Set associative sector cache

• US 4,493,026 A
• Filed: 05/26/1982
• Issued: 01/08/1985
• Est. Priority Date: 05/26/1982
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Olnowich, Howard T.
• Primary Examiner(s): Shaw, Gareth D.
• Assistant Examiner(s): Lee, Jameson
• Application Number:
  US06/382,040
• Time in Patent Office: 958 Days
• Field of Search: 364/200, 364/900
• US Class Current: 711/128
• CPC Class Codes: G06F 12/0864 using pseudo-associative means, e.g. set-associative or hashing

Abstract

A cache memory for a data processing system having a tag array in which each tag word represents a predetermined plurality or block group of consecutively addressable data block locations in a data array. The lower order set address bits concurrently access the tag word and its associated group of block locations in the data array while individual blocks within the group are accessed by supplemental block bits. Each tag word read out must compare equal with the high order bits of the address and an accompanying validity bit for each block location in its group must be set in order to effect a hit. Also described are circuits for writing into the cache and adapting the cache to a multi-cache arrangement.

Claims

1. In a data processing system including a main memory divided into sectors, each sector of the main memory including a plurality of data blocks, each data block including a plurality of data word locations, a cache memory and control means for temporarily storing selected ones of said plurality of data blocks, and a processor means connected to said main memory and to said cache memory and control means for processing data, for issuing memory addresses, and for fetching blocks of data from the cache memory or from said main memory in accordance with the issued memory addresses, said cache memory and control means comprising:

an initialization control for developing an output signal representing initialization control signals;

data array means for temporarily storing the selected ones of said plurality of data blocks;

tag array means for storing a plurality of address information therein indicative of the addresses in said main memory of the selected data blocks temporarily stored in said data array means, said address information including sector address data representative of a desired sector of said main memory wherein the data is stored, block address data representative of a desired data block of the desired sector wherein the data is stored, and validity bit data representative of the existance of the data in a desired word location of the desired data block; and

validity bit revision means connected to an output from said initialization control, connected to an output from said tag array means representative of said validity bit data of said address information stored therein, and responsive to a portion of the memory address issued by said processor means for revising and changing one or more of the validity bits of said validity bit data stored in said tag array means during an initialization period in response to said output signal from said initialization control and in accordance with said portion of the memory address issued by said processor means.

2. The cache memory and control means of claim 1, further comprising:

address select means responsive to another portion of the memory address issued by said processor means, representative of said desired data block of the desired sector wherein the data is stored, for selecting one of said plurality of address information stored in said tag array means, the selected one of said plurality of address information including a selected sector address data and a selected validity bit data.

3. The cache memory and control means of claim 2, further comprising:

sector compare means responsive to a further portion of the memory address issued by said processor means, representative of an address indicating the desired sector in the cache or the main memory wherein the data is stored, and responsive to said selected sector address data selected by said address select means for developing an output signal when said further portion of the memory address issued by said processor means and said selected sector address data selected by said address select means represent the same address.

4. The cache memory and control means of claim 3, further comprising:

validity select means responsive to the selected validity bit data selected by said address select means and to said portion of the memory address issued by said processor means for selecting a validity bit of said selected validity bit data in accordance with said portion of the memory address issued by said processor means, for developing a first output signal of one polarity when the selected validity bit has one binary state and for developing a second output signal of a polarity opposite to said one polarity when the selected validity bit has a binary state opposite to said one binary state.

5. The cache memory and control means of claim 4, further comprising:

gate means responsive to said output signal from said validity select means and to said output signal from said sector compare means for developing a hit signal in response to the existance of said output signal from said sector compare means and to said first output signal from said validity select means and for developing a miss signal in response to the existance of said output signal from said sector compare means and to said second output signal from said validity select means, said gate means developing said miss signal in response to the absence of said output signal from said sector compare means.

6. The cache memory and control means of claim 1 or 5, further comprising:

word select means connected to said data array means, responsive to one of the selected data blocks temporarily stored in said data array means, and responsive to a fourth portion of the memory address issued by said processor means for selecting a word from a word location associated with said one of the selected data blocks in accordance with said fourth portion of the memory address, for storing said word therein, and for developing an output signal indicative of the stored word; and

byte select means responsive to the output signal from said word select means and to a fifth portion of the memory address issued by said processor means for selecting a byte of said word stored in said word select means in accordance with said fifth portion of the memory address issued by said processor means, for storing said byte therein, and for developing an output signal indicative of the stored byte of said word.

7. The cache memory and control means of claim 6, further comprising:

further gate means responsive to said output signal from said byte select means and responsive to said hit signal and said miss signal for developing an output signal in response to said hit signal, said output signal being representative of a series of bytes of the word stored in said word select means, said word being associated with the blocks of data fetched from said data array means of said cache memory by said processor means,

said further gate means not developing said output signal in response to said miss signal.