Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
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The cell’s label information is sent to the input Queue Manager, which determines where the cell
will be stored in input Dataslice queue memory. If the flow’s queue is already full, the cell is
dropped and an interrupt is asserted. Otherwise, the EPP sends a write command & write address
to all input Dataslices via p2d_d[6:0]_ic[7:0]. At the same time, the EPP sends egress cell label
information to the input Dataslices, via p2d_d0_id[7:0] and p2d_d1_id[7:0]. This information is
written into the egress cell header location of the cell.
If the cell is multicast, its tag (from the label) is used as the index into the iTIB, to look up the port
fanout. If the fanout is all-0’s, the cell is dropped. Otherwise the fanout is sent to the Scheduler
Request Modulator for arbitration with other unicast and multicast cells waiting to be requested.
3.1.1.2 iEPP Cell Departure: Scheduler Request-Grant Flow
Unicast and multicast requests to the Scheduler come from the Scheduler Request Modulator, while TDM
requests to the Scheduler come from the TDM Frames block. Requests are sent to both (redundant)
Schedulers, p2s_s[1:0].
The Scheduler Request Modulator receives unicast egress queue occupancy information from all EPPs’
Output Schedulers via the Flow Control Crossbars, f2p_[a:b][1:0]. It uses this information to decide
whether it can pass on requests to the Scheduler for cells destined for those queues. The Scheduler
Request Modulator also keeps track of subport information for each request sent to the Scheduler, and
restores the subport information to grants coming back from the Scheduler via s2p_s[1:0]. This is because
the Scheduler only supports port-granularity in its arbitration.
When subport information has been restored to a valid Scheduler grant, the grant info is sent to the Input
Queue Manager. If the specified input queue is empty, then an interrupt is asserted and no cell is sent.
Otherwise, the Input Queue Manager generates a read command and read address, sent to the input
Dataslices via p2d_d[6:0]_ic[7:0]. The input Dataslices then send the cell across the Data Crossbars.
The Scheduler also sends a reverse routing tag to the EPP, to indicate from which port this port will be
receiving the next cell. This is passed to the input Dataslices via p2d_d[6:0]_ic[7:0]. The input Dataslices
pass the tag on to the data Crossbars, to configure the Crossbar fabric.
3.1.1.3 oEPP Cell Arrival: Data Crossbar to oEPP Flow
After a cell traverses the data Crossbars, it is sent out to the output Dataslices. oDS0 and oDS1 send their
cell data to the oEPP via d2p_d0_od[7:0] and d2p_d1_od[7:0]. The Output Queue Manager determines
which output queue the cell is destined for, and generates a write command and write address for the
output Dataslices. This is sent via p2d_d[6:0]_oc[7:0]. The Output Scheduler is notified that a cell has been
added to that output queue.
If the incoming cell causes a multicast output queue to grow larger than the programmable backpressure
threshold, then backpressure is asserted to the Scheduler via p2s_s[1:0]. Optionally, queue size can be
ignored and arriving multicast cells will simply be dropped if the queue fills up.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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PMC [ PMC-SIERRA, INC ]
