Browse Prior Art Database

Address Compare Initiated Fetch Bypass on Memory Card

IP.com Disclosure Number: IPCOM000111072D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Blackmon, LL: AUTHOR [+5]

Abstract

A method of returning data, from a main store card that implements Fetch before Store, before the store completes is described. An address compare initiated Fetch Bypass function takes data from a store data buffer and returns it as fetch data.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 85% of the total text.

Address Compare Initiated Fetch Bypass on Memory Card

      A method of returning data, from a main store card that
implements Fetch before Store, before the store completes is
described.  An address compare initiated Fetch Bypass function takes
data from a store data buffer and returns it as fetch data.

      A main store card implementing fetch before store requires that
a store completes before the card returns fetch data for the same
address.  This means that the fetch command has to be held off until
the store completes.  Data could be returned quicker if the Fetch
data could be returned before the Store completes.  This is possible
by implementing Address Compare Initiated Fetch Bypass function.

      Compare the incoming Fetch Address with Store addresses in the
Store address buffer.  If there is a match, allow the fetch to
continue and return data from the Store Buffer rather than fetching
from Main Store.

      Referring to the Figure, the New Fetch Address-1 and Store
Addresses from the Store Address Buffer-2 are Compared-3.  If an
address compares, then the Control-4 logic initiates a bypass.  The
Fetch address needs to meet the following criteria to compare.

o   Starting Byte of Store <= Starting Byte of Fetch <= Ending Byte
    of Store

o   Ending Byte of Fetch <= Ending Byte of Store

Data is taken from the comparing entry in the Store Data Buffer-5 and
is then loaded into the Main Store Data Output Register-6, ready to
be retur...