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306 Hardware Reference Manual
Intel
®
IXP2800 Network Processor
Media and Switch Fabric Interface
The backpressure signal (TXCFC, RXCFC) is an asynchronous signal and is asserted by the
ingress network processor to prevent overflow of the ingress network processor ingress flow
control FIFO. If the egress network processor is so optionally configured, it will react to assertion
of the backpressure signal for 32 clock cycles (64 edges) as a request for a de-skew training
sequence to be transmitted on the flow control interface.
The flow control interface only supports a 32-bit CWord. Flow Control CFrames that are received
by the egress network processor are stripped of any padding associated with large CWord widths
and forwarded to the flow control interface.
The various options for parity calculation and checking supported on the data interface are
supported on the flow control interface. Horizontal parity checking may be optionally disabled.
The standard calculation of vertical parity may be replaced with a DIP-16 calculation.
8.9.4.2.3
Support for Simplex Operation
The network processor supports a mode of operation that supports the CSIX-L1 protocol, but offers
an independent interface for the ingress and egress network processors. In this mode, the ingress
and egress network processors each offer an independent full-duplex CSIX-L1 flavor of interface
to the fabric, but the network processor-to-fabric interface on the egress network processor and the
fabric-to-network processor interface of the ingress network processor are of reduced width,
consisting of four (instead of 16) data signals. These narrow interfaces are referred to as Reverse
Path Control Interfaces and use the same physical interface as the flow control interface in the
dual-chip, full duplex configuration. They support the transfer of Flow Control CFrames and the
CRdy and DRdy “ready” bits, but are not intended to support the transfer of data CFrames.
The Reverse Path Control Interfaces (RPCI) support only the 32-bit CWord width of the dual chip,
full duplex flow control interface. The variations of parity support provided by the data interface
and the flow control interface are supported by the RPCI.
Figure 114. Reference Model for IXP2800 Support of the Simplex Configuration Using
Independent Ingress and Egress Interfaces
B2752-01
Primary
Interface
RPCI
Fabric
Interface
Chip(s)
Primary
Interface
RPCI
Ingress
Network
Processor
Egress
Network
Processor
Printed Circuit Card