RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
3. Play out old data . (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.
While in underrun, the signaling data will be frozen if signaling data was not
already conditioned.
If in UDF-HS mode and in underrun, the data played out is the conditioned data
defined for line 0 for the A1SP, channel 0 or DS3 AIS. There are no old data or
pseudorandom data options available for UDF-HS mode.
Bit integrity may be maintained through an underrun condition if at least one cell
is lost and less than 6 cells are lost if the BITI_UNDERRUN is set. In order to
detect the amount of lost cells, whenever a cell is received, the value of the line
rd_ptr is stored. When a cell is received with a SN error when the queue is in
underrun, or cell is received when the SN state machine is in the
OUT_OF_SEQUENCE state, the current value of the line rd_ptr is compared
against the stored value; if the time that has passed since the last cell was
received is less than time it should have taken to play out 6 cells worth of data on
the line (stored rd_ptr – current rd_ptr < 7 * FRAMES_PER_CELL), less than 7
cells have been lost and the new incoming cell is processed normally as if an
underrun never happened. If the new updated wrt_ptr is greater than the
read_ptr, the resume bit is set to indicate to the RFTC that the underrun
condition is ending and the end-of underrun is set at wrt_ptr. One problem is
that underun can persist for a long time. To detect this, a R_LONG_UNDERRUN
bit will be set by the RFTC whenever it detects that the rd_ptr is wrapping
(rd_ptr+64= wr_ptr and the queue is already in underrun)
To exit an underrun condition, if the BITI_UNDERRUN is not set or more than 6
cells have been lost, 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. If the data is structured, the RALP searches for a new pointer, and
finds the start of the structure. Cells received while the pointer and start of
structure are being located are dropped and the POINTER_SEARCH sticky bit is
set. The DROPPED_CELL counter is also incremented. If the underrun condition
persists, the microprocessor should set the conditioned bits to derive both the
data and the signaling from the conditioned areas. The RALP can optionally
maintain MF alignment when exiting underrun, when this is done, the new data is
written at the first multiframe boundary after the minimum CDVT buffering
requirement. This option may add more delay.
By default, in SDF-MF mode, only the CDVT value is taken into account when
determining when to play out data. This provides predictable delay but causes a
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL
124
PMC [ PMC-SIERRA, INC ]
