Northern Telecom Limited

Brian N Baker

Terry E Newell

The invention provides a mechanism for allowing a share memory/parallel processing architecture to be used in place of a conventional uni-processing architecture without requiring code originally written for the conventional system to be rewritten. Exclusive Access and Shared Read Access implementations are provided. A rollback mechanism is provided which allows all the effects of a task to be undone.

Shared memory control algorithm for mutual exclusion and rollback

A method and circuit utilizing first and second tag bits for granting access to a block of memory in a multiprocessor system having a shared memory are provided. When a memory request for exclusive access to a block of memory is granted, the starting address for that block of memory is placed in a register bank, thereby opening a semaphore. The starting address of a memory block of a subsequent memory access request is compared with the starting addresses corresponding to open semaphores within the register bank and access is denied to the requested block of memory if a match is found. The starting address associated with a request which is denied access is placed in a temporary buffer and the request is later granted access after the corresponding open semaphore becomes closed. A request which is granted memory access to a memory block which results in an open semaphore, has exclusive access to that block of memory until the semaphore is closed.

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Kanata, Canada

Brian N Baker