L64005 MPEG-2 Audio/Video Decoder Technical Manual
1-27
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
1.6.6.5 Channel Data Writes
Channel data can be written directly through the system controller inter-
face instead of through the serial channel interface. Direct writing sup-
ports the parallel interfaces that are found in computer systems,
particularly CD-ROM players. An internal control bit selects the
serial/parallel mode. It is the user’s responsibility to ensure that writes to
the parallel channel interface do not exceed the channel rate. State bits
are provided that allow the user to poll the busy status of the audio and
video channel. Output pins are also provided that reects this status.
These pins are used where a hardware handshake is needed.
1.6.7
Channel
Interface
Coded bitstream data is typically written serially into the L64005. On
each rising edge of a serial channel clock, the decoder reads a single bit
and an associated data-valid signal. The peak sustained rate on the
serial interface is a function of the device clock. At the nominal frequency
of 27 MHz, this rate is 20 Mbits/second. The instantaneous burst rate on
the serial channel is faster and a function of device characterization. The
burst rate limits the packet length and packet separation in a variable
channel rate system.
Synchronization circuitry in the channel interface allows the device clock
and the channel clock to run at different rates. The coded MPEG data
does not need to be byte aligned in the stream.
1.6.8
Bitstream
Syntax and
Grammar
The L64005 operates on MPEG-2 bitstream syntax. The device can
decode either an MPEG-2 or MPEG-1 video sequence layer. If presented
with an MPEG-1 System Layer bitstream, the L64005 parses out and
decodes the Packet Layer and the Video Sequence Layer inside—which
may be either an MPEG-1 or MPEG-2 stream.
1.6.8.1 User Data
User data in the channel is buffered on-chip and may be read by the sys-
tem controller. The on-chip user data FIFO is intended to buffer data until
the system controller can service an interrupt and read the data. If the
data is not read, the FIFO overows and all user data in the FIFO is
invalidated until the user data FIFO is reset. It is the responsibility of the
system controller to act on user data when appropriate.