Serial RapidIO (SRIO) User's Guide

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2.3.4.1 RX Operation
Mailbox1...64
fromRapidIOpacket
Header-Receivedonany
inputport
Mailboxmapper
Q15
Q2 Q1
Q0
Queueassignabletoanycore
Packetsequence
Message
n A
Packet
manager
n+1 B
n+2 B
n+3 C
n+4 D
n+5 B
n+6 E
Bufferdescriptor
queues:
Descriptorpermessage
Allpriorities
Dedicatedsingle-segment
messagedescriptorqueue
A
C
E
D
null
null
B
Multi-segmentmessage
descriptorqueue
Multi-segmentmessage
descriptorqueueN
L2memory
databuffer,upto256B
ndatapacket
n+3datapacket
n+4datapacket
n+6datapacket
256Bfreebuffer
L2memory
databuffer,upto4K
n+5datapacket
n+2datapacket
n+1datapacket
4KBfreebuffer
SRIO Functional Description
• Out-of-order responses are allowed.
• A RETRY response is issued to the first received segment of a multi-segment message when the RX
queue is busy servicing another request.
– Subsequent RETRY responses may have to be sent for received pipeline segments or additional
pipelined messages to the same queue.
• In-order message reception for dedicated flows is mode programmable.
• A queue is needed for each supported simultaneous multi-segment RX message.
• A minimum of 1.25K bytes of SRAM (64 buffer descriptors) is supported.
• The transmit source must be able to retry any given segment of a message.
• DestID is equal to port for TX operations, and the same DestID is not accessible from multiple ports.
As message packets are received by the RapidIO ports, the data is written into memory while maintaining
accurate state information that is needed for future processing. For instance, if a message spans multiple
packets, information is saved that allows re-assembly of those packets by the CPU. The CPPI module
provides a scheme for tracking single and multi-packet messages, linking messages in queues, and
generating interrupts. Figure 16 illustrates the scheme.
Figure 16. CPPI RX Scheme for RapidIO
Messages addressed to any of the 64 mailbox locations can be received on any of the RapidIO ports
simultaneously. Packets are handled sequentially in order of receipt. The function of the mailbox mapper
block is to direct the inbound messages to the appropriate queue and finally to the correct core. The
queue mapping is programmable and must be configured after device reset. RapidIO originally supported
only 4 mailboxes with 4 letters/mailbox. Letters allow concurrent message traffic between sender and
receiver. However, for messages that consist of only single packets, the unused 4-bit packet field normally
indicating the message segment extends the available number of mailboxes. Figure 17 shows the packet
header fields for message requests.
44 Serial RapidIO (SRIO) SPRUE13A – September 2006
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