RapidIO: The Next Generation Communication Fabric For Embedded Application

2.4. PACKET FORMAT

The RapidIO packet is comprised of fields from the three-level specification hierarchy. Figure 2.3 shows typical request and response packets. These examples assume the use of the parallel physical layer, packets sent over the serial physical layer are slightly different. Certain fields are context dependent and may not appear in all packets.

The request packet begins with physical layer fields. The S bit indicates whether this is a packet or control symbol. The AckID indicates which packet the fabric device should acknowledge with a control symbol. The PRIO field indicates the packet priority used for flow control. The TT, Target Address, and Source Address fields indicate the type of transport address mechanism used, the device address where the packet should be delivered, and where the packet originated. The Ftype and Transaction indicate the transaction that is being requested. The Size is an encoded transaction size. RapidIO transaction data payloads range from 1 to 256 bytes in size. The srcTID indicates the transaction ID. RapidIO devices may have up to 256 outstanding transactions between two end points. For memory mapped transactions the Device Offset Address follows. For write transactions a Data Payload completes the transaction. All packets end with a 16-bit CRC.

Figure 2.3. The RapidIO packet contains fields from the specification hierarchy

Response ...