RapidIO: The Next Generation Communication Fabric For Embedded Application

5.2. MESSAGE TRANSACTIONS

The RapidIO Message Passing Logical Specification defines two different packet formats for use in messaging. The Type 10 packet format is used for sending very short, 16-bit data payloads. The Type 10 packet is known as the DOORBELL transaction format. DOORBELL transactions are well suited for sending interrupts between processors. The Type 11 packet is used for sending data payloads of up to 4096 bytes using multiple transactions. The Type 11 packet transaction is called the MESSAGE transaction. These transactions will now be described in more detail.

5.2.1. Type 10 Packet Format (Doorbell Class)

The Type 10 packet format is the DOORBELL transaction format. Type 10 packets never have data payloads. The field value 0b1010 specifies that the packet format is of Type 10.

The doorbell operation (Figure 5.1), consisting of the DOORBELL and RESPONSE transactions (typically a DONE response) as shown below, is used by a processing element to send a very short message to another processing element through the interconnect fabric. The DOORBELL transaction contains the info field which is used to hold the transaction information. The transaction does not have a data payload. The info field is software defined, and can be used for any desired purpose. Typically the operating system running on the processor would define the meaning of the info field used in DOORBELL transactions.

Figure 5.1. Doorbell operation

Figure 5.2. Doorbell message packet format (Type ...