PM73121ꢀAAL1gator II
Data Sheet
PMC-Sierra, Inc.
PMC-980620
,VVXHꢀꢁ
AAL1 SAR Processor
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If the line is in SDF-MF mode and R_CHAN_NO_SIG = 1 in the R_MAX_BUF word
(refer to “R_MAX_BUF Word Format” on page 157), then the queue is handled as if it is
in SDF-FR mode. The structure should be adjusted from a multiframe structure to a frame
structure. For example, a channel with two DS0s would have a structure size of two bytes
when R_CHAN_NO_SIG is set and a structure size of 49 bytes (include two signaling
nibbles) if in T1 mode when R_CHAN_NO_SIG is off.
3.6.2 Underrun
The AAL1gator II declares an underrun condition for a VC when no data is present in the VC
receive buffer. When this situation occurs, the AAL1gator II plays out conditioned data and old
signaling from multiframe 0 onto the timeslots assigned to the VC experiencing underrun.
Timeslots generated by other VCs are unaffected. Each time a cell is received after a queue has
entered an underrun condition, the UNDERRUN sticky bit is set. RALP does not know about an
underrun until a cell is received for the queue that underflowed. To make sure that each underrun
is counted only once, RALP will increment the R_UNDERRUN counter when exiting the under-
run state and entering the resume state. The initial underrun caused by reset is not counted. Forced
underruns due to other errors are not counted by the underrun counter. If the underrun counter is
read and the queue is currently in underrun, the present underrun condition will not be accounted
for until the queue exits underrun. To determine if the queue is in underrun, check the level of
the R_UNDERRUN bit in the R_LINE_STATE register. When not in UDF-HS mode, the
choice of conditioning data and signaling while in underrun depends on the value of RX_COND
in the R_CH_QUEUE_TBL. Three choices exist:
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Play out the data from R_COND_DATA and the signaling from multiframe 0 (Default).
Play out pseudorandom data and the signaling from multiframe 0. (For applications that
are sensitive to constant data.) The pseudorandom data option uses the data from R_
COND_DATA and then replaces the most significant bit with the result of an 18th order
18
7
polynomial, specifically x + x + 1.
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Play out old data and the signaling from multiframe 0. (Also for applications that are
sensitive to constant data.) The old data option replays out the contents of the data in the
receive buffer for that channel. Data is played out from the location of the read pointer.
Therefore, the oldest data is played out first.
If in UDF-HS mode and in underrun, the data played out is the conditioned data defined for line 0,
channel 0. There is no old data or pseudorandom data options available for UDF-HS mode.
If the data is structured, the RALP searches for a new pointer, and finds the start of the structure.
In all cases the RALP queues up data for one CDVT worth of time before exiting the underrun
condition. The R_UNDERRUN bit in R_LINE_STATE word of R_QUEUE_TBL indicates if the
queue is in an underrun state. The UNDERRUN sticky bit is set each time a cell is received during
the underrun condition. Cells received while the pointer and start of structure are being located are
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PMC [ PMC-SIERRA, INC ]
