A data processing system comprises a data processing unit coupled to a cache unit which couples to a main store. The cache unit includes a cache store organized into a plurality of levels, each for storing a number of blocks of information in the form of data and instructions. Directories associated with the cache store contain addresses and level control information for indicating which blocks of information reside in the cache store. The cache unit further includes control apparatus and a transit block buffer comprising a number of sections each having a plurality of locations for storing read commands and transit block addresses associated therewith. A corresponding number of valid bit storage elements are included, each of which is set to a binary ONE state when a read command and the associated transit block address are loaded into a corresponding one of the buffer locations. Comparison circuits, coupled to the transit block buffer, compare the transit block address of each outstanding read command stored in the transit block buffer section with the address of each read command or write command received from the processing unit. When there is a conflict, the comparison circuits generate an output signal which conditions the control apparatus to hold or stop further processing of the command by the cache unit and the operation of the processing unit. Holding lasts until the valid bit storage element of the location storing the outstanding read command is reset to a binary ZERO indicating that execution of the read command is completed.
A block access system using a cache memory comprises a first control circuit for producing a block access request for requesting read-out of all data included in a block of a predetermined size in response to an access request from an operation unit and inputting the data read out from a main memory unit into a cache memory, and a second control circuit for reading out data from the main memory unit and sending back to the first control circuit a response signal which indicates any one of execution and cancellation of the requested block access in response to the block access request from the first control means. Memory addresses necessary for reading out all the data in one block are produced by the first control circuit when the block access request is cancelled. Alternatively, memory addresses are supplied by the second control circuit when the block access request is executed.
In a cache memory arrangement used between a control processor (21) and a main memory (22) and comprising operand and instruction cache memories (31, 32), a cache buffer circuit (40) is responsive to storage requests from the central processor to individually memorize the accompanying storage data and store address data and to produce the memorized storage data and store address data as buffer output data and buffer output address data together with a buffer store request. Responsive to the buffer store request, first and second cache control circuits (36, 37) transfer for accompanying buffer output address data to the operand and the instruction cache memories, if each of the operand and the instruction cache memories is not supplied with any readout requests. Preferably, first and second coincidence circuits (51, 52) are coupled to the cache buffer circuit and responsive to the readout requests to compare all of the memorized store address data with the accompanying readout address data and to make the first and the second cache control circuits preferentially process the buffer store request prior to each of the readout requests. The buffer circuit may comprise two pairs of buffers (41, 42; 63, 64), each pair being for memorizing each of the store address data and the storage data. An address converter (70) may be attached to the arrangement to convert a logical address represented by each address data into a physical address.
A queue buffer used for the controlled buffering and transferal of data between a cache memory of a central processor unit and a mainstore memory unit. The queue buffer of the present invention preferably includes a buffer memory for the queued storage of data and a controller for directing the nominally immediate acceptance and storage of data received direct from a cache memory and for the nominally systematic background transfer of data from the queue buffer to the mainstore memory unit. This nominal prioritization of memory transfers with respect to the queue buffer memory allows data move-in requests requiring data from the main storage unit to proceed while required move-out data is moved from a cache memory immediately to the buffer queue memory.
A data processing apparatus temporarily stores data to a cache write buffer and then stores the data in a cache storing device. The cache storage device performs a data storage operation with precedence over another operation even if a store instruction contends with a read instruction for accessing the cache storing device. A storage request low signal, sent from a cache write buffer controlling device to a cache controlling device, allows a read request to have precedence over a store instruction even when there is data stored in the cache write buffer waiting to be transferred to the cache storing device in response to the store instruction. However, when the read instruction contends with the store instruction and a state transition signal, such as an instruction cancellation signal generated from an instruction controlling device, is detected, the cache write buffer controlling device changes the output signal to a storage request high signal that causes the storage operation to have precedence over the read operation.
In a storage hierarchy, promotion of data from a backing store to a caching buffer store is restricted based upon status of the cache and activity of a last storage reference. Observed writing activity selectively inhibits data promotion. Data promotion occurs after completion of a series of storage access requests. A peripheral data storage system is described.
