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Browse Prior Art Database

High Performance Icache Interface for Superscalar Microprocessors

IP.com Disclosure Number: IPCOM000115057D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Miller, GD: AUTHOR [+2]

Abstract

An Icache interface which supplies up to four instructions in a single cycle to a superscalar microprocessor is described.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 67% of the total text.

High Performance Icache Interface for Superscalar Microprocessors

      An Icache interface which supplies up to four instructions in a
single cycle to a superscalar microprocessor is described.

      The Cache in the Figure is 2K bytes organized as 128 x 4 words.
Each of the 128 entries will hereafter be called a subline.

      The directory in the Figure has 32 entries.  Each entry
contains an address for compares and also a valid flag for each of
four sublines in the cache.  Each entry pointed to by the directory
will hereafter be called a line.  Each line contains four sublines.
Each subline contains words.

      There is no request from the instruction dispatcher to the
Icache controller for more instructions.  The Icache controller
assumes
that the instruction dispatcher requires four instructions each cycle
and, therefore, attempts to supply four instructions each cycle.

      There are no state machines in this design since data must be
returned each cycle.  The logic executed is all combinatorial and
must be ready for the instruction dispatcher at the start of the
following cycle.

      At the start of each cycle, two directory entries are accessed
so that in the case where the lower bits of the address are pointing
to a location in memory that is not quadword aligned, a portion of
the subsequent line will be used.  The second address into the
directory is generated by a fast incrementer.

      The Icache controller then inte...