PRELIMINARY
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Unicast input queues are per-priority, per-destination (port, subport). If the destination port is OC-192c, the
only valid subport is 0 and the queue length is 64 cells. If the destination port is OC-48c, there is a separate
queue per subport, 16 cells each.
Multicast input queues are per-priority and are 96 cells in length.
TDM input queues are per-subport. If this port is OC-192c, the only valid subport is 0 and the queue length
is 96. If this port is OC-48c, there is a separate queue per subport, 24 cells each. When a TDM Sync
command arrives from the Scheduler, TDM input queues are instantly emptied. If cells were present in any
TDM input queue, the “Cells Flushed by TDM Sync” interrupt is raised.
Control Packet input queues are per-subport. The length is 8 regardless of OC-48c mode. Control Packet
queues never receive grants from the Scheduler. Instead, OOB must write (any value) to the appropriate
“Linecard to OOB FIFO Subport [3:0] Status” register in order to dequeue a Control Packet cell.
If a Control Packet arrives for a full queue, an “LC2OOB/CPU CP FIFO Overflow, LC[3:0]” interrupt is
raised. If the Scheduler grants to an empty (unicast/multicast/tdm) queue, a “Scheduler Grant to Empty *
Queue” is raised. If a cell of any traffic type arrives for a full queue, the cell will be dropped (no write
command to the Dataslices). If there is a Scheduler grant to any empty queue, no cell will be transmitted
(no read command to the Dataslices).
All input queues are simple circular buffers.
3.1.5 Output Queue Manager
The Output Queue Manager stores arriving cells from the Data Crossbars, and sends/dequeues departing
cells under control of the Output Scheduler.
Unicast output queues are per-priority, per-source port, per-destination subport. If this EPP is OC-192c,
the only valid subport is 0, and the length is 64. If this EPP is OC-48c, there is a separate output queue for
each subport, and the length is 16. All unicast output queues are simple circular buffers.
Multicast output queues are per-priority, shared among output subports. When a multicast cell arrives, it is
stored at one location regardless of how many destination subports it is to be sent to. In OC-48c mode, a
separate list of queue locations is maintained for each subport, so that each subport appears to have a
different queue with up to 96 locations. Since the 96 locations are actually shared by all subports, it is
possible for congestion on one subport to back up the entire queue. If multicast backpressure is enabled,
then multicast traffic destined for other ports at the same priority may be blocked. The multicast output
queues are not simple circular buffers, instead they use a linked-list representation.
There is only one TDM output queue, length 96, shared among subports the using the same mechanism
as the multicast output queues.
There is no queue for egress Control Packets; instead, there is one allocated cell location in Dataslice
Output Queue Memory for each type of egress Control Packet. Several of these locations must be
initialized by the OOB before the switch begins to operate; see Section 3.3 “Output Dataslice Queue
Memory Allocation with EPP” for details.
160
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
PMC [ PMC-SIERRA, INC ]
