PM73121ꢀAAL1gator II
Data Sheet
PMC-Sierra, Inc.
PMC-980620
,VVXHꢀꢁ
AAL1 SAR Processor
guarantee that the queue does not underrun in situations that could be handled by the sequence
number processing algorithm. If bit integrity is lost, then the queue will be forced into an under-
run condition and realign with the structure if one exists.
NOTE: SN processing takes place independent of whether or not a queue is in underrun. If
cells are detected lost while transitioning through an underrun state, or into a forced
underrun state, no cells will be inserted.
MAX_INSERT controls the maximum number of cells that will be inserted when cells are lost. If
more cells than MAX_INSERT are lost, then the queue will be forced into an underrun condition.
The default value of MAX_INSERT, “000”, is equivalent to “111” which means that up to seven
cells will be inserted. MAX_INSERT is in the R_SN_CONFIG register and can be specified on a
per-queue basis.
If seven cells are lost, this will appear as a misinserted cell and will not be handled correctly.
Likewise, if more than seven cells are lost, it will appear as if fewer than seven cells were lost
because the SN repeats every eight cells. If seven or more cells were lost, there is high probability
that the queue will underrun. If the queue has not underrun, the RALP takes the following steps to
minimize the impact:
1. Any time cells are inserted, if the next received pointer mismatches, it will immediately create
a forced underrun to realign to the structure instead of waiting for two consecutive mis-
matches.
2. No signaling information will be updated until a valid and correct pointer is received.
If DISABLE_SN (refer to “DISABLE_SN” on page 160) is set, no SN or SNP processing occurs.
That is, no cells will be inserted or dropped but statistics will be kept.
The RALP begins in the START state. Once a cell is received with a valid SN, the OUT_OF_
SYNC state is entered. Any cells received while in the START state, including one with a valid
SN are dropped, unless NODROP_IN_START (refer to “NODROP_IN_START” on page 161) is
set. If this bit is set and the cell has a valid SN, the cell will be accepted.
NOTE: If it is important to not dump the first cell received, make sure NODROP_IN_
START is set.
While in the OUT_OF_SYNC state, if another cell is received with a valid SN and in the correct
sequence, then the SYNC state is entered and the cell is accepted. Otherwise, if a cell with an
invalid SN is received, then the START state is re-entered and the cell is dropped. Otherwise, if
the cell has a valid SN but is in the incorrect sequence, then the cell is dropped and the RALP
remains in the OUT_OF_SYNC state.
ꢃꢈ
PMC [ PMC-SIERRA, INC ]
