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Browse Prior Art Database

Improved Misaligned Cache Access Using Shadow Bits

IP.com Disclosure Number: IPCOM000117991D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Downey III, WJ: AUTHOR [+2]

Abstract

Disclosed is a process for improving the misaligned performance of a cache access that crosses a line boundary. This is important since most high performance microprocessors rely on this fast access for peak performance.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 76% of the total text.

Improved Misaligned Cache Access Using Shadow Bits

      Disclosed is a process for improving the misaligned performance
of a cache access that crosses a line boundary.  This is important
since most high performance microprocessors rely on this fast access
for peak  performance.

      A cache is typically made up of several rows of multiple
words.  During an aligned access one of these multiple words is read
out of one of the many rows.  This can be accomplished in a single
access.  Many caches however can be accessed on a boundary which is
other than the normal word boundary.  For example, a cache may be
accessible on a byte boundary when the words are 32 bits long or four
bytes.  If a  word access is attempted on a byte boundary other than
the initial byte  of the word, an additional byte or bytes would have
to be read from the  next word.  This is called a misaligned access.
This is not a problem  and can be accomplished in a single access as
long as the next word is  in the same row as the word the access
started in.  The problem arises  when the misaligned access is
attempted on the last word of a row. In  this case the next word
would be in the next row.  In a standard cache  only one row can be
turned per access.  This would require an additional  access to
retrieve the rest of the word from the next row.  Please refer  to
Fig. 1 for a graphical view of this.

      The proposed solution to the above problem involves adding
addition...