
Preparser
6-17
The host can subsequently use this value for system synchronization.
The Preparser then moves the packet payload into the Audio ES Channel
Buffer. The Preparser uses the Packet Length field in the packet header
to determine the end of the audio data payload.
If the stream ID is a video stream, the Preparser skips any packet
stuffing bytes and moves the remainder of the packet header into the
System Channel Buffer. INTRn is asserted if not masked and the Video
PES Data Ready Interrupt (Register 2,
page 4-6
) is set. The Preparser
then samples the current write pointer for the Video ES Channel Buffer
and stores its value in the System Channel Buffer after the packet
header. The Preparser then moves the packet payload into the Video ES
Channel Buffer. Note that the Preparser must be able to parse the packet
header because there is no header length field.
Figure 6.9
shows the mapping of the header data and payload pointers
in the System Channel Buffer. The header data is written into the buffer
in 64-bit words (four 16-bit bursts). The 20-bit pointers are aligned to the
MSB and preceded by 44 zero bits to round out the word.
Figure 6.9
System PES Channel Buffer Map for MPEG-1 Streams
or
or
63
0
System Header Data (24 bytes)
63
20 19
0
Audio PES Header Data
Stuffing Bits
All 0’s
Audio Pointer (20 bits)
63
20 19
0
Video PES Header Data
Stuffing Bits
All 0’s
Video Pointer (20 bits)