Browse Prior Art Database

Self-Aligning Multidecode Mechanism

IP.com Disclosure Number: IPCOM000114855D
Original Publication Date: 1995-Feb-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Emma, PG: AUTHOR [+6]

Abstract

In a high-speed multidecoder wherein predetermined nybble locations are used to demultiplex a multiported register-file, it is possible to observe upcoming instruction combinations, and to pre-align them for a subsequent successful multidecode when their canonical alignment would have precluded such. This invention is a mechanism that performs this function.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 57% of the total text.

Self-Aligning Multidecode Mechanism

      In a high-speed multidecoder wherein predetermined nybble
locations are used to demultiplex a multiported register-file, it is
possible to observe upcoming instruction combinations, and to
pre-align them for a subsequent successful multidecode when their
canonical alignment would have precluded such.  This invention is a
mechanism that performs this function.

      The Decode and Address Generation path is a cycle-time limiting
path in any high-speed computer.  This cycle comprises the steps of
outgating instructions from an instruction-buffer, selecting register
descriptor fields from the appropriate nybbles of the instructions
(based on the instruction opcode), using those descriptors to outgate
the contents of the appropriate registers from a multiported
register-file in parallel, adding the appropriate selected register
contents to form an address, and gating this address to an address
register.

      To implement a multidecoder in a machine that supports several
instruction formats, nybble selection must be completely general,
i.e., the appropriate register descriptors for the second instruction
may be in any of several places based on the format of the first
instruction.  This generality can only be supported by adding a level
of multiplexing on the nybble selection, or by multiporting the
register-file further to accommodate more superfluous read
operations.  Either approach adds circuits to the critical pat...