Texas Instruments TMS320TCI648x User Manual

Page 49

www.ti.com

Switch

Endpoint

Open

Full

Open

Full

Retry

Action

Retry

Scenario A - Default

Scenario B - In order mode

Data flow destined for the

same RX queue

RX queue status when

packet arrives

RX queue status when

packet arrives

Records SourceID/letter of

first retry packet

SRIO Functional Description

Although the switch fabric delivers the segments of multi-packet messages in the order they were sent,
buffer resources at the receiving endpoint may only become available after the initial segment(s) of a
message have had to be retried. The peripheral can accept out-of-order segments and track completion of
the overall message. Scenario A in

Figure 20

shows this concept.

For applications that are set up for specific message flows between a single source and destination, it may
require in-order delivery of messages. This is described in scenario B of

Figure 20

. This scenario is similar

to scenario A, although one message may be retried due to a lack of receiver resources, subsequent
pipelined messages may arrive just as resources are freed up. This is a problem for systems requiring
in-order message delivery. In this case, the peripheral needs to record the Src_id/mailbox/letter of the first
retried message and retry all subsequent new requests until resources are available and a segment for
that Src_id/mailbox/letter is received. As long as all messages are from the same source and that source
sends (and retries) packets in order, then all messages will be received in order. Note that this solution is
less effective when multiple sources share an RX queue. The RX CPPI Control register (Address offset
0744h) sets this mode of operation on all receive queues. Once this mode is set and a retry is issued, the
queue will continue to wait for an incoming message that matches the Src_id/mailbox/letter combination. If
no such packet arrives, the RX queue is unusable in a locked state. To reenable the queue, the in-order
bit in the RX CPPI Control register must be disabled by software for that queue, after which it may be
enabled again if desired. The in-order mode of operation is only valid on multi-segment queues because
single-segment messages will never generate RETRY responses.

Figure 20. RX CPPI Mode Explanation

SPRUE13A – September 2006

Serial RapidIO (SRIO)

Submit Documentation Feedback