Freescale Semiconductor MPC8260 - Manual (Page 1184)

ATM Transmission Convergence Layer
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
34-6 Freescale Semiconductor
Figure 34-4. 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.
34.2.1.1 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.
34.2.2 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 x
43
+ 1.
The HEC is generated using the polynomial x
8
+ x
2
+ x + 1. The coset polynomial x
6
+ x
4
+ x
2
+ 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).
34.2.2.1 Transmit ATM 2-Cell FIFO
The transmit FIFO provides FIFO management and an interface to the UTOPIA transmit interface. The
FIFO provides the cell rate decoupling between the transmission system physical layer and the ATM layer.
Detection Correction
Multi-bit error
Mode Mode
detected
(Cell discarded)
No error detected
(correction)
Single-bit error detected
Error detected
(Cell discarded)
No error detected
(No action)