
5-22
External Memory Interface
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
5.5.2
Audio PES
Buffer
The Audio PES buffer stores the PES header information that corre-
sponds to Audio PES packets when the L64005 is programmed to be in
the MPEG-2 PES mode. This buffer stores all the header information that
corresponds to audio that is above the sequence header in the MPEG
layered structure. If the L64005 is programmed to be in MPEG-1 system
mode or MPEG-2 program mode, then the system header information for
both Video and Audio are stored in this buffer. All the header information
above the sequence layer in the MPEG layered structure is in this buffer.
If only MPEG-1 system or MPEG-2 program modes are used, then the
Video PES buffer and the Audio PES buffer may be at the same
addresses—that is, they may occupy the same space in the DRAM.
5.5.3
Video Channel
Buffer
In any mode of operation of the L64005—MPEG-2 PES, MPEG-1 sys-
tem, and MPEG-2 program and video elementary—the video channel
buffer contains the MPEG compressed video data starting from the
sequence header and below. The sequence headers, GOP headers, and
picture headers, along with the compressed data are stored in this buffer.
This header information is also available in the auxiliary data FIFO,
5.5.4
Audio Channel
Buffer
In any mode of operation of the L64005—MPEG-2 PES, MPEG-1 sys-
tem, and MPEG-2 program and audio elementary—the audio channel
buffer contains the MPEG compressed audio data starting from the start
codes and below. The start codes and the compressed data are stored
in this buffer.
The size of all the four channel buffer sections should be dened such
that no overow or underow of data occurs. Ideally, the VBV buffer size
in the ISO/IEC MPEG specication should dene the size of the channel
buffers. All of these channel buffer sections are cyclic in nature which
means that the pointers wrap around after reaching the last address. An
overrun occurs when data is not read out of the channel buffer quickly
enough and the new data is lost. The effect of an overrun on the video
channel buffer is the noticeable the tearing of a picture on the TV moni-
tor. If an overrun occurs on the PES buffers, then the PES header infor-
mation is lost.