82845PE Datasheet, PDF (131/176 Pages) Intel Corporation – 82845GE Graphics and Memory Controller Hub (GMCH) and 82845PE Memory Controller Hub (MCH)

Functional Description
5.4.2
5.4.2.1
5.4.2.2
5.4.2.3
Video Engine
Hardware Motion Compensation
The Motion Compensation (MC) process consists of reconstructing a new picture by predicting
(either forward, backward, or bidirectionally) the resulting pixel colors from one or more reference
pictures. The GMCH receives the video stream and implements Motion Compensation and
subsequent steps in hardware. Performing Motion Compensation in hardware reduces the
processor demand of software-based MPEG-2 decoding, and thus improves system performance.
The Motion Compensation functionality is overloaded onto the texture cache and texture filter. The
texture cache is used to typically access the data in the reconstruction of the frames and the filter is
used in the actual motion compensation process. To support this overloaded functionality the
texture cache additionally supports the following input formats:
• YUV420 planar
Sub-Picture Support
Sub-picture is used for two purposes; one is Subtitles for movie captions, etc. which are
superimposed on a main picture, and another is for Menus to provide some visual operation
environments for the user of the player.
A DVD allows movie subtitles to be recorded as Sub-pictures. On a DVD disc, it is called
“Subtitle” because it has been prepared for storing captions. Since the disc can have a maximum of
32 tracks for Subtitles, they can be used for various applications; for example, as Subtitles in
different languages or other information to be displayed.
There are two kinds of Menus, the System Menus and other In-Title Menus. First, the System
Menus are displayed and operated at startup of or during the playback of the disc or from the stop
state. Second, In-Title menus can be programmed as a combination of Sub-picture and Highlight
commands to be displayed during playback of the disc.
The GMCH supports sub-picture for DVD and DBS by mixing the two video streams via alpha
blending. Unlike color keying, alpha blending provides a softer effect and each pixel that is
displayed is a composite between the two video stream pixels. The GMCH can utilize four methods
when dealing with sub-pictures. The flexibility enables the GMCH to work with all sub-picture
formats.
Planes
A plane consists of a rectangular shaped image that has characteristics such as source, size,
position, method, and format. These planes get attached to source surfaces, which are rectangular
memory surfaces with a similar set of characteristics. They are also associated with a particular
destination pipe.
Cursor Plane
The cursor plane is one of the simplest display planes. With a few exceptions, it has a fixed size of
64x64 and a fixed Z-order (top). In legacy modes, the cursor can cause the display data below it to
be inverted.
Intel^® 82845GE/82845PE Datasheet
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