RapidIO: The Next Generation Communication Fabric For Embedded Application

2.7. GLOBALLY SHARED MEMORY

One of the protocol extensions offered in RapidIO is support for a globally shared distributed memory system. This means that memory may be physically located in different places in a system, yet will be properly cached amongst different processing elements.

For RapidIO, a directory-based coherency scheme is specified to support this. For this method each memory controller is responsible for tracking where the most current copy of each data element resides in the system. A directory entry is maintained for each device participating in the coherency domain. Simple coherency states of modified, shared, or local (MSL) are tracked for each element. For more information on the RapidIO globally shared memory (GSM) extensions refer to Chapter 13.