
L64005 MPEG-2 Audio/Video Decoder Technical Manual
7-1
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
Chapter 7
Audio Decoder
Chapter 7 describes the details of the integrated, two-channel MUSICAM
(MPEG) audio decoder. This chapter contains the following sections:
7.1
Audio Decoder
Overview
The L64005 integrates a two-channel MPEG audio decoder that is com-
patible with Layer 1 and Layer 2 of the MPEG audio standard. It can
decode audio data with channel bit rates from 8 kbps to 448 kbps in
mono, dual mono, stereo, and joint stereo modes. It accepts a 5.1 chan-
nel audio bitstream and decodes two channels for output. The output
sample rate can be 48 kHz, 44.1 kHz, 32 kHz, 24 kHz, 22.05 kHz or 16
kHz. The decoder takes data from a channel buffer, which is imple-
mented in the DRAM attached to the L64005. The decoder then parses
the data and decompresses it. Finally, it presents the decoded PCM
audio data over a serial DAC interface.
7.2
Decoder
Programming
The L64005 reads all the parameters required for decoding from the
coded channel data. However, the host CPU must program the mode of
the DAC interface and parameters that control the audio sample rate.
The sample rate must be programmed externally.
7.2.1
Reading the
Audio
Parameters
The coded MPEG audio stream contains a number of parameters that
describe the stream. These include the coding rate, bit rate, sampling fre-
quency and copyright information. An external device can read these
data shortly after the decoder parses the audio frame header. The
decoder provides an Audio Sync Code Detect interrupt to indicate when
the data can be read. Note that this data may change every audio frame,
so it must be read after the Audio Sync Code Detect interrupt and before
the next interrupt. Group 6, Register 52 and 53 store only 16 bits of the