2/24/2008 9T6WP
Preliminary Hardware Data Module
BCM7405
06/29/07
Functional Description
Bro a d c o m Co rp o r a ti o n
Document
7405-1HDM00-R
Advanced Audio Module Page 1-35
O
VERVIEW
OF
A
UDIO
M
ODULE
The BCM7405 audio core consists of DSP subsystem (RPTD) and audio input/output module (AIO). The RPTD is a DSP
system block for decompression of MPEG, Dolby Digital, MPEG-2 AAC, MPEG-4 AAC, and Dolby Digital Plus audio
services. The DSP system also supports a second digital audio path that allows simultaneous output of a digital audio service
in compressed form on SPDIF. All codec processing is performed by the audio firmware in the DSP system. The audio input/
output module consists of: I
2
S input, buffer block (BF), sample rate converter (SRC), data path (DP) and input/output path
(IOP). I
2
S input can be captured by the buffer block and store in SDRAM to provide a time delay with optional adaptive rate
filtering. The PCM data then can be playback to any of the audio outputs (DAC, SPDIF, or I
2
S output).
The buffer block is responsible for playback of up to eight streams from SDRAM. It can also capture up to four streams to
SDRAM. The playback streams can come from the DSP (decoded stream or compressed), I
2
S input, or host (sound effect).
Each playback buffer (PB) or capture buffer (CAP) can have up to two ring buffers
.
A PB or CAP will use one ring buffer if
the left/right data are interleaved or two ring buffer if the data are not interleaved. The compressed stream should use only
one ring buffer instead of two.
The SRC block can sample-rate-convert a stream (left and right PCM) via a high-fidelity SRC or a low-fidelity linear
interpolator. The SRC block can process up to 12 streams.
The data path block is for mixing and multiplexing. It supports up to 32 input streams to eight mixers. Each mixer can be
scaled and mixed up to eight stream inputs. It then can perform soft limiting and volume control on the mixer outputs. Soft
limiting protects mixer data output from being saturated. Each mixer can have up to two outputs with independent volume
control. The user can independently control left and right volume output with ramping for volume changes.
Several output options exist independent of the audio source. The audio data can be output in analog format through the
stereo DAC block. The audio can be output over the I
2
S for connection to an off-chip DAC, or the audio can be output on
SPDIF for digital connection to an A/V amplifier/receiver. In addition, audio can be output to the RF modulator and HDMI.
The Micro-Sequencer (MS) handles the bit stream packing for the SPDIF output.
The IOP has one SPDIF output which can output either PCM or compressed data. It has one stereo DAC output and one
I
2
S output. There is also one spare I
2
S output which shares with I
2
S input. IOP can capture data from I
2
S input. The captured
data is transferred to the buffer block to be stored in SDRAM. The PCM data from down stream can also loop back to BF
capture for additional post processing when required. The loop back rate should be the same at the stream sample rate.
