Abstract: Requests to memory issued by an agent on a bus are satisfied while maintaining cache consistency. The requesting agent may issue a request to another agent, or the memory unit, by placing the request on the bus. Each agent on the bus snoops the bus to determine whether the issued request can be satisfied by accessing its cache. An agent which can satisfy the request using its cache, i.e., the snooping agent, issues a signal to the requesting agent indicating so. The snooping agent places the cache line which corresponds to the request onto the bus, which is retrieved by the requesting agent. In the event of a read request, the memory unit also retrieves the cache line data from the bus and stores the cache line in main memory. In the event of a write request, the requesting agent transfers write data over the bus along with the request. This write data is retrieved by both the memory unit, which temporarily stores the data, and the snooping agent.

Abstract: A self-snooping mechanism for enabling a processor being coupled to dedicated cache memory and a processor-system bus to snoop its own request issued on the processor-system bus. The processor-system bus enables communication between the processor and other bus agents such as a memory subsystem, I/O subsystem and/or other processors. The self-snooping mechanism is commenced upon determination that the request is based on a boundary condition so that initial internal cache lookup is bypassed to improve system efficiency.

Abstract: A computer system is disclosed having a requesting bus agent that issues a communication transaction over a bus and an addressed bus agent that defers the communication transaction to avoid high bus latency. The addressed bus agent later issues a deferred reply transaction over the bus to complete the communication transaction. Special snoop ownership and cache state transition rules maintain cache coherency and processor consistency during deferred communication transactions.

Abstract: A computer system, and a method performed by it, having a mechanism for ensuring consistency of data among various level(s) of caching in a multi-level hierarchical memory system. The cache consistency mechanism includes an external bus request queue which and associated mechanism, which cooperate to monitor and control the issuance of data requests, such as read requests and write requests, onto an external bus. The computer system includes one or more CPUs each having this consistency mechanism.

Abstract: Requests to memory issued by an agent on a bus are satisfied while maintaining cache consistency. The requesting agent may issue a request to another agent, or the memory unit, by placing the request on the bus. Each agent on the bus snoops the bus to determine whether the issued request can be satisfied by accessing its cache. An agent which can satisfy the request using its cache, i.e., the snooping agent, issues a signal to the requesting agent indicating so. The snooping agent places the cache line which corresponds to the request onto the bus, which is retrieved by the requesting agent. In the event of a read request, the memory unit also retrieves the cache line data from the bus and stores the cache line in main memory. In the event of a write request, the requesting agent transfers write data over the bus along with the request. This write data is retrieved by both the memory unit, which temporarily stores the data, and the snooping agent.

Abstract: In accordance with the preferred embodiment of the present invention, a bus interface unit of a microprocessor is provided with a Micro Request Sequencer (EBMRS) disposed between a bus scheduling queue (EBBQ) and external bus control logic (EBCTL). Under normal bus request traffic, the EBMRS is effectively transparent and allows normal communication between the EBCTL and the EBBQ. However, for misaligned bus transactions, which comprise memory accesses that cross a bus width boundary, the EBMRS intercepts such transactions for special sequencing, while blocking any further requests from the EBBQ. The EBMRS separates each misaligned bus transaction request into at least first and second split transaction requests, with each split request forming a memory access that does not cross a data bus width boundary of the external bus. It then issues the first split request to the EBCTL for processing on the external bus.