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Hardware Reference Manual 301
Intel
®
IXP2800 Network Processor
Media and Switch Fabric Interface
8.9.3 SPI-4.2 Support
Data is transferred across the SPI-4.2 interface in variously-sized bursts and encapsulated with a
leading and trailing control word. The control words provide annotation of the data with port
address (0-255) information, start-of-packet and end-of-packet markers, and an error detection
code (DIP-4). Data must be transferred in 16-byte integer multiples, except for the final burst of a
packet.
The status interface transfers state as an array of state or calendar, two bits per port, for all of the
supported ports. The status information provides for reporting one of three status states for each
port (satisfied, hungry, and starving) corresponding to credit availability for the port. The mapping
of calendar offset to port is flexible. Individual ports may be repeated multiple times for greater
frequency of update.
8.9.3.1 SPI-4.2 Receiver
The network processor receiver stores received SPI-4.2 bursts into receiver buffers. The buffers
may be configured as 128 buffers of 64 bytes, 64 buffers of 128 bytes, or 32 buffers of 256 bytes.
Information from the control words, the length of the burst, and the TCP checksum of the data are
stored in an additional eight bytes of control storage. The buffers support storage of bursts
containing an amount of data that is less than or equal to the buffer size. A burst that is greater than
the configured size of the buffers is stored in multiple buffers. Each buffer is made available to
software as it becomes filled.
As the filling of each buffer completes, the buffer is dispatched to a thread of a Microengine that
has been registered in a free list of threads, and the eight bytes of control information are forwarded
to the register context of the thread. If no thread is currently available, the receiver waits for a new
thread to become available as other buffers are also filled (and then also have “waiting queues”).
Figure 112. SPI-4.2 Interface Reference Model with Receiver and Transmitter Labels
Corresponding to Link Layer Device Functions
B2750-01
PHY
Device
Link
Layer
Device
Receiver
Signals
SPI-4.2
Interface
Transmitter
Signals
Ingress
Intel
®
IXP2800
Network
Processor
Egress
Intel IXP2800
Network
Processor