L64105 LSI Logic Corporation, L64105 Datasheet - Page 322

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

9.9.2.5 Bits/Pixel Modes
9.9.2.6 OSD Controller Operation
9-30
The OSD Controller reads the OSD data from the SDRAM frame stores
and displays it at a rate of one pixel every two L64105 clocks. Using
6 bits for Y, and 4 bits each for Cb and Cr, the OSD color palette can
contain any of 16,384 colors including black and transparent. The Cb and
Cr values are decimated from 4:4:4 to 4:2:2 prior to mixing with the
decoded video data. As indicated, the pixels can be coded using 2, 4, or
8 bits to produce 4, 16, or 256 YCbCr color values.
The color palette may be updated once per OSD area. The OSD
controller automatically performs this process prior to displaying the next
OSD area. This color expansion feature allows many more colors to be
displayed on the overlay screen at one time.
Since the palette contains 256 colors in 8 bits/pixel mode, the palette
should be loaded only once per field with the first OSD area of the frame.
The data for subsequent OSD areas should include only the header
control information and the area bitmap.
At the beginning of each field, the OSD Controller scans the display list
stored in SDRAM and loads the first 64 bits (header control information)
for the first OSD area into the internal OSD control registers. The OSD
Controller then buffers the color palette information and bitmap data, and
waits until the Display Controller output reaches the first pixel location of
the OSD area (defined in the STARTR and STARTC fields of the header).
It mixes the OSD data with the reconstructed video data according to the
mix weight in the header and the mix enable in the color palette. When
the OSD Controller outputs the last line of the OSD area, it immediately
loads the next 64 bits of header information from the display list and the
process repeats itself. Only one OSD area is active at a time and multiple
areas cannot lie on the same horizontal line.
Video Interface