
L64005 MPEG-2 Audio/Video Decoder Technical Manual
4-7
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
Errors and the Decoded Bitstream – When the decoder ags an error,
it continues to decode data at the channel rate up to the next appropriate
resync code for this layer. The internal microcontroller then determines
the error masking strategy. After an error, or if the decoder is not syn-
chronized, the post-parser reads data at one byte (8 bits) per cycle until
the decoder reacquires synchronization. Note that error conditions can
cause data to be read very fast and may cause underow while search-
ing for start codes.
Signalling of Decoded Bitstream Errors – The user may read the sta-
tus of the bitstream error ags at any time. A mask word can be set, indi-
cating whether the error ags generate an interrupt.
Video Sequence Layer – The L64005 synchronizes on the rst
sequence start code that it nds in the bitstream. Assuming no errors,
the L64005 periodically resynchronizes on subsequent sequence start
codes.
Errors either found in the bitstream syntax or signalled from the channel
during the processing of the Video Sequence Layer header are not
maskable, and are agged as Decode Errors
. This includes errors
detected during the processing of user data. The decoder must wait for
a new sequence start code to recover from errors.To detect errors, the
host can decode additional data in the sequence header. Duplicated
sequence headers in the MPEG bitstream, while not compliant, do not
ag errors in the L64005.
Group of Pictures Layer – The L64005 enters the Group of Pictures
Layer from the Video Sequence Layer only if the device is synchronized
to the Video Sequence Layer and no errors have been detected. If the
device is not synchronized to the Video Sequence Layer, spurious start
codes do not cause the decoding of data within the Group of Pictures
Layer.
Errors found in the bitstream syntax, or signalled from the channel during
the processing of the Group of Pictures Layer header, are not maskable
and are agged as Decode Errors. The decoder must wait for a new
sequence start code or group of pictures start code to recover from
decode errors.