MPC8540 datasheet(1034/1302 Pages) FREESCALE

1034 / 1302 page

MPC8540 PowerQUICC III Integrated Host Processor Reference Manual, Rev. 1

17-110

Freescale Semiconductor

RapidIO Interface

of one or more packets depending on the size of the message. When the entire message has been

received, an interrupt (if enabled) is generated for the processor to process the message. Messages

can be queued for transmission in the producer’s memory and the message hardware processes

them sequentially. Messages can also be queued in the consumer’s memory while software

processes them sequentially. Software controls the depth of the circular message queue in the

producer, or consumer.

The message unit also supports another form of message called a doorbell message. doorbell

messages do not have a data payload and are basically used for interrupting the processor. Like

data messages, doorbell messages can be queued in a consumer’s local memory while being

processed by the processor core. When a doorbell is received, an interrupt (if enabled) is

communicated to the processor.

The most common use of the message passing model is in systems where a processing element can

only access memory that is local to itself, and communication between processing elements is

achieved through message passing and communication is address independent.

There are two types of RapidIO messages. A data message may consist of up to 16 packets and

each packet may contain up to 256 bytes of data. A doorbell message contains a small amount of

software-defined information embedded in the packet header and never has a data payload.

Message and doorbell controllers are controlled through run-time registers described in

Section 17.3.3.1, “RapidIO Outbound Message Registers,” Section 17.3.3.2, “RapidIO Inbound

Message Registers,” and Section 17.3.3.3, “RapidIO Doorbell Registers.”

17.8.2 Message Unit Features

The message unit contains the following features:

•

One inbound data message structure (inbox)

•

One outbound data message structure (outbox)

•

Support for chaining and direct modes in the outbox

•

Support for up to 16 segments per message

•

Support for up to 256 bytes per packet, and up to 4 Kbytes of data per message

•

Support for one inbound doorbell message structure

•

Support for receiving messages into any mailbox, any letter

•

Support for transmitting messages from any mailbox

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