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Graphics using System Memory for Frame Buffers and no Video Random Access Memory

IP.com Disclosure Number: IPCOM000114776D
Original Publication Date: 1995-Jan-01
Included in the Prior Art Database: 2005-Mar-29
Document File: 6 page(s) / 198K

Publishing Venue

IBM

Related People

Lawless, WF: AUTHOR

Abstract

Rendering in 2D Graphics Adapters usually takes place into unique Frame Buffers, mostly Video Random Access Memory (VRAM) which is dual ported for refreshing the pixels on the screen and not relying on reading the data back out. VRAMs are very expensive to use for they typically cost twice as much as DRAM. VRAM is the most expensive part of 2D graphics adapters and makes it very hard to be competitive in the low end market segments. With the disclosed approach you can eliminate the VRAM and extra memory from the graphics design and use the already existing System Memory for the Frame Buffers. Not only is this design less expensive - you will see a marked improvement in performance over the VRAM Approach. This will offer a much better price per performance offering to our customers.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 26% of the total text.

Graphics using System Memory for Frame Buffers and no Video Random
Access Memory

      Rendering in 2D Graphics Adapters usually takes place into
unique Frame Buffers, mostly Video Random Access Memory (VRAM) which
is dual ported for refreshing the pixels on the screen and not
relying on reading the data back out.  VRAMs are very expensive to
use for they typically cost twice as much as DRAM.  VRAM is the most
expensive part of 2D graphics adapters and makes it very hard to be
competitive in the low end market segments.  With the disclosed
approach you can eliminate the VRAM and extra memory from the
graphics design and use the already existing System Memory for the
Frame Buffers.  Not only is this design less expensive - you will see
a marked improvement in performance over the VRAM Approach.  This
will
offer a much better price per performance offering to our customers.

No VRAM Approach

      This is a proposal for a memory controller design which uses
System Memory for the Frame Buffers and no VRAM (Fig. 1).  In the
last several years, 2D approaches keep getting beat up because of
COST, this approach uses the already existing System Memory and takes
away the very expensive VRAM cost.  This idea is geared for low end
systems such as PCs and Low End Workstations.

The COST savings are as follows given the following system
configurations.
  o  For 8 Bit SB, no WID/OL 1024 x 768 = 4 VRAMS.  Savings of $44.00
  o  For 8 Bit SB, 8 Bit WID/OL 1024 x 768 = 8 VRAMS.  Savings of
$88.00
  o  For 8 Bit SB, no WID/OL 1280 x 1024 = 5 VRAMS.  Savings of
$55.00
  o  For 8 Bit SB, 8 Bit WID/OL 1280 x 1024 = 10 VRAMS.  Savings of
      $110.00
  o  For 24 Bit SB, 8 Bit WID/OL 1280 x 1024 = 20 VRAMS.  Savings of
      $220.00

Some Assumptions:
  o  System Memory is Sync DRAM at used at 20 nsec cycles.
  o  Data width of System  Memory is 144 Bits or 16 Bytes + Parity.
  o  VRAM Cost of $11.00 for a 2 Megabit chip.

      For Cost reasons this approach is an obvious win but now let's
look at the performance to see that the speeds and feeds are even
better than that of a similar more expensive VRAM approach.

      Several things to look at are: does the processor's use of
the system memory bus get worse? is the rendering time going to be
better?, and does the time on the system memory bus to refresh the
monitor affect the first two?

Activity on the System Memory Bus
  o  Screen updates at a refresh rate of 77Hz.
  o  Pixel Level Rendering.
  o  System Memory code execution or moving data into L2 Cache.

Performance issues to look at with the following pixel depths:
  o  8 Bit Per Pixel Color Data
  o  24 Bit Per Pixel Color Data
  o  8 Bit Color Data with 8 Bits of WID/OL
  o  24 Bit Color Data with 8 Bits of WID/OL
  8 Bit per pixel data

Speeds to look at:
  o  Burst Rate to keep up with 77 Hz screen refresh rate.
  o  % of time on the bus to refresh monitor.
  o  % of time on the bu...