MSC8144E Reference Manual, Rev. 3
16-68
Freescale
Semiconductor
Serial RapidIO
®
Controller
16.3.2.8 Outbound Message Controller Arbitration
There are two ways to define the order in which each message controller sends messages from its
message queues when both outbound message controllers are enabled:
Fixed priority. The lowest numbered message unit has the highest priority. Message unit 0
has the highest priority.
Rotating priority. The message units take turns sending messages in round-robin (message
units 0, 1, 0, 1 and so on). A message controller can send 1–64 messages.
OMxMR[SCNTL] (see page 16-167) configures the message units for the fixed or rotating
modes of arbitration.
In fixed-priority arbitration, all message segments for message unit 0 must complete before
message unit 1 can start. However, in rotating priority arbitration, the other message unit can start
processing a message as soon as all message segments are transmitted. Also, in fixed-priority
arbitration when a message unit other than message unit 0 is processing a message, message unit
0 can start processing a message as soon as all message segments are transmitted.
16.3.3
Inbound Message Controller Operation
The inbound message controller receives messages and places them in a circular frame queue in
local memory. It can receive segments of a message in any order. The address to which a
message is to be written is computed as: Base a (msgseg
×
ssize in double-words). In
contrast to the outbound message controller for which software controls the enqueue pointer and
hardware controls the dequeue pointer, the inbound message controller controls the enqueue
pointer and the software controls the dequeue pointer.
Figure 16-11 depicts a sample structure of the inbound message frames and the frame pointers.
In this example, the frame queue has eight entries, three of which are currently valid. The
inbound controller controls the enqueue pointer and the software controls the dequeue pointer.
After a configured number of messages is received, an interrupt is generated to the processor.
After processing a received message, the local processor can either write the inbound message
mode register mailbox increment bit (IMxMR[MI]]), causing the dequeue pointer to point to the
next message frame in the queue, or wait until all received messages are processed and write to
the dequeue pointer.
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