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Browse Prior Art Database

Deferred Refresh of Dynamic Random Access Memory (DRAM)

IP.com Disclosure Number: IPCOM000122070D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 53K

Publishing Venue

IBM

Related People

Albers, SH: AUTHOR [+4]

Abstract

Summary An algorithm is described that permits the initiation and completion of DRAM accesses with reduced delay or interruption for refresh, while still satisfying the refresh specifications for the DRAM.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 71% of the total text.

Deferred Refresh of Dynamic Random Access Memory (DRAM)

      Summary  An algorithm is described that permits the initiation
and completion of DRAM accesses with reduced delay or interruption
for refresh, while still satisfying the refresh specifications for
the DRAM.

      Background  To retain data in a DRAM it is required that the N
row addresses each be refreshed every K milliseconds (Rule 1).  For
some DRAMs, a second restriction requires that the refreshes be
distributed within the K milliseconds.  If the distribution is
uniform a refresh will occur every K/N milliseconds (Rule 2).  For
some DRAMs it is possible to relax Rule 2 providing Rule 1 is
satisfied. This means that refreshes are distributed, but also with
the provision that a limited number of refreshes "D" can be deferred.
The maximum interval between refreshes must then happen at least
every D*(K/N) milliseconds (Rule 3).

      Description  The refresh deferral algorithm is implemented in
logic control hardware that is external to the DRAM.  It satisfies
Rules 1 and 3, and defers refreshes of the DRAM in favor of accesses.
The deferral of refreshes allows a moderately accessed DRAM to reduce
its average access latency, because an anticipated refresh can be
deferred for an access.

      A counter is initialized to the maximum deferral value "D".
Each time a refresh is deferred, the counter value is decremented by
1.  If an access request can be completed before the refresh deferral...