MPC8280 datasheet(1221/1386 Pages) FREESCALE

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ATM Transmission Convergence Layer

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

35-5

When the cell delineation state machine is in the SYNCH state, the HEC verification state machine

(see Figure 35-4) implements the correction algorithm. This state machine makes sure that a single cell

header is corrected at a time. If consecutive cells are detected with single bit errors in their headers, only

the first cell error is corrected and the rest are discarded. This state machine reduces the probability of the

delivery of cells with errored headers under bursty error conditions.

Figure 35-4. HEC: Receiver Modes of Operation

The RCF can also perform idle/unassigned cell filtering. Both features are programmable

(TCMODE[CF]). Cells that are detected to be idle/unassigned are discarded, that is, not forwarded to the

UTOPIA interface Rx FIFO.

35.2.1.1

Receive ATM 2-Cell FIFO

The receive FIFO provides FIFO management and an interface to the UTOPIA receive cell interface. The

receive FIFO can hold two ATM cells, thereby providing the cell rate decoupling function between the

transmission system physical layer and the ATM layer.

FIFO management includes filling the FIFO, indicating to the UTOPIA interface that it contains cells,

maintaining the FIFO read and write pointers, and detecting FIFO overrun (TCER[OR]) conditions.

35.2.2

Transmit ATM Cell Functions

The transmit ATM cell functions block (TCF) performs the ATM cell payload scrambling and is

responsible for the HEC generation and the idle cell generation.

The TCF scrambles (programmable by the user) the cell payload using the self-synchronizing scrambler

with polynomial x43 + 1.

The HEC is generated using the polynomial x8 + x2 + x + 1. The coset polynomial x6 +x4 +x2 + 1 is added

(modulo 2) (programmable by the user) to the calculated HEC octet. The result overwrites the HEC octet

on the transmitted cell. When the transmit FIFO is empty, the TCF inserts idle cells (counted in ICC).

The TCF accumulates the number of transmitted assigned cells in a counter (TCC).

Detection

Correction

Multi-bit error

Mode

detected

(Cell discarded)

No error detected

(correction)

Single-bit error detected

Error detected

(Cell discarded)

No error detected

(No action)

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