102
Hardware Design Guide
IXP28XX Network Processor
MSF (SPI-4/CSIX/FC)
5.1.2
CSIX
CSIX-L1 (Common Switch Interface, Level 1) defines an interface between a Traffic Manager
(TM) and a Switch Fabric (SF) for ATM, IP, MPLS, and Ethernet, or similar data communication
applications.
The Network Processor Forum (NPF) controls the CSIX-L1 specification (available at
http://www.npforum.org and www.csix.org).
The unit of information transferred between Traffic Managers and Switch Fabrics is called a
CFrame, of which there are three categories:
•
Data
•
Control (for example, flow control)
•
Idle
The MSF automatically discards any Idle CFrames that it receives from the SF, and transmits Idle
CFrames to the SF when required. The MSF stores Data and Control CFrames in buffers during
transmit and receive operations. The buffers may be partitioned according to CFrame category —
guaranteeing that neither control nor data CFrames block each other.
There are two types of CSIX-L1 flow control:
•
Link Level
•
Virtual Output Queue (VOQ)
Every CFrame Base Header contains a Ready Field, which contains two Link Level flow control
bits: one for Flow Control traffic and one for Data traffic. Due to the CSIX-L1 requirement for
bounded response to Link Level flow control, the MSF manages all Link Level flow control.
Virtual Output Queue Flow Control is carried in Flow Control CFrames. As with Data CFrames,
the MSF places Flow Control CFrames in internal buffers before passing them to the Microengines
for processing.
Figure 58.
SPI-4 Clock Configuration for Dual Network Processors
1
1.
Note that when chaining clocks the jitter accumulated from the MAC, PCB, and RCLK/TCLK_REF pins must be accounted
in addition to the duty-cycle distortion.
A9317-01
IXP2800 #1
MAC
RD CLK
RCLK REF
TCLK REF
TD CLK
IXP2800 #2
RD CLK
RCLK REF
TCLK REF
TD CLK
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