Browse Prior Art Database

Dynamic Switch to Data Slow Mode on a Memory Card

IP.com Disclosure Number: IPCOM000111126D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Blackmon, LL: AUTHOR [+4]

Abstract

A method to dynamically switch a memory card from ECC bypass to ECC correct mode based on statistics is disclosed. The switch is synchronized between multiple cards and the cards remain in ECC correct mode until the problem is fixed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 61% of the total text.

Dynamic Switch to Data Slow Mode on a Memory Card

      A method to dynamically switch a memory card from ECC bypass to
ECC correct mode based on statistics is disclosed.  The switch is
synchronized between multiple cards and the cards remain in ECC
correct mode until the problem is fixed.

      A memory card may operate in one of two modes:  ECC bypass
(fast mode) or ECC correct (slow mode).  When operating in ECC bypass
mode, uncorrected fetch data from DRAMs is loaded into the main store
data output register.  If any data error is discovered(including a
single bit error), data is marked bad on the main store bus and the
fetch has to be retried.  If errors occur in a small section of
memory that is regularly accessed, the retries will cause the system
to slow down.  In ECC correct mode, data is corrected before it is
loaded into the main store data output register.  This means single
bit or double bit errors will not cause fetch retries since the data
will have been corrected.

      Scrubbing is a reliability feature which is used to correct
errors before they become uncorrectable.  Scrub rates are typically
chosen such that a complete card is scrubbed once per hour.  The ECC
bypass error problem is further exacerbated because it may take up to
an hour to 'scrub' a regularly accessed section of memory.

      This invention dynamically switches the memory card operation
from ECC bypass to ECC correct when triggered by runtime statistics.
This wi...