RELEASED
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
5
Scheduler
This chapter contains information on the Scheduler device, part number PM9311-UC, available from
PMC-Sierra, Inc.
The Scheduler communicates directly with all of the fabric ports. Its purpose is to arbitrate the flow of cells
through the fabric from the input ports, through the fabric, to the required output ports. The Scheduler has
information about all cells that are waiting in queues at the input ports. The output ports tell the Scheduler
when they can accept new cells from the input ports. At every cell time, the Scheduler uses all of this
information to arbitrate between all of the inputs to establish the set of cells that can be transferred through
the crossbar fabric to the output queues. The effectiveness of the Scheduler at performing this arbitration
determines the throughput of the fabric under any given cell load.
The Scheduler must have accurate, up to date information in order to arbitrate efficiently and fairly.
Consequently, the EPPs send new state information to the Scheduler at every cell time.
5.1 BLOCK STRUCTURE
The block diagram of the Scheduler is shown in Figure 65 on page 255.
5.1.1 Port Block
The Scheduler can arbitrate between as many as 32 ports of OC-192c or 128 ports of OC-48c. The state
associated with each port is maintained in a port block. Each port block contains a serial link, a port control
unit, and some queue information memory. The serial link provides a full duplex, 1.6 Gbit/s,
communications channel to the appropriate EPP. This channel is used to send new request and
backpressure information to the Scheduler, and to send grant and routing tag information to the EPP.
The port control unit provides a set of registers that indicate the current status of many elements of the port
block, and that can also be used to control the behaviour of the port block. It is described further in Section
5.2 “Port State”.
The port block also has some local memory which contains the number of outstanding requests for every
queue associated with this port.
5.1.2 Arbiter Block
The arbiter receives information from each of the port blocks. This information indicates which of the virtual
output queues in each port have cells waiting to be forwarded to their appropriate destination port. At every
cell time, the arbiter combines these inputs to decide which ports can forward a cell at some fixed time in
the future. The resulting set of grants is then passed back to the port blocks.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
253
PMC [ PMC-SIERRA, INC ]
