Abstract: A shared memory multiprocessor having a packet switched bus, together with write back caches for connecting individual processor to that bus, employs a consistency protocol that permits the caches to store multiple copies of read/write data at identical physical addresses for use as needed by the respective processors. The protocol causes the hardware to automatically and transparently maintain the consistency of this data. To that end, the caches detect when a datum becomes shared by monitoring the traffic on the bus, thereby enabling them to broadcast an updating write on the bus whenever their respective processors issue a write to a shared address. If desired, this protocol may be extended to include an advisory invalidate for reducing the amount of address sharing that occurs, thereby enhancing the efficiency of the protocol. The protocol maintains a consistent view of memory for the processors, while permitting I/O devices to have direct access to the memory system.

Abstract: Virtual addresses from multiple address spaces are translated to real addresses in main memory by generating for each virtual address an address space identifier (AID) identifying its address space. Then, the virtual address and its AID are used to obtain the real address. The address spaces include a shared address space, from which the processor can provide a virtual address at any time, as well as switched address spaces, from one of which the processor can provide a virtual address at a given time. If the processor's local cache does not have data for the virtual address and cannot translate the virtual address to a real address, the local cache provides the virtual address on a bus. A dedicated VLSI map cache is connected for receiving virtual addresses from the bus and for providing real addresses on the bus. The bus is also connected for providing real addresses to access memory.

Abstract: A high speed, synchronous, packet-switched inter-chip bus apparatus and method for transferring data between multiple system buses and a cache controller. In the preferred embodiment, the bus connects a cache controller client within the external cache of a processor to a plurality of bus watcher clients, each of which is coupled to a separate system bus. The bus allows the cache controller to provide independent processor-side access to the cache and allows the bus watchers to handle functions related to bus-snooping. An arbiter is employed to allow the bus to be multiplexed between the bus watchers and cache controller. Flow control mechanisms are also employed to ensure that queues receiving packets or arbitration requests over the bus never overflow. A default grantee mechanism is employed to minimize the arbitration latency due to a request for the bus when the bus is idle.

Abstract: Virtual addresses from multiple address spaces are translated to real addresses in main memory by generating for each virtual address an address space identifier (AID) identifying its address space. Then, the virtual address and its AID are used to obtain the real address. The address spaces include a shared address space, from which the processor can provide a virtual address at any time, as well as switched address spaces, from one of which the processor can provide a virtual address at a given time. A dedicated VLSI map cache translates by keeping the most recently accessed mapping entries, each of which associates a virtual address and its AID with a real address. If the virtual address is from the shared address space, the map cache uses the shared AID, but if not, the map cache uses the current switched AID for the processor providing the virtual address.