PM9313 datasheet(39/343 Pages) PMC

39 / 343 page

PM9311/2/3/5 ETT1™ CHIP SET

PMC-2000164

ISSUE 3

ENHANCED TT1™ SWITCH FABRIC

Released

Data Sheet

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

PMC-Sierra, Inc.

Figure 12. The Input Request Counters

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.

0,0

0,1

0,2

0,3

31,3

OC-48c linecard

request

grant

EPP

PM9313 Datasheet(PDF) 39 Page - PMC-Sierra, Inc