Browse Prior Art Database

Version Selection Counter Comparator

IP.com Disclosure Number: IPCOM000120579D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Waldecker, D: AUTHOR

Abstract

One approach to superscalar processor design requires processor results to be placed into buffer registers prior to being placed into the architected General-Purpose Registers (GPRs). These buffers must be searched to find the most recent contents corresponding to particular GPR. The age of the buffer contents can be identified by a count. However, the count must be finite so will loop from the maximum value to the minimum. Under some circumstances, a lesser count may represent a buffer with more recent contents than a larger count. This article shows how to design a comparator which will indicate the most recent count even when the count loops from maximum to minimum value. A design with N Buffers requires k bits to represent the count of N where N<=2**k.

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Version Selection Counter Comparator

      One approach to superscalar processor design requires
processor results to be placed into buffer registers prior to being
placed into the architected General-Purpose Registers (GPRs).  These
buffers must be searched to find the most recent contents
corresponding to particular GPR. The age of the buffer contents can
be identified by a count. However, the count must be finite so will
loop from the maximum value to the minimum.  Under some
circumstances, a lesser count may represent a buffer with more recent
contents than a larger count.  This article shows how to design a
comparator which will indicate the most recent count even when the
count loops from maximum to minimum value.  A design with N Buffers
requires k bits to represent the count of N where N<=2**k.  This
disclosure shows a design which will indicate the latest count value
as long as the count contains k+1 bits.

      The concept can be illustrated by an example which has four
buffers (four possible count values).  The first column represents
all possible sequential count values and the next three columns show
the count values which should be recognized as less than the count in
the first column.  An example logic design to implement the function
is also shown.