Circuit for preventing lock-out of high priority requests to a system controller

摘要

Lock-out of pending higher high priority requests to a system controller is prevented by a circuit which comprises a counter element for counting the number of times the pending higher high priority request is not granted access. The counting results in a count value which is temporarily stored in the counter element. A compare element compares the count value to a predetermined value, the predetermined value being a predetermined number of times the data processing system will permit bypassing the pending higher high priority request. A control signal is outputted from the compare element when the count value is equal to the predetermined value and is coupled to each port to inhibit any further request for access from the equipment from being accepted by the system controller. The circuit also includes a latch element for maintaining the control signal when it is determined that a subsequent high priority request which is granted access is not the highest high priority request, the control signal being maintained until all pending high priority requests have been granted access.