METHOD FOR SEMAPHORE COMMUNICATION BETWEEN INCOMPATIBLE BUS LOCKING ARCHITECTURES

A semaphore method establishes exclusive access transactions between source and destination nodes in a multiple bus computer system, independent of the bus locking architectures of the component buses. An atomic transaction is selected for each bus protocol to mediate exclusive access transactions involving the corresponding bus, and bridges coupling different pairs of buses monitor these buses for the selected atomic transactions. A source node on one bus (the source bus) initiates an exclusive access transaction to a destination node by launching the selected atomic transaction appropriate for the source bus to the destination node. When the path between the source and the destination nodes requires transit of more than one bus, each bridge that couples a pair of buses in the path detects an incoming atomic transaction on one of these buses and launches an outgoing atomic transactions appropriate for the other bus to the destination node. In this way, the atomic transaction initiated by the source node to establish an exclusive transaction with the destination node is coupled through the buses of the system by a series of selected atomic transactions. Since each bus supports at least one atomic transaction, the semaphore method operates effectively, independent of the bus locking architectures of the buses.