Browse Prior Art Database

Memory Card Data Fastpath

IP.com Disclosure Number: IPCOM000111259D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Blackmon, LL: AUTHOR [+5]

Abstract

A method to decrease the latency in returning data from a memory card to a processor is disclosed. The data is returned using a fastpath, which bypasses the ECC logic. A flag is sent along with the data to indicate that it is good or bad.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 75% of the total text.

Memory Card Data Fastpath

      A method to decrease the latency in returning data from a
memory card to a processor is disclosed.  The data is returned using
a fastpath, which bypasses the ECC logic.  A flag is sent along with
the data to indicate that it is good or bad.

      A memory card is required to return fetch data to the processor
as fast as possible.  The biggest delay contributor in the fetch
return is the DRAM access time.  Over time, processor cycle times
have decreased by an order of magnitude.  The DRAM access times have
also decreased, but have not kept pace with the processor
improvements.  As a result, a fetch to the memory card takes several
processor cycles.  This delay may stop the processor and impact
system performance.  Reducing this latency by only a few cycles can
improve system performance by several percent.

The memory card fetch return can be broken up into three parts:

1.  Command processing

2.  DRAM access

3.  Data processing

      This invention focuses on the data processing part.  Fetch data
is returned from the memory card to the processor as soon as possible
using a data fastpath.  The fastpath bypasses the ECC logic.  A flag
(or stomp bit) is sent along with the data to indicate that it is
good/bad.

      The fastpath assumes that data is correct most of the time.
The stomp bit is used for cases where there is a data error.  It does
not indicate that the data was correctable, only that there was an
erro...