Freescale Semiconductor MPC8260 - Manual (Page 1182)

ATM Transmission Convergence Layer
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
34-4 Freescale Semiconductor
Figure 34-2. TC Layer Block Diagram
34.2.1 Receive ATM Cell Functions
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