Motorola MPC8260 - Manual (Page 813)

29-33 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
For AAL5 and AAL1 the extra header is taken from the Rx and Tx BDs. The transmitter
reads the extra header from the UDC TxBD and adds it to each ATM cell associated with
the current buffer. At the receive side, the extra header of the last cell in the current buffer
is written to the UDC RxBD.
For AAL0 the extra header is attached to the regular ATM cell in the buffer. The transmitter
reads the extra header and the ATM cell from the buffer. The receiver writes the extra header
and the regular ATM cell to the buffer.
29.7.1 UDC Extended Address Mode (UEAD)
For external CAM accesses, the UDC extra header can be used to supply extra routing
information; see Figure 29-20. If GMODE[UEAD] = 1, two bytes of the UDC header are
used as extensions to the ATM address and the CAM match cycle performs a double-word
access. UEAD_OFFSET in the parameter RAM determines the offset from the beginning
of the UDC extra header to the UEAD entry. The offset should be half-word aligned (even
address). See Section 29.10.1, ÒParameter RAM.Ó
29.8 ATM Layer Statistics
ATM layer statistics can be used to identify problems, such as the line-bit error rate, that
affect the UNI performance. Statistics are kept in three 16-bit wrap-around counters:
¥ UTOPIA error dropped cells countÑCounts cells discarded due to UTOPIA errors:
Rx parity errors and short or long cells.
¥ Misinserted dropped cell countÑCounts cells discarded due to address look-up
failure.
¥ CRC10 error dropped cell countÑCounts cells discarded due to CRC10 errors.
(ABR only).
Extra Header (1Ð12 Bytes)
ATM Cell Header (4 Bytes) + HEC (optional)
Payload (48 Bytes)
Figure 29-19. Format of User-Defined Cells
16-bit 4-bit 12-bit 16-bit
CAM data in Þeld: UEAD PHY addr VPI VCI
0 15 16 19 20 31 32 47
Figure 29-20. External CAM Address in UDC Extended Address Mode