L64105 LSI Logic Corporation, L64105 Datasheet - Page 311

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

9.7 Reduced Memory Mode
For applications where SDRAM space is limited, Reduced Memory Mode
(RMM) may be enabled to reduce the memory required for B-frame
reconstruction. RMM is intended for applications with PAL resolution
images, or when large OSD display areas limit the availability of SDRAM.
Since RMM overwrites the memory used for decoding the first field of the
B frame immediately after display, only a subset of the display modes
and features are available for use in RMM. The available display modes
include 4, 5, 6, 7, 8, 10, and 11. However, since display modes 4 and 5
repeat the entire field of chroma during the second field time, only luma
data can utilize the benefits of the reduced memory frame store. Care
must be taken to allot enough memory for the entire frame of chroma.
Reduced Memory Mode
Display Mode 7 - Interlaced Luma/Interlaced Chroma with
Repositioning. Both the luma data and chroma data are treated as
interlaced. The chroma data is filtered using the bilinear chroma filter
to improve the chroma positioning. This display mode is suited for
either field- or frame-structured pictures.
Display Mode 8 - Interlaced Luma/Interlaced Chroma 0.75
Letterbox Filtering. Both the luma and chroma data is treated as
interlaced and processed through the letterbox filter to achieve
decimation of four lines down to three. The main start and end rows
must be adjusted to account for this 0.75 decimation. The total
number of lines per field should be adjusted according to the
following equation:
Display Mode 11 (0xB) - Interlaced Luma/Interlaced Chroma 0.5
Letterbox Filtering. Both the luma and chroma data is treated as
interlaced and processed through the letterbox filter to achieve
decimation of four lines down to two. The main start and end rows
must be adjusted to account for this 0.5 decimation. The total
number of lines per field should be adjusted according to the
following equation:
Main End Row - Main Start Row + 1 = (0.75 * lines/field) - 2
Main End Row - Main Start Row + 1 = (0.5 * lines/field) - 2
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