Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Each ETT1 port is attached to one or more linecards. The port contains the shallow cell queues and
implements the LCS protocol. The port and Scheduler exchange information about cells that are waiting to
be forwarded through the Crossbar core.
The Scheduler maintains local information on the number of cells that are waiting in all of the ingress and
egress queues. It arbitrates amongst all cells in the ingress queues, and instructs all of the ports as to
which cell they can forward through the Crossbar at each cell time.
Two Crossbars are used. The first, referred to as simply ‘the Crossbar’, interconnects all of the ports with
all of the other ports, enabling cells to be forwarded from the ingress port queues to the egress port queues
(in a different port). The Crossbar is reconfigured at every cell time to provide any non-blocking one-to-one
or one-to-many mapping from input ports to output ports. Each Crossbar port receives its configuration
information from its attached port; the Crossbars do not communicate directly with the Scheduler. The
second Crossbar is the flow-control Crossbar. It passes output queue occupancy information from every
egress port to every ingress port. The ingress ports use this information to determine when requests
should and should not be made to the Scheduler.
The CPU/clock provides clocks and cell boundary information to every ETT1 device. It also has a local
CPU which can read and write state information in every ETT1 device via the OOB bus. The CPU/clock
entity is a necessary element of the ETT1 switch core, but does not contain any of the ETT1 devices.
1.2.2 Basic Cell Flow
The ETT1 Chip Set consists of four devices. Their names (abbreviations) are:
•
•
•
•
Dataslice (DS)
Enhanced Port Processor (EPP)
Scheduler (Sched)
Crossbar (Xbar)
This section describes how cells flow through these four devices.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
19
PMC [ PMC-SIERRA, INC ]
