
Intel
82815EM GMCH
R
140
Datasheet
4.12.8.
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
GMCH2-M intercepts the DVD pipeline at Motion Compensation 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 GMCH2-M’s implementation of Hardware Motion Compensation supports a motion smoothing
algorithm. When the system processor is not able to process the MPEG decoding stream in a timely
manner (as can happen in software DVD implementations), the Intel
815EM chipset GMCH2-M
supports downsampled MPEG decoding. Downsampling allows for reduced spatial resolution in the
MPEG picture while maintaining a full frame rate, and thus reduces processor load while maintaining the
best video quality possible given the processor constraints.
4.12.9.
Hardware Cursor and Popup Support
The internal graphics device of the GMCH2-M allows an unlimited number of cursor patterns to be
stored in the display cache or system memory. Two sets of registers, contain the x and y position of the
cursor relative to the upper left corner of the display. The following four cursor modes are provided:
32x32 2 bpp AND/XOR 2-plane mode
64x64 2 bpp 3-color and transparency mode
64x64 2 bpp AND/XOR 2-plane mode
64x64 2 bpp 4-color mode
Intel
815EM chipset implements a popup in addition to the cursor. The Intel
815EM chipset popup
and cursor have the same functionality as the Intel
815E chipset cursor. The Intel
815EM chipset
popup is implemented by replicating the cursor logic, it is allowable for both the cursor and the popup to
be active on the screen at the same time.
4.12.10. Overlay Engine
The overlay engine provides a method of merging either video capture data (from an external PCI Video
Capture Adapter) or data delivered by the processor, with the graphics data on the screen. Supported data
formats include YUV 4:2:2, YUV 4:2:0, YUV 4:1:0, YUV 4:1:1, RGB15, and RGB16. The source data
can be mirrored horizontally or vertically or both. Overlay data comes from a buffer located in system
memory. Additionally, the overlay engine can be quadruple buffered in order to support flipping between
different overlay images. Data can either be transferred into the overlay buffer from the host or from an
external PCI adapter, such as DVD hardware or video capture hardware. Buffer swaps can be done by
the host and internally synchronized with the display VBLANK.
The internal graphics device of the GMCH2-M can accept line widths up to 720 pixels. In addition,
overlay source and destination ChromaKeying are also supported. Overlay source/destination
ChromaKeying enables blending of the overlay with the underlying graphics background. Destination
color/chroma keying can be used to handle occluded portions of the overlay window on a pixel by pixel
basis, which is actually an underlay. Source color/chroma keying is used to handle transparency based on
the overlay window on a pixel by pixel basis. This is used when “blue screening” an image in order to
overlay the image on a new background later.