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Conditional Least-Recently-Used Data Cache Design to Support Multimedia Applications

IP.com Disclosure Number: IPCOM000111404D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 124K

Publishing Venue

IBM

Related People

Chan, JC: AUTHOR [+5]

Abstract

The multimedia market has recently been generating considerable interest. It has been observed that by the turn of the century, most companies will be implementing PC/Workstation-based multimedia applications that provide users as indespensible tools for enhancing corporate productivity. In the past, PC owners generally rely on special hardware to run multimedia applications (e.g., display motion video). But many observers believe that "software" holds the key to a range of low cost multimedia products and services. For example, Microsoft's Video for Windows* works without special hardware on PCs powered by Intel's 386 and 486 microprocessors. Apple's Quicktime** is another example.

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Conditional Least-Recently-Used Data Cache Design to Support Multimedia
Applications

      The multimedia market has recently been generating considerable
interest.  It has been observed that by the turn of the century, most
companies will be implementing PC/Workstation-based multimedia
applications that provide users as indespensible tools for enhancing
corporate productivity.  In the past, PC owners generally rely on
special hardware to run multimedia applications (e.g., display motion
video).  But many observers believe that "software" holds the key to
a range of low cost multimedia products and services.  For example,
Microsoft's Video for Windows* works without special hardware on PCs
powered by Intel's 386 and 486 microprocessors.  Apple's Quicktime**
is another example.  The development of software-based multimedia
products will continue to attract many multimedia vendors as long as
chip manufacturers continue to deliver high speed microprocessors at
the resaonable cost.

      It has been shown that one of the performance bottlenecks in
running multimedia applications is the time spent in processing
compressed audio/vedio data (i.e., the decompression process).  Since
most of the multimedia applications are real-time (or at least time
guaranteed), any excessive delay incurred in decompressing the data
will cause severe damage to the sound and video quality.  Therefore
it is essential to design a processor that minimizes the delay in
processing multimedia data and yet retains the power in processing
other applications.

      Due to the advance of VLSI technology, most of today's high
performance processors are designed with an on-chip data cache.  One
key parameter in designing a data cache is the choice of the
replacement policy.  A most commonly implemented cache replacement
policy is called the RU LRU (Least Recently Used) algorithm.  This
algorithm is based on the use of the principle of temporal locality:
If an item is referenced, it will tend to be referenced again soon.
Therefore, if recently used cache lines are likely to be used again,
then the best candidate for disposal is the least recently used.
However, this assumption does not apply to processing compressed
audio/video data, since once data items are used to reconstruct a
short playback of sound or a segment of video image, it is unlikely
that they will be used again to reconstruct the subsequent sound or
image.

      To overcome this problem, proposed is a new variation on the
use of the LRU algorithm which supports applications in multimedia
environment.  The idea is very simple.  When a cache line is to be
selected for disposal, a line which contains multimedia data will be
considered first.  If  no such lines exist, then normal LRU selection
will be resumed.  In order to support this idea, minor hardware and
software changes are required.  We outline the changes as follows:

1.  One or more dedicated ha...