PM7375-SC datasheet(62/430 Pages) PMC

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PM7375 LASAR-155

DATA SHEET

PMC-931127

ISSUE 6

LOCAL ATM SAR & PHYSICAL LAYER

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

persists for 4 ms, loss of cell delineation is asserted (LCD). LCD is removed when

no OCD condition has been detected for 4 ms.

9.3.1.1 Fig. 9.2 Cell Delineation State Diagram

HUNT

PRESYNC

SYNC

correct HEC

(byte by byte)

DELTA

consecutive

correct HECs

(cell by cell)

Incorrect HEC

(cell by cell)

ALPHA

consecutive

incorrect HECs

(cell by cell)

9.3.2 Cell Filter and HEC Verification

Cells are filtered (or dropped) based on HEC errors and/or a cell header pattern.

Cell filtering is optional and is enabled through the RACP registers. When both

filtering and HEC checking are enabled, cells are dropped if uncorrectable HEC

errors are detected, or if the corrected header contents match the pattern contained

in the RACP Match Header Pattern and RACP Match Header Mask registers. Idle

or unassigned cell filtering is accomplished by writing the appropriate cell header

pattern into the RACP Match Header Pattern and RACP Match Header Mask

registers.

The HEC is a CRC-8 calculation over the first 4 octets of the ATM cell header using

the polynomial, x8 + x2 + x + 1. The coset polynomial, x6 + x4 + x2 + 1 is optionally

added (modulo 2) to the received HEC octet before comparison with the calculated

result. While the Cell Delineation State Machine (described above) is in the SYNC

state, the HEC verification circuit implements the state machine shown below.

PM7375-SC Datasheet(PDF) 62 Page - PMC-Sierra, Inc