PM7344 datasheet(71/293 Pages) PMC

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PM7344 S/UNI-MPH

DATA SHEET

PMC-950449

ISSUE 6

MULTI-PHY USER NETWORK INTERFACE

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

9.16

Receive ATM Cell Processor (RXCP)

The Receive ATM Cell Processor (RXCP) Block integrates circuitry to support

cell delineation, cell payload descrambling, header check sequence (HCS)

verification and idle/unassigned cell filtering.

The RXCP cell delineates the framed T1 or E1 cell streams. Overhead bits (the

framing bit for T1 interfaces, or timeslots 0 and 16 for E1 interfaces) are

indicated by the FRMR block. Overhead bits in arbitrary rate interfaces are

indicated by the ROHM input.

Cell delineation is the process of framing to ATM cell boundaries using the

header check sequence (HCS) field found in the ATM cell header. The HCS is a

CRC-8 calculation over the first 4 octets of the ATM cell header. When

performing delineation, correct HCS calculations are assumed to indicate cell

boundaries.

The RXCP performs a sequential bit by bit hunt for a correct HCS sequence.

While performing this hunt, the cell delineation state machine is in the HUNT

state. When a correct HCS is found, the RXCP locks on the particular cell

boundary and enters the PRESYNC state. This state verifies that the previously

detected HCS pattern was not a false indication. If the HCS pattern was a false

indication then an incorrect HCS should be received within the next DELTA cells.

At that point a transition back to the HUNT state is executed. If an incorrect HCS

is not found in the PRESYNC state then a transition to the SYNC state is made.

In this state synchronization is not relinquished until ALPHA consecutive incorrect

HCS patterns are found. In such an event a transition is made back to the

HUNT state. The state diagram of the cell delineation process is shown in Figure

15.

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