PM73121ꢀAAL1gator II
Data Sheet
PMC-Sierra, Inc.
PMC-980620
,VVXHꢀꢁ
AAL1 SAR Processor
that enough data is available to build a cell for that queue.
2. The CSD circuit processes all queues from the Transmit Calendar entry starting with the low-
est queue number and proceeding to the highest. The processing steps are as follows:
a. The CSD circuit obtains the QUE_CREDITS, and subtracts the average number of credits
per cell from it. The average number of credits, AVG_SUB_VALU, is the number of
credits that will be spent sending the current cell. For structured lines, the average number
of credits per cell is 46-7/8. For unstructured lines, the average number of credits per cell
is 47.
b. Next, the CSD circuit computes the frame location for the next service by subtracting the
remaining credits from 47. It divides the result by the number of channels, NUM_CHAN,
dedicated to that queue. The result is a frame differential.
c. The CSD then adds this frame differential to the present frame location to determine the
frame number of the next frame in which the TALP can build a cell. The CSD circuit then
sets a bit in the corresponding entry in the Transmit Calendar and writes to the QUEUE_
CREDITS.
d. The CSD circuit then adds the new credits back to the credit total for the frame increment
number. The number of new credits is equal to the frame differential computed earlier,
multiplied by the number of channels for that queue. Once a queue is identified as requir-
ing service, its identity is written to the NEXT_SERV location.
e. The CSD circuit obtains the next queue for that frame and repeats steps a. through d. The
CSD circuit continues this process until there are no more active queues for that frame.
3. After servicing all the queues for that frame, the CSD circuit advances to the next active line
located in the line queue. If there are no active lines, the CSD circuit returns to the idle state to
wait for the next line to request service.
ꢂꢃ
PMC [ PMC-SIERRA, INC ]
