Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Start/Stop Control Packets
Start/Stop Control Packets are used to toggle the flow of data traffic over the link (here, data traffic is
defined to be TDM, best-effort unicast and multicast segment payloads and associated requests and
grants. i.e. all non-Control Packet segments). Start/Stop Control Packets can be sent over an LCS link in
either direction.
If a linecard sends a Stop Control Packet to the switch core, the switch core will stop sending grants to the
linecard for ingress data traffic, and will stop sending egress data traffic to the linecard. When a Start
Control Packet is sent, grants and egress data traffic resume.
If the switch core sends a Stop Control Packet to a linecard, the linecard must stop sending new data traffic
requests into the switch core until a Start Control Packet is sent.
Note that when either end has received a Stop Control Packet, it can continue to request, grant, send and
receive all categories of Control Packets.
When an LCS link powers-up, it will be in Stop mode: i.e. it will act as if a Stop Control Packet has been
sent in both directions.
Table 14. Start/Stop Control Packet Format
Size
(bits)
Field
Definition
CP_Type
Start/Stop
Unused
8
1
00000010
1=Start, 0=Stop.
55
16
Set to zero.
CRC-16
16-bit CRC calculated over 10-byte control packet payload.
1.6.3.2 CPU Control Packets
CPU Control Packets are specified by setting the Label_1/Label_2 Field to 14’h0001 (CP-category for
CPU Control Packets) and associated Type Field to 4’h0 (Type for Control Packets).
When the linecard sends a CPU CP to the switch core CPU, the complete payload data is passed to the
switch core CPU. Likewise, when the switch core sends a CPU CP to the linecard, the complete payload
data is passed to the linecard.
No flow control mechanism is explicitly implemented for CPU CPs, and will be implementation dependent.
72
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
PMC [ PMC-SIERRA, INC ]
