RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
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 MAX_INSERT and R_MAX_BUF are configured such that inserting the
maximum number of cells into a buffer which is near it’s R_MAX_BUF limit will
cause the number of frames in the buffer to exceed 1FE, the “Robust SN
Algorithm” may cause overruns due to misinserted cells and failure of the SN
error protection mechanism. This will occur when a cell arrives which causes the
SN processing to go to the OUT OF SEQUENCE state and the buffer is too full
to allow the cell to be treated as a lost cell and stored as if cells had been lost.
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:
• 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 mismatches.
• No signaling information will be updated until a valid and correct
pointer is received.
If the DISABLE_SN bit in the R_SN_CONFIG receive queue table memory
register (refer to “DISABLE_SN” on page 228) is set, then both the Fast and
Robust Sequence Number Processing algorithms are disabled.. That is, RALP
will neither insert nor drop cells due to sequence number errors, but will update
both the R_INCORRECT_SN and R_INCORRECT_SNP counters.
If R_AAL0_MODE bit is set in the R_MP_CONFIG register then no SN
processing is done and byte six of the cell is handled as a data byte.
9.2.2.2.3 Fast Sequence Number processing State Machine
The RALP sequence number processing state machine 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, in the R_SN_CONFIG receive
queue table memory register, 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.
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL
107
PMC [ PMC-SIERRA, INC ]
