Rapidio Message Unit - Freescale Semiconductor MSC8144E Reference Manual

16.3 RapidIO Message Unit

The RapidIO message unit handles multicast and non-multicast single-segment messages and
non-multicast multiple-segment messages. The RapidIO controller has two inbound and two
outbound message controllers.
The message passing programming model for inter-processor and inter-device communication
enables a producer to send a message across the interconnect fabric to the message hardware of a
consumer, called a mailbox. The receiving mailbox hardware places the message into a queue
located in local memory. A message consists of one to sixteen segments. When a configured
number of messages is received, an interrupt is generated (if enabled) to the interrupt controller
for the processor to process the messages. Messages can be queued for transmission in the
producer memory, and the message hardware processes them sequentially. Messages can also be
queued in consumer memory while software processes them sequentially. Software can configure
the depths of the queues in the producer and consumer memories. A multicast function allows
single-segment messages to be sent to multiple consumers.
The message unit is compliant with the message passing logical specification in the RapidIO
Interconnect Specification, Revision 1.2. The message passing model is most commonly used in
systems in which a processing element is allowed to access only memory that is local to itself,
processing elements communicate with each other through message passing, and communication
is address independent.
Each inbound message controller has a dedicated interrupt to notify software that a configured
number of messages have been received. Similarly, each outbound message controller has a
dedicated interrupt to notify software that there are no more messages for the outbound mailbox
controller. The message controller is managed through a set of run-time registers.
16.3.1 Features
The message unit supports two outbound message controllers with the following features:
Chaining and direct modes.
Multicast up to 32 RapidIO destinations for single-segment messages.
Transmission to any mailbox for a single-segment message.
Transmission to any mailbox for a multi-segment message.
Segment size up to 256 bytes.
Up to 16 segment messages with a total payload of up to 4 KB.
One entire message with up to a 16 message segments can be transmitted before a
response is received.
One entire single-segment message to all multicast destinations (up to 32) can be
transmitted before a response is received.
Freescale Semiconductor
MSC8144E Reference Manual, Rev. 3
RapidIO Message Unit
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