3 code overlays – Cirrus Logic CS470xx User Manual
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DS787PP9
3 Code Overlays
3 Code Overlays
The suite of software available for the CS470xx family consists of an operating system (OS) and a library of overlays. The
software components for the CS470xx family include:
1. OS/Kernel—Encompasses all non-audio processing tasks, including loading data from external serial memory,
processing host messages, calling audio-processing subroutines, error concealment, etc.
2. Decoder—Any module that performs a compressed audio decode on IEC61937-packed data delivered via S/PDIF
Rx or I²S input, such as Dolby Digital (AC3).
3. Matrix-processor—Any Module that performs a matrix decode on PCM data to produce more output channels than
input channels (2Æn channels). Examples are Dolby
®
Pro Logic
®
IIx and SRS Circle Surround II
®
. Generally
speaking, these modules increase the number of valid channels in the audio I/O buffer.
4. Virtualizer-processor—Any module that encodes PCM data into fewer output channels than input channels (nÆ2
channels) with the effect of providing “phantom” speakers to represent the physical audio channels that were
eliminated. Examples are Dolby Headphone
®
2 and Dolby
®
Virtual Speaker
®
2. Generally speaking, these
modules reduce the number of valid channels in the audio I/O buffer.
5. Post-processors—Any module that processes audio I/O buffer PCM data. Examples are bass management, audio
manager, tone control, EQ, delay, customer-specific effects, and any post-processing algorithms available for the
CS470xx DSP.
The bulk of standard overlays are stored in ROM within the CS470xx, but a small image is required to configure the
overlays and boot the DSP. This small image can either be stored in an external serial flash/EEPROM, or downloaded via
a host controller through the SPI/I²C serial port.
The overlay structure reduces the time required to reconfigure the DSP when a processing change is requested. Each
overlay can be reloaded independently without disturbing the other overlays. For example, when a different post-processor
is selected, the OS, does not need to be reloaded—only the new post-processor.
lists the different configuration options available. Refer to the CS470xx Firmware User’s Manual for the latest
listing of application codes and Cirrus Framework™ modules available. See
, which provides a summary of the
available channels for each type of input and output communication mode for members of the CS470xx family of DSPs.