Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
1.4.1 Flow Control Crossbar Synchronization
The Flow Control Crossbars interconnect every EPP with every other EPP. During each cell time, the Flow
Control Crossbar sets the crosspoints such that every iEPP receives update information from one other
oEPP. Further, no two iEPPs receive the same update information from the same oEPP. In the next cell
time the crosspoints must be re-organized so that every iEPP receives update information from a different
oEPP.
The system must ensure that the Flow Control Crossbars and the EPPs are all synchronized, so that every
iEPP knows from which oEPP it is receiving information at any given time. This synchronization
information is generated by the Scheduler using the FCCSYN register to send a periodic pulse out to all
EPPs. Further, if a redundant Scheduler is used then the two Schedulers must be synchronized. This
Scheduler-to-Scheduler synchronization occurs after a Scheduler Refresh operation. Refer to Section
1.9.4 “Scheduler Refresh Procedure” on page 98.
1.5 TDM SERVICE
The TDM service enables linecards to periodically reserve bandwidth within the ETT1 core. Cells that are
switched via this service will have a fixed latency through the switch and will not be delayed due to best
effort contention for an output port. 1-in-N idle cells and egress control packets may cause temporary
delays, but these should be absorbed by the guardband and speedup.
The TDM service is implemented within the ETT1 core using:
•
•
•
dedicated queues in the ETT1 ports
a table-based reservation mechanism in the ETT1 ports
a flexible synchronization mechanism
1.5.1 TDM Queues
The linecard uses the normal LCS request-grant mechanism for TDM cells. When TDM cells arrive at an
ETT1 ingress port, they are queued in a single TDM queue which can buffer up to 96 cells. The cells are
stored in the ingress queue until their reservation time occurs, at which time they are forwarded through
the crossbar to the appropriate egress TDM queue. Given that there can be no contention for TDM cells
then a TDM queue might seem unnecessary. The queue is present so that the linecard does not need to
be closely synchronized with the ETT1 fabric.
If the port is operating in subport mode then four ingress queues are used, one for each subport. Each
ETT1 port has a single egress TDM queue, even when the port is in subport mode. The ETT1 can transmit
cells out-of-order between the subports, and so a single shared TDM queue does not cause a problem.
Figure 26 illustrates the queueing structure.
54
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
PMC [ PMC-SIERRA, INC ]
