RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
consisting of all 24 (T1) or 32 (E1) queues configured identically as single DS0
with no pointer, full cells, and no CAS connections which will be scheduled to
build cells during frame 0, 47, 94, 13, etc.. The reference value increments by
47 frames every time the current t_data_buffer frame write pointer is equal to the
current reference value. When the microprocessor wants to add a queue, it
writes the queue number and an offset to the ADDQ_FIFO. This offset is then
added to the current reference value, and the first cell is scheduled in the
resulting frame. For example, if two single DS0 queues are scheduled one right
after the other with offsets of 0 and 1 respectively, there will never be any
clumping because the first queue will be scheduled during frames 0, 47, 94, 13,
etc, and the second queue will be scheduled during frames 1, 48, 95, 14, etc..
Note that the reference value is optimized to the configuration consisting of all 24
(T1) or 32 (E1) queues configured identically as single DS0 with no pointer, full
cells, and no CAS. This is the configuration that is most likely to experience
clumping. By using the offset field, cells can be prevented from being scheduled
within the same frame even if queues were added some time ago. Software can
guarantee this by assigning an offset equal to queue number(4:0), or by keeping
track of which offsets are available. For non-single DS0 queues, the offset is
beneficial for initial offsets if all queues have the same configuration, but won’t
guarantee that a newly added queue won’t overlap with a queue started some
time ago. However, for non-single DS0 queues, there are less queues active per
line, and therefore clumping is less of an issue.
In multiframe mode (SDF-MF), the REF_VAL_ENABLE bit should be set only for
lines which have all queues configured identically as single DS0 queues with full
cells. When enabled, the reference value is based upon a configuration
consisting of all 24 (T1) or 32 (E1) queues configured identically as single DS0
full cells with CAS. The reference value increments by 45 frames for T1
connections, and for E1 connections the reference value increments by either 44
frames or 45 frames to give an average of 44 2/17ths frames. By using different
offsets, clumping can be minimized, but not completely avoided as in the frame
mode (SDF-FR) description above. However, when using offsets, generation of
a 0 pointer cannot be guaranteed, because cells may start on non-MF
boundaries.
In order to guarantee a zero pointer for single DS0 SDF-MF connections as well
as all non-single DS0 SDF-MF connections, REF_VAL_ENABLE should be
disabled and the offset field used should be set equal to the
FRAMES_PER_CELL field in the QUEUE_CONFIG word of the Transmit Queue
Table. This will add the queue in the frame which is FRAMES_PER_CELL past
frame number 0. Note that doing this will cause all queues, that have the same
FRAMES_PER_CELL value, that are added at the same time, to be scheduled in
the same frame. To avoid the clumping of cells, Add-Queue operations can be
spread out in time so that not all queues are added at the same time.
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