RapidIO: The Next Generation Communication Fabric For Embedded Application

6.1. SYSTEM TOPOLOGY

By virtue of the use of device IDs as the system level addressing scheme, RapidIO can support virtually any system topology. The device IDs do not convey any intrinsic information about where they are located. It is the responsibility of the interconnection fabric to discover where the devices are located and to forward packets to them based on the target device ID only.

Similar to a switched Ethernet network, which makes no assumptions about the a priori location of any given Ethernet device, a RapidIO network learns, during the system discovery phase of system bringup where devices are located in the system. Switches are programmed to understand the direction, although not the exact location of all devices in a system. When device locations change, as might occur during a hot swap or failover situation, only the switches need to be reconfigured to understand the new system topology.

In RapidIO, devices communicate with other devices by sending packets that contain source and destination device IDs. These device IDs, 8- or 16-bit fields in the packet header, are used as keys by the switch fabric devices to forward the packet towards its final destination. In RapidIO, switch devices will typically use lookup tables to hold the associations between device IDs and proper output ports. RapidIO switches will be programmed to understand which of multiple output ports should be used to forward a packet with any given destination device ID. Owing to the relatively ...