has the following features:

• Single write staging buffer

• ICI (Ingress Connection Identifier) prepended to all cells

• Option to overwrite the end of a cell with AAL5 CRC32 or OAM CRC-10

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