PRELIMINARY
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
The EPP is logically split up into an input/ingress EPP (iEPP) and an output/egress EPP (oEPP). The LCS
Grant Manager sends grants for input queues which have some space left, and arbitrates among
competing flows. The Grant Matching logic matches incoming cell bodies with their LCS grant labels. The
iEPP Tag Information Base (iTIB) is a table of multicast port fanouts indexed by LCS multicast tags. The
TDM Frame Tables are indexed by TDM slot and contain scheduling information. The Scheduler Request
Modulator provides OC-48c granularity backpressure for unicast flows, arbitrates among competing
best-effort flows, and restores OC-48c granularity to port-granularity grants from the Scheduler chip. The
Output Scheduler block arbitrates among all egress flows to determine which flow may send a cell to the
linecard each cell time.
The following section describes cell flows within the EPP. The remaining sections describe the blocks of
the EPP in more detail.
3.1.1 EPP Data Flows
3.1.1.1 iEPP Cell Arrival: LCS Request-Grant-Cell Flow
The EPP uses the LCS, version 2 (Linecard-to-Switch) protocol. This is a major enhancement to the
original LCS protocol in that requests from the linecard are separated from their cell body, reducing the
storage requirements of ETT1. The details of LCS are described elsewhere, but the basic operation is as
follows:
1. A cell arrives at the ingress linecard and is destined for some output channel, O.
2. The linecard issues a request to the EPP, indicating the output queue (O). The cell body is not sent
to the EPP at this time.
3. The EPP returns a grant to the linecard, indicating that the cell body can now be forwarded to the
switch. This grant is also an implicit credit, so that the linecard can issue a further request for this
output (O).
The input Dataslices, iDS0, iDS1 and iDS2, send their input request and cell data to the input EPP on
d2p_d0_id[7:0], d2p_d1_id[7:0], d2p_d2_id[7:0], respectively. The LCS ingress header and first 10 bytes of
cell payload are sent. The request portion of the LCS ingress header goes to the LCS Grant Manager,
which arbitrates among all flows with requests (and space in the input queues) to choose the flow which
will receive the next grant. The LCS Grant Manager sends the grant label and sequence number back to
input Dataslice 0 via p2d_d0_id[7:0].
If the grant is unicast, its label information is put into a programmable delay line to the Scheduler Request
Modulator. This allows requests to be sent to the Scheduler before the arrival of unicast cell bodies. The
delay is programmed so that Scheduler grants will not come back before the arrival of the cell bodies,
providing that the system round trip time constraint (64 celltimes) is met.
The LCS Grant Manager also sends the grant label and sequence number to the Grant Matching block,
which matches incoming cell sequence numbers with previously stored grant sequence numbers, and
restores the associated label information to the cell whose payload has just arrived. When a match is
made, several things happen:
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PMC [ PMC-SIERRA, INC ]
