CLASS OF COMPATIBLE CACHE CONSISTENCY PROTOCOLS AND THEIR SUPPORT BY THE IEEE FUTUREBUS.

Abstract

Standardization of a high-performance blackplane bus, so that it can accommodate boards developed by different vendors, implies the need for a standardized cache-consistency protocol. A class of compatible consistency protocols supported by the current IEEE Futurebus design is defined. It is referred to as the MOESI class of protocols; the term 'MOESI' is derived from the names of the states. This class of protocols has the property that any system component can select (dynamically) any action permitted by any protocol in the class, and be assured that consistency is maintained throughout the system. Included in this class are actions suitable for copyback caches, write-through caches and noncaching processors. It is shown that the Berkeley and the Dragon protocols fall within this class, and can be extended to be compatible with other members of the class. The Illinois, Firefly, and Write-Once protocols can be adapted to be compatible with this class; the facilities of the Futurebus currently do not support those protocols without adaptation.