Hierarchy response priority adjustment mechanism

Abstract

A response priority circuit arrangement for determining the priority among simultaneous responses from different access-time levels L3 and L2 in a storage hierarchy to maintain nearly the same order among the simultaneous responses as the order of their storage access requests. The storage requests were put into an indexed slot in a hardware queue. The index of the assigned queue slot is sent to a basic storage module (BSM) part of the hierarchy which is selected by the storage address supplied by the processor making the storage request. The selected BSM will have the requested data either in its main memory part (L3) or in its high-speed buffer part (L2). The priority circuit arrangement has a separate group of AND gates for each hierarchy level L3 and L2. The groups are interlocked by a circuit which disables the L2 group if any AND gate is enabled in the L3 group. Only one AND gate can be enabled in both L3 and L2 groups. When simultaneous responses are signalled from the L3 and L2 levels, the L3 gate is given priority since the L3 response resulted from an earlier request than the L2 response. The output of the enabled AND gate indicates the index of the slot in the queue which contains the request matching the response given priority. A bus connection can then be made using that slot's information for the data transfer between the selected BSM and the requesting processor.