Intel NETWORK PROCESSOR IXP2800 - Manual (Page 278)

278 Hardware Reference Manual
Intel
®
IXP2800 Network Processor
Media and Switch Fabric Interface
The FCIFIFO supplies two signals to Microengines, which can be tested using the BR_STATE
instruction:
1. FCI_Not_Empty — indicates that there is at least one CWord in the FCIFIFO. This signal
stays asserted until all CWords have been read. (Note that when FCIFIFO is empty, this signal
will not assert until a full CFrame has been received into FCIFIFO; as that CFrame is removed
by the Microengine, this signal will stay asserted until all CWords have been removed,
including any subsequently received CFrames.)
2. FCI_Full — indicates that FCIFIFO is above the upper limit defined in
HWM_Control[FCIFIFO_Int_HWM].
The Microengine that has been assigned to handle FCIFIFO must read the CFrame, 32 bits at a
time, from the FCIFIFO by using the
msf[read]
instruction to the FCIFIFO address; the length of
the read can be anywhere from 1 to 16. The FCIFIFO handler thread must examine the Base
Header to determine how long the CFrame is and perform the necessary number of reads from the
FCIFIFO to dequeue the entire CFrame. If a read is issued to FCIFIFO when it is empty, an Idle
CFrame will be read back (0x0000FFFF). Note that when FCIFIFO is receiving a CFrame, it does
not make it visible until the entire CFrame has been received without errors.
The nearly-full signal is based on the upper limit programmed into
HWM_Control[FCIFIFO_Int_HWM]. When asserted, this means that higher priority needs to
be given to draining the FCIFIFO to prevent flow control from being asserted to the Egress
IXP2800 Network Processor (by assertion of RXCFC).
8.5.2.2 Simplex CSIX
In Simplex Mode, the Flow Control signals are connected directly to the Switch Fabric; flow
control information is sent directly from the Egress IXP2800 Network Processor to the Switch
Fabric, and directly from the Switch Fabric to the Ingress IXP2800 Network Processor.
(See
Figure 99 .)
Figure 99. CSIX Flow Control Interface — FCIFIFO and FCEFIFO in Simplex Mode
A9764-01
TDAT
RXCSRB
TXCSRB
RXCDAT, RXCPAR, RXCSOF
TXCDAT, TXCPAR, TXCSOF
RXCFC
TXCFC
RDAT
Ingress
Intel
® IXP2800
Network Processor
Egress
Intel
® IXP2800
Network Processor
Switch
Fabric
msf[read]
FCI_Not_Empty
FCI_Full
FCIFIFO
FCEFIFO
MSF_Rx_Control[Duplex_Mode]
From MEs
To MEs