Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
1.6.2.1 Subport Mode Label and MUX Fields
Label fields are arranged such that port addresses can be subdivided into four multiplexed, subport
addresses. Each segment type with a subport field utilizes bits [1:0] for the subport addresses. When
subports are not utilized, these bits will be set to zero.
Subport multiplexing shares a common physical connection to carry segments to/from each subported
linecard to a switch port. The time multiplexing between subports may be done on a quad linecard, or may
be done at an intermediate stage. When time-multiplexed, segment transmissions are sequenced between
each of the four subports through the use of a MUX field.
When a port of an LCS device uses the time-multiplexed subport mode, two bits in the Request Label_1
field of ingress and Grant Label_1 field of egress segments are used to multiplex/demultiplex each of four
subport channels. The 2-bit field is called the MUX[1:0] field. For ingress segments, the MUX[1:0] bits are
carried in the Request Label_1 field; for egress segments, the MUX[1:0] bits are carried in the Grant
Label_1 (but not the Payload Label_2). Note that for ingress traffic, this field is used to designate the
source subport of the ingress segment and is independent of the Request Label_1 subport field. Likewise
for egress traffic, the MUX field is used to designate the destination subport of the egress segment and is
independent of the Grant Label_1 and Payload Label_2 subport fields.
Segments entering the switch core must have the MUX[1:0] field correctly set. The MUX[1:0] field in
arriving segments must follow the sequence 00,01,10,11,00,... in consecutive segments. The MUX[1:0]
field in departing segments must also follow the sequence 00,01,10,11,00,... in consecutive segments.
When the MUX subport sequence must be interrupted by the need to send an Idle frame, the sequence
should continue with the next subport in sequence following the previously sent subport. The MUX[1:0]
field is placed at the beginning of the Request Label_1 or Grant Label_1 field in all segments (i.e. both data
traffic and control packets).
Segments departing or arriving at the subported line card may have the MUX[1:0] field set to correspond to
the linecard’s designated subport. Optionally, the linecard may set the MUX[1:0] field to zero, relying on an
intermediary multiplexer device to correctly set the MUX[1:0] field. In such a configuration, the LCS
prepend CRC is generated and checked masking the MUX[1:0] field to zero, enabling the intermediary
multiplexer device to independently set the MUX[1:0] field without termination and regeneration of the CRC
field. Note that without the requirement of setting the MUX[1:0] field, the linecard’s framing function does
not have to be subport aware in a system with an intermediary, time-multiplexed data stream.
1.6.3 Control Packets
The LCS link is controlled by Control Packets (CPs) that are generated by the linecard or the switch core.
When the switch core sends a CP to the linecard, it marks the correct Payload Label_2 and Type_2 fields
as a Control Packet and sends the control information in the payload data. When the linecard wishes to
send a CP to the switch core, it goes through the normal three phase request/grant/transmit process.
Control Packets have a higher priority over other traffic; therefore, grants will be returned in response to
CP request prior to other outstanding requests.
There are three categories of CPs: (1) LCS Control Packets that are used to perform low-level functions
such as link-synchronization, (2) CPU Control Packets which are used for communication between the
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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PMC [ PMC-SIERRA, INC ]
