PM73121ꢀAAL1gator II
Data Sheet
PMC-Sierra, Inc.
PMC-980620
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AAL1 SAR Processor
If the cell is accepted, the RALP then transfers the cell to the external memory using the R_
CHAN_ALLOC fields in the R_QUEUE_TBL. Figure 32 shows this receive cell process. If a
valid cell is not received in time, the queue may enter an underrun condition.
Wait for a cell in the
receive UTOPIA FIFO.
No
Check CRC-10 and place
cell in OAM queue.
Is the cell a
data cell?
Yes
Correct SN/SNP as specified
in ITU-T Recommendation
I.363.1 (refer to Appendix B
“References” on page 203).
No
Is SNP
correct?
Able to correct
Unable to correct
Accept/drop cell as specified
in ITU-T Recommendation
I.363.1 “Fast SN Algorithm”
(refer to Appendix B
No
Drop
Is SN
correct?
“References” on page 203).
Yes
Accept
Place data and signaling in
appropriate timeslots and
update write pointers.
Figure 33. Receive Cell Processing
The CDVT value allows the receiver to be configured to store a variable amount of data for that
queue before data is emitted. This storage permits the cells to arrive with variable delays without
causing errors on the line outputs. This CDVT value is used when the first cell is received after an
underrun. The AAL1gator II also provides protection from buffer overrun and pointer misalign-
ment.
The RALP reads the ATM cell from the RUTOPIA FIFO, verifies the header, and determines the
queue to which the cell belongs. It then locates the data bytes of the cell and writes them into
frame buffers provided for that line. Receive queues exist in the external memory, and 128 kBytes
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PMC [ PMC-SIERRA, INC ]
