L64105 LSI Logic Corporation, L64105 Datasheet - Page 307

• Manufacturer Part Number: L64105
• Description: Mpeg-2 Audio/video Decoder
• Manufacturer: LSI Logic Corporation

Next, the host must set the Display Override Luma and Chroma Frame
Store Start Addresses. These are the DMA SDRAM Target addresses
the host used for the two stores or the Luma and Chroma Base
Addresses for a decoded picture.
In addition to the address pointers, the host must also program the width
of the image using the Override Picture Width field. The picture
width register has a resolution of 8 pixels, hence the frame store image
width must be in 8-pixel increments. This picture width register is used
by the Display Controller for accessing subsequent lines of the frame
store.
To display a still picture it stored, the host adjusts the main display area
if necessary, sets or clears the Host Top Field First bit as desired, enters
the Decode Stop Command, and sets the Display Override Mode. The
Video Decoder may be left running during the still display.
Display override has two modes, field and frame. Field Mode is provided
for field structure pictures where motion between the fields may cause
distortion of the image. In Field Mode, the first field is controlled by the
Host Top Field First bit and is output during both field times. In Frame
Mode, both fields are output to the display.
When enabled, the still image is processed through the horizontal and
vertical filters of the Video Decoder. The override picture width and the
main reads per line are separate registers and allows the flexibility of
displaying a portion of the still image frame store (necessary for pan and
scan scaling of a still frame).
When the Display Controller is programmed for still image display, the
data is simply read from the Display Override Frame Stores instead of
the frame store indicated by the video decode engine. The parameters
for the Display Override Frame Stores are sampled internally at every
field boundary, allowing the host to change the values in the middle of
the field.
It is possible to display a still image and continue to decode video in the
background. As long as the decoder is started and freeze is not active,
the Display Controller continues to issue decode signals to the decoder.
When a freeze is issued, the Display Controller temporarily suspends
decoding while the freeze is active. This property can be exploited for
various trick modes that require random access.
Still Image Display
9-15