Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
subport. The LCS Grant Manager arbiter ensures that no request counter can be starved by the others;
this is described in Section 3.1.2.3 “LCS Grant Manager Arbitration”.
The size of the request counters for TDM, multicast and unicast flows allows for request counts much
larger than the input queue sizes, in order to avoid blocking requests from the input linecards. Maximum
request counter values depend on whether the EPP is in OC-48c mode, and are shown Table 20.
Table 20. Linecard Request Count Maximum Values
OC-48 port
Max Request Count
OC-192c port
Max Request Count
Traffic Type
TDM
Multicast
255
255
255
7
1023
1023
1023
7
Unicast
Control Packets
Control packet requests have the highest priority of all traffic types, are always considered to have
sufficient queue space, and are usually granted immediately. However, when the 1-in-N Idle Counter or
1-in-N NoGrant Counter expires, the LCS Grant Manager is prohibited from sending a grant during that
celltime. To allow some margin for these cases, the control packet request counters are three (3) bits wide
instead of one (1)bit.
When a TDM Sync command arrives from the Scheduler, all TDM request counters are immediately reset
to 0. If the request counters weren’t already 0, the “Linecard Requests Flushed by TDM Sync” interrupt is
raised. If a linecard sends too many requests for some flow and overflows that request counter, then the
request counter will stick at the maximum value and the “Linecard Request Count Overflow” interrupt will
be raised.
Multicast, TDM and CP tags from LCS Request labels must be stored in FIFOs corresponding to the
request counters, since these tags must be returned to the linecards as part of LCS Grant labels. These
FIFOs are contained in the Linecard Multicast Tags memory, the Linecard TDM Tags memory, and some
auxiliary registers accessed along with CP request counters in the Linecard Request Count memory.
These FIFOs are maintained within the EPP and no customer interaction is required.
3.1.2.2 Input Queue Debit Counters
Each input queue has one debit counter which is initialized to 0 at reset, incremented when the EPP sends
an LCS Grant for that queue to a linecard, and decremented when the Scheduler sends a grant for that
queue.
Control Packet queues are always considered to have 0 debits; Control Packet requests will always be
immediately granted. So there are no debit counters for Control Packet input queues. Linecards must
make sure to not overflow the Control Packet input queues (only CPU Control Packets go to the input
queues; LCS Processed Control Packets are processed and dropped immediately).
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
157
PMC [ PMC-SIERRA, INC ]
