Digital Equipment Corporation

W Hugh Durdan

G Michael Uhler

Robert Dickson

Rebecca L Stamm

George M Uhler

Michael A Callander

Hoe To Cho

William J Bowhill

Maw Z Jau

In a computer system, a mother-board is used to physically connect processor, memory, and input/output modules. The mother-board includes an adaptable processor bus for connecting the processor and memory modules, and an input/output bus for connecting the input/output modules, the processor and input/output bus are decoupled for communicating. A processor module including a bridge is used to coupled the processor and input/output buses, and to adapt the processor bus to a particular processor architectures.

Apparatus and method for adapting a computer system to different

Multi-processor systems are often implemented using a common system bus as the communication mechanism between CPU, memory, and I/O adapters. It is also common to include features on each CPU module, such as cache memory, that enhance the performance of the execution of instructions in the CPU. Many architectures require that the hardware employ a mechanism by which the data in the individual CPU cache memories is kept consistent with data in main memory and with data in other cache memories. One such method involves each CPU monitoring transactions on the system bus, and taking appropriate action when a transaction appears on the bus which would render data in the CPU's cache incoherent. If the CPU uses queues to hold records of incoming transaction information until it can service them, the bus interface must guarantee that the queued items are processed by the cache in the correct order. If this is not done, certain types of shared data protocols fail to operate correctly. The present invention describes a method by which hardware can guarantee the serialization of transactions requiring service by the CPU cache. The serialization method described guarantees that shared memory protocols operate correctly.

Multi-processor computer system having shared memory, private cache

An apparatus which filters the number of invalidates to be propagated onto a private processor bus is provided. This is desirable so that the processor bus is not overloaded with invalidate requests. The present invention describes a method of filtering the number of invalidates to be propagated to each processor. A memory interface filters the invalidates by using a second private bus, the invalidate bus, which communicates with the cache controller. The cache controller can tell the memory interface whether data corresponding to the address on the invalidate bus is resident in the private cache memory of that processor. In this way, the memory interface only has to request the private processor bus when necessary, in order to perform the invalidate.

Method and apparatus for filtering invalidate requests

A method for synchronizing data transfers in a data processing system is presented. The invention includes two separate clocks generated by a slave processor, one of which is used to synchronize outgoing signals from the communicating elements and the second of which is used to synchronize incoming signals to the communicating elements.

Efficient protocol for communicating between asychronous devices

A protocol for transferring instructions between asynchronous processors in a computer system is provided. Each instruction transfer requires the transfer of an opcode and a variable number of operands. The transfer is accomplished via a bus which interconnects the processors. The opcode and operands are assembled in a buffer in the sending processor and then transferred to the receiving processor in reverse order, i.e., operands first and opcode last. The receiving processor does not acknowledge any of the transfers until it receives the opcode which is always sent last. Upon receipt of the opcode, the receiving processor knows the instruction transfer is complete and sends the acknowledge signal immediately thereafter.

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Waban, MA, United States of America

W Hugh Durdan