Speed efficient cache output selector circuitry based on tag compare and data organization
First Claim
1. A cache output selector for a multi-way set-associative cache memory, said cache memory for storing a plurality of lines of data, each line data containing a plurality of words of data, and for providing for simultaneous access of words grouped as a multiple-word, said cache memory comprising a plurality of data arrays wherein consecutive multiple-words of each line of data in the plurality of lines of data reside in different data arrays in the plurality of data arrays, said cache memory comprising a switchably selectable output path for outputting an addressed multiple-word either via a pre-fetch buffer path from a set of pre-fetch latches or via a bypass path which bypasses said set of pre-fetch latches said cache output selector comprising:
- for each data array of the plurality of data arrays, a tag matching circuit for checking whether an addressed multiple-word resides in the data array and for producing a tag match signal to indicate whether the addressed multiple-word resides in the data array;
a qualifying tag match circuit which receives the respective tag match signals from each of the tag matching circuits and produces respective qualified tag match signals for each of the tag matching signals;
for each data array of the plurality of data arrays, a qualifying multiplexor which receives the respective qualified tag match signals from the qualifying tag matching circuit as data inputs, a set selector signal which selects one of said data inputs for output, and at least one qualifying signal used to qualify when said qualifying multiplexor outputs said selected data input as a qualified data array output enable signal; and
a qualifying output path select circuit which receives said respective tag match signals from each of said tag matching circuits as data input, said at least one qualifying signal as a qualifying input, and an output path select signal as a select input, said qualifying output path select circuit selecting one of said prefetch path or said bypass path from which to output said addressed multiple-word and qualifying an output enable signal.
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Abstract
A cache output selector for a multi-way set-associative cache memory which provides for simultaneous access of multiple-word data is presented. The cache memory comprises a plurality of data arrays wherein no two consecutive multiple-word reside in the same data. The cache output selector of the present invention includes, for each data array of the plurality of data arrays, a qualifying multiplexor which receives the respective tag match signals from each of the tag matching circuits as data input and a set selector signal, as selector input, and at least one qualifying signal as qualifying input. The set selector signal indicates which data array a first set of the multi-way set-associative memory resides in during a current read/write cycle. The qualifying multiplexor combines a clock qualifying functionality and a multiplexor functionality to produce a data array output enable signal in only two levels of logic. The cache memory comprises a prefetch buffer path and a bypass path from which the cache output selector selects an addressed multi-word for output. The output path selected circuit includes a pair of qualifying NOR gates. Each qualifying NOR gate combines a clock qualifying functionality and a logical NOR functionality to produce a qualified prefetch buffer path output enable signal and a qualified bypass path output enable signal respectively.
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Citations
18 Claims
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1. A cache output selector for a multi-way set-associative cache memory, said cache memory for storing a plurality of lines of data, each line data containing a plurality of words of data, and for providing for simultaneous access of words grouped as a multiple-word, said cache memory comprising a plurality of data arrays wherein consecutive multiple-words of each line of data in the plurality of lines of data reside in different data arrays in the plurality of data arrays, said cache memory comprising a switchably selectable output path for outputting an addressed multiple-word either via a pre-fetch buffer path from a set of pre-fetch latches or via a bypass path which bypasses said set of pre-fetch latches said cache output selector comprising:
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for each data array of the plurality of data arrays, a tag matching circuit for checking whether an addressed multiple-word resides in the data array and for producing a tag match signal to indicate whether the addressed multiple-word resides in the data array; a qualifying tag match circuit which receives the respective tag match signals from each of the tag matching circuits and produces respective qualified tag match signals for each of the tag matching signals; for each data array of the plurality of data arrays, a qualifying multiplexor which receives the respective qualified tag match signals from the qualifying tag matching circuit as data inputs, a set selector signal which selects one of said data inputs for output, and at least one qualifying signal used to qualify when said qualifying multiplexor outputs said selected data input as a qualified data array output enable signal; and a qualifying output path select circuit which receives said respective tag match signals from each of said tag matching circuits as data input, said at least one qualifying signal as a qualifying input, and an output path select signal as a select input, said qualifying output path select circuit selecting one of said prefetch path or said bypass path from which to output said addressed multiple-word and qualifying an output enable signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A qualifying multiplexor circuit comprising:
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a plurality of transfer gates, each coupled to receive a data input signal and each comprising a transfer gate control means for controlling whether its respective data input signal is output as a transfer gate output; a selector means responsive to a selector signal for selecting one of said plurality of transfer gates and causing said transfer gate control means of said selected transfer gate to transfer its data input signal to its respective transfer gate to produce a selected transfer signal; a NAND gate connected to receive at least one qualifying signal and which produces a NAND gate output signal; and a NOR gate connected to receive the selected transfer signal and the NAND gate output signal, which produces the qualified multiplexor output signal. - View Dependent Claims (16)
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17. A qualifying NOR circuit, comprising:
a plurality of data inputs, a first clock signal input, a second clock signal input, and a qualifier signal input, said qualifying NOR circuit combining a clock qualifying functionality and a logical NOR functionality to produce a qualified NOR output signal. - View Dependent Claims (18)
Specification