L64105 LSI Logic Corporation, L64105 Datasheet - Page 286

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

display happen to coincide. When the decoder is set for Rip Forward
Mode, the internal automatic rate control is turned off since the intention
is to reconstruct pictures as fast as possible.
Figure 8.8
shows examples
when rate control is applied on B picture and on anchor picture
reconstruction.
The host can force rate control on for all pictures by setting the Force
Rate Control bit in Register 239
(page
4-55). In this mode, the decoder
always checks for reconstruction overrunning display based on the lines
currently displayed. When this bit is cleared (normal mode), the
reconstruction overrunning display check is only performed if the decoder
is reconstructing over the top of the same physical frame store that is
currently being displayed (i.e., the last field of the frame store is being
displayed and the next picture is being reconstructed in the same frame
store). It is recommended that this bit be set only during trick modes
where the host software is changing the address of the frame stores in
SDRAM dynamically. An example is Display Override Mode where the
host is changing the frame store pointers (A1, A2, and A3) at the start
of every picture reconstruction to point to different physical locations in
SDRAM. In modes like this, the host should set the Force Rate Control
bit since the Video Decoder may not automatically detect that rate control
is needed. During the Rip Forward Mode, the internal rate control is
turned off. If the host displays selective reconstructed pictures, it should
force rate control on for certain fields.
Figure 8.9
shows an example of
how the Force Rate Control bit is used in Rip Forward Mode.
8-44
Video Decoder Module