L64105 LSI Logic Corporation, L64105 Datasheet - Page 212

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

6.3.4 Preparsing an MPEG-1 System Stream
6-16
In addition to audio and video channel buffers, a System Channel Buffer
is allocated in SDRAM for MPEG-1 streams. This buffer is used to hold
headers. When the decoder encounters any System Start Code, it
synchronizes to that start code, if it is not already in sync. The Preparser
then moves the system header into the System Channel Buffer and looks
for the beginning of the first packet.
Figure 6.8
System Stream
The data flow is shown in
multiplexed in the stream, only the AREQn and AVALIDn are used. When
the Preparser recognizes a Packet Start Code, it checks to see whether
the packet contains audio or video data, and whether the Stream Select
field matches the Stream Select code written into Register 7
by the host. If the Preparser does not find a match, it discards the packet.
For accepted packets, the Preparser uses the Packet Length field to
determine where the packet ends. This is necessary to avoid mistakenly
parsing the possible emulation of start codes in audio packet data.
If the stream ID indicates an audio stream, the Preparser skips any
packet stuffing bytes and moves the remainder of the packet header into
the System PES Channel Buffer. The chip sets the Audio PES Data
Ready Interrupt (Register 2,
signal, if the interrupt is not masked, to indicate to the host that the
packet header is in the System Channel Buffer. The Preparser then
samples the current write pointer for the Audio ES Channel Buffer and
moves its value into the System Channel Buffer after the packet header.
Channel Interface
AVALIDn
MPEG-1
AREQn
Preparsing an MPEG-1 System Stream
Preparser and
Write FIFO
L64105
Figure
page
6.8. Since audio and video packets are
4-6) and asserts the INTRn output
Video ES Channel Buffer
Audio ES Channel Buffer
Channel Buffer
SDRAM
System
(page
4-11)