Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Figure 12. The Input Request Counters
EPP
0,0
2
0,1
request
0
0,2
3
OC-48c linecard
grant
0,3
7
31,3
0
The EPP can support up to four OC-48c channels, and each channel must have its own set of request
counters for each of the 128 OC-48c output channels. Figure 13 shows the full set of counters for a single
priority.
Within the EPP an LCS Grant Manager process issues grants to the linecards in response to the received
requests. Once per cell time the LCS Grant Manager selects one request counter to grant, given that many
may qualify. A request counter qualifies to receive a grant if the counter is non-zero and if there is at least
one empty cell buffer in the VOQ that is used for cells going to that particular output. Once the LCS Grant
Manager has selected a particular VOQ, it decrements the corresponding counter and sends a grant to the
appropriate linecard.
The grant indicates a specific VOQ within the linecard. When the linecard receives the grant it does two
things. First, it sends to the EPP the cell body that is currently at the head of the granted queue. Second, it
increments a local credit counter that is used to determine whether a new request for that queue can be
sent.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
35
PMC [ PMC-SIERRA, INC ]
