RapidIO: The Next Generation Communication Fabric For Embedded Application

11.5. MULTICASTING SYMBOLS

A special characteristic of the RapidIO parallel and serial physical layers is the ability to multicast certain control symbols. The multicast-event control symbol provides a mechanism through which notice that some system-defined event has occurred, can be selectively multicast throughout the system.

When a switch processing element receives a Multicast-Event control symbol, the switch is required to forward the multicast-event by issuing a multicast-event control symbol from each port that is designated in the port's CSR as a multicast-event output port. A switch port should never forward a multicast-event control symbol back to the device from which it received a multicast-event control symbol, regardless of whether the port is designated a multicast-event output or not.

It is intended that at any given time, a single device will source multicast-event control symbols. However, the source device can change (in case of failover, for example). In the event that two or more multicast-event control symbols are received by a switch processing element close enough in time that more than one is present in the switch at the same time, at least one of the multicast-event control symbols shall be forwarded. The others may be forwarded or discarded (device dependent).

The system-defined event whose occurrence is signaled by a multicast-event has no required temporal characteristics. It may occur randomly, periodically, or anything in between. For instance, a ...