US 5,297,270 AGranted

Programmable cache memory which associates each section of main memory to be cached with a status bit which enables/disables the caching accessibility of the particular section, and with the capability of functioning with memory areas of varying size

AssigneeZenith Data Systems Corporation

InventorAnthony M. Olson

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Abstract

A system includes a main memory having a plurality of sections which each include a plurality of selectively addressable storage locations, a cache memory, and an accessing arrangement for successively requesting data from respective locations in the main memory. A method and apparatus for controlling the system involve assigning each section of the main memory a changeable status condition which is one of a caching enabled status and a caching disabled status, and inhibiting reading and storing of data by the cache memory when data requested by the accessing unit is in one of the sections of the main memory having the caching disabled status. An alternative method and apparatus for controlling the system involve selective operation in a mode in which data in the cache memory is updated even when reading of data from the cache memory is inhibited.

Claims15

Dependent claims

An apparatus comprising:

a main memory having a plurality of sections which each include a plurality of selectively addressable storage locations;
selectively settable status means for specifying for each said section of said main memory a status which is one of a caching enabled status and a caching disabled status;
accessing means for successively requesting data from respective said storage locations in said main memory;
a cache memory;
and cache control means responsive to said selectively settable status means for inhibiting reading and storing of data by said cache memory when the requested data is in one of said sections of said main memory having said caching disabled status;
wherein said cache control means is responsive to a request by said accessing means for data in a location of said main memory for storing in said cache memory a duplicate of the requested data from said main memory when said cache memory lacks a duplicate of the requested data and the requested data is in one of said sections of said main memory having si caching enabled status and for supplying the requested data to said accessing means when the requested data has previously been stored in said cache memory and is in one of said sections of said main memory having said caching enabled status;
wherein said selectively settable status means includes a register having a number of bits equal to the number of sections of said main memory and includes means responsive to said accessing means for causing said register to be loaded with data supplied by said accessing means, each said bit of said register corresponding to a respective one of said sections of said main memory and being respectively in a first logical state and a second logical state to indicate that such section has said caching enabled status and caching disabled status, respectively;
and wherein said selectively settable status means includes decoder circuit means responsive to said register and to an address from said accessing means for producing an output signal which is activated and deactivated when an address from said accessing means is within one of said sections of said memory designated by said status means as having said caching enabled status and caching disabled status, respectively, said output signal from said decoder circuit being supplied to said cache control means.

5 more elements

An apparatus comprising:

a main memory having a plurality of selectively addressable storage locations;
accessing means for successively requesting data from respective said storage locations in said main memory;
a cache memory;
and cache control means for operating said cache memory in a selected one of a first mode and a second mode, wherein in said first mode said cache control means is responsive to a request by said accessing means for data in a location of said main memory for storing in said cache memory a duplicate of the requested data from said main memory when said cache memory lacks a duplicate of the requested data and for supplying from said cache memory to said accessing means a duplicate of the requested data when said cache memory contains a duplicate of the requested data, and wherein in said second mode said cache control means is responsive to a request by said accessing means for data in a location of said main memory for storing in said cache memory a duplicate of the requested data from said main memory when said cache memory lacks a duplicate of the requested data and for preventing said cache memory from supplying data to said accessing means when said cache memory contains a duplicate of the requested data.

1 more element

An apparatus comprising:

a main memory having a plurality of sections which each include a plurality of selectively addressable storage locations;
selectively settable status means for specifying for each said section of said main memory a status which is one of a caching enabled status and a caching disabled status;
external input means for selectively specifying one of a caching enabled status and a caching disabled status;
accessing means for successively requesting data from respective said storage locations in said main memory;
a cache memory;
and cache control means for inhibiting reading and storing of data by said cache memory when the requested data is in one of said sections of said main memory for which said selectively settable status means is specifying said caching disabled status, for inhibiting reading and storing of data by said cache memory when said external input means is specifying said caching disabled status, for responding to a request by said accessing means for data in a location of said main memory when said cache memory lacks a duplicate of the requested data by storing in said cache memory a duplicate of the requested data from said main memory when said external input means is specifying caching enabled status for the location and by storing in said cache memory a duplicate of the requested data from said main memory when said selectively settable status means is specifying caching enabled status for the location and said external input means is not specifying caching disabled status, for responding to a request by said accessing means for data in a location of said main memory which has previously been stored in said cache memory by supplying the requested data to said accessing means when said external input means is specifying caching enabled status for the location, and by supplying the requested data to said accessing means when said selectively settable status means is specifying caching enabled status and said external input means is not specifying caching disabled status.

3 more elements

Dependencies are inferred from the claim text.