Abstract: An arbitration logic system in a system control module regulates access to a common system bus as provided by a state machine which toggles access priority between two or more resource modules while preventing deadlock contention between two requesting modules while insuring that no module will be starved or denied access even though all the resource modules are contending for bus access. Any continuous deprivation or starvation of a module for bus access is prevented, in addition to any deadlock situations which are also prevented. This occurs by allowing retrying modules to request the bus at a temporarily higher priority and limiting the number of retries that any given requesting module is permitted to have.

Abstract: Two partitioned systems are interconnected by bus exchange modules which connect to first and second system common busses. Each system common bus shares three or more requestors, and an arbitration logic unit in each partition manages bus access priority depending on certain existing conditions. Equitable access to each system bus is allocated and no one particular requestor will be locked out from bus access. Deadlock and starvation are prevented by setting one requestor module for normal top priority but also allocating secondary priority to the remaining two requestor modules by toggling and rotating priorities among these two requestor modules. Additionally, the arbitration logic allows the two requester retrying modules to request the bus at a temporarily higher priority, but limiting the number of retry cycles allowed to any given requesting module.