Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Enhanced Port Processor - Flow Control Crossbar
If CRC errors occur between the Flow Control Crossbar device and the EPP, the input EPP will not have
the correct view of the available space in the egress queues of the output EPP. Thus, a refresh of the
output queue credits must be performed. The invalid incremental credit interrupt register is used to indicate
which input port to output port flow has lost output queue credits. For example, if port 5’s invalid
incremental credit interrupt register has a value of 0x400, then there are lost credits for all Unicast flows
from input port 5 to output port 10. See Section 1.9.3 “Flow Control Refresh Procedure” on page 97.
Enhanced Port Processor - Scheduler
In a non-redundant Scheduler configuration, CRC errors that occur between the Enhanced Port Processor
and Scheduler might result in inconsistent state information. The Scheduler must have accurate
information on the number of outstanding requests as well as the backpressure state of all VIQs. A lost
request or grant can cause a discrepancy between the Enhanced Port Processor and Scheduler. Figure 41
describes a simple non-redundant Scheduler configuration where Enhanced Port Processor 1 and
Enhanced Port Processor 2 are connected to Scheduler 0.
If Enhanced Port Processor 1 receives a CRC error on information from Scheduler 0, then Enhanced Port
Processor 1 does not know if that information contained a valid grant. If the corrupted grant was for unicast
traffic, then the Enhanced Port Processor would have one more request than the Scheduler; this might
delay the forwarding of one cell. However, if the corrupted grant was for multicast traffic, then the next
multicast grant might cause a cell to be sent to the wrong destination port. This is considered unacceptable
and so a CRC error from Scheduler-0 makes Enhanced Port Processor 1 ignore all subsequent Scheduler
grants until the state information can be restored. As always, the CRC error is indicated to the local CPU
which must refresh Scheduler 0 before traffic can continue to flow to/from this port. The Enhanced Port
Processor continues to receive routing tags from the Scheduler, and will forward cells received from other
ports.
If Scheduler 0 receives a CRC error on information from Enhanced Port Processor- , then Scheduler 0 may
have lost a new request or backpressure information. If the lost information was a unicast request, then the
Scheduler would have one less request than the Enhanced Port Processor. This might delay the
forwarding of one cell. If the lost information was a multicast request, the Scheduler might send a cell to
the wrong destination port. If back pressure assertion was lost, the Scheduler could possibly overflow the
output queues. These behaviors are considered unacceptable. Thus, when Scheduler 0 detects a CRC
error it disables traffic to/from Enhanced Port Processor 1 until the CPU refreshes Scheduler 0’s state
information. Traffic to/from other ports continues to flow. The CRC error is indicated to the CPU which must
then refresh the state information in Scheduler 0. See Section 1.9.4 “Scheduler Refresh Procedure” on
page 98.
94
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
PMC [ PMC-SIERRA, INC ]
