
L64005 MPEG-2 Audio/Video Decoder Technical Manual
8-5
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
ers at the end of the PES header and writes them to the appropriate sys-
tem stream buffer.
8.2
Reading the
System Header
Data
In the PES decoding mode (when SSEL[1:0] is set to 002), the L64005
parses system header data and writes it into one of two system channel
the SSEL[1:0] eld. The decoder needs two buffers when parsing a
transport stream so that the audio and video system header data does
not get mixed up with data received from different streams. An external
microprocessor may read these buffers on demand and perform any
additional parsing. Use the DRAM read-through interface to read the
buffers.
In the system (MPEG-1) or Program (MPEG-2) decoding mode (when
SSEL[1:0] is set to 012), both audio and video headers are stored in the
audio PES Buffer. This is because the decoder always receives either a
complete audio or a complete video packet, and there is no possibility of
mixing the packets.
The presence of the start code indicates the beginning of each header
to the external controller. The data that follows the header conforms to
MPEG syntax (with stufng removed from MPEG-1 packets). The last
entry of packet or PES packet headers indicates the value of the elemen-
tary stream write pointer at the time the header was written. This value
allows the decoder to associate the packet header data with the elemen-
tary stream data for synchronization purposes.
Table 8.2 shows an example of a packet header structure and its asso-
ciated write pointer in the Elementary Stream.
8.2.1
System Parser
Control Bits
The following table shows the locations of the bits that control the system
System Parser Control Bits
Register
Stream Select
Group 5, Control Register 0
Header Interrupts
Group 4, Interrupt Register 1
Video System Write Address
Group 7, Register 32, 38, and 39
Audio System Write Address
Group 7, Register 33, 38, and 39