L64105 LSI Logic Corporation, L64105 Datasheet - Page 244

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

A block diagram of the Video Decoder Module is shown in
Figure
8.1.
The module includes a Channel Read FIFO, Postparser, IDCT Pipeline,
and the Auxiliary and User Data FIFOs and their controller. The
microcontroller is also included since it decodes for the Postparser and
controls most of the data transfers.
The Channel Interface, described in
Chapter
6, parses pack, system, and
packet headers from the bitstream and stores video packet payloads in
the Video ES Channel Buffer in SDRAM. The preparsed video data is
read from the Video ES Channel Buffer into the Channel Read FIFO.
The Postparser, along with the microcontroller, strips the bitstream apart,
and passes the appropriate bits and fields in the stream to the
microcontroller for use in picture decoding, to the Auxiliary Data FIFO
and User Data FIFO for processing by the host, and to the IDCT (Inverse
Discrete Cosine Transform) Pipeline for picture data decoding and
reconstruction. The Postparser decodes layers of syntax starting from the
sequence layer and going through all the lower layers including the group
of pictures layer, picture layer, slice layer, macroblock layer, and block layer.
Table 8.1
through
Table 8.11
define the postparsing operation.
The IDCT Pipeline decodes the block layer bytes per instructions from
the microcontroller decoded from the bitstream. The results are placed
in the frame stores of SDRAM as picture bitmaps. The Video Interface,
described in
Chapter
9, reads the picture data from SDRAM, mixes it
with OSD video and sends the mix to the external NTSC/PAL Encoder.
The Auxiliary Data FIFO is used to store certain parameters from each
of the layers of syntax. The data in the FIFO is available through a
register for the host to read. In general, this data is useful in controlling
the decoder. The User Data FIFO is used to store data that follows the
user data start code in the MPEG-1/2 bitstream. User data also is
available to the host through a register.
Some limited error detection is possible in the syntax and grammar
parsing of an MPEG bitstream. Illegal transitions out of variable length
decode trees and illegal grammars are detected. Usually, it is not
appropriate to continue decoding once the first error in a given layer has
been detected. Resync codes are used to try to establish
synchronization as soon as possible after an error and to limit the
propagation of errors. Resync is achieved by searching for the next start
code of the appropriate layer in the bitstream. This approach of resyncing
8-2
Video Decoder Module