Freescale Semiconductor MPC8260 Benutzerhandbuch

34-4

Freescale Semiconductor

 

The ATM receive cell functions block (RCF) performs the receive functions of the TC block. It performs 
cell delineation, cell payload descrambling, HEC verification and correction, and idle/unassigned cell 
filtering.

Cell delineation is the process of framing data to ATM cell boundaries using the header error check (HEC) 
received in the ATM cell header. The HEC is a CRC-8 calculation over the first four octets of the ATM 
cell header. The cell delineation algorithm assumes that repetitive correct HEC calculations over 
consecutive cells indicate valid ATM cell boundaries.

The RCF performs a sequential bit by bit hunt for a correct HEC sequence. While performing this hunt, 
the cell delineation state machine is in HUNT state. When a correct HEC is found, the RCF locks on the 
particular cell boundary and enters the PRESYNCH state, which indicates that the previously detected 
HEC pattern is not a false indication. If a correct HEC pattern is false, an incorrect HEC is received within 
the next DELTA cells. If an incorrect cell is detected, then a transition to the HUNT state is made. If an 
incorrect HEC is not detected in the PRESYNCH state, a transition to the SYNCH state is made. In the 

SI

PowerQUICC II

TC Layer

PHY

Rx Cell

Functions

• cell delineation
• descrambling
• coset
• HEC error 

correction

Tx UTOPIA I/F

Rx UTOPIA I/F

(PHY)

(PHY)

Tx Serial I/F

Rx Serial I/F

Counters

Registers

FCC2

one channel

Rx

Tx

60x Bus

UTOPIA

Rx I/F

UTOPIA

Tx I/F

M-PHY

M-PHY

detection and 

Rx FIFO

Tx FIFO

Tx Cell

Functions

• HEC generation
• scrambling
• coset
• rate adaptation