2 code overlays – Cirrus Logic CS485xx User Manual

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1-5

DS734UM7

Code Overlays

CS485xx Hardware User’s Manual

This chip, teamed with Cirrus digital interface products and mixed-signal data converters, enables the design
of next-generation digital entertainment products.

Licenses are required for all of the 3

party audio processing algorithms listed in

"Code Overlays"

. Please

contact your local Cirrus Logic Sales representative for more information.

1.2 Code Overlays

The suite of software available for the CS485xx family consists of an operating system (OS) and a library of
overlays. The overlays have been divided into three main groups called Matrix-processors, Virtualizer-
processors, and Post-processors. All software components are defined below:

•

OS/Kernel - Encompasses all non-audio processing tasks, including loading data from external
memory, processing host messages, calling audio-processing subroutines, error concealment, etc.

•

Matrix-processor- Any Module that performs a matrix decode on PCM data to produce more output

channels than input channels (2

n channels). Examples are Dolby

ProLogic

IIx and DTS

Neo:6

. Generally speaking, these modules increase the number of valid channels in the audio I/O

buffer.

•

Virtualizer-processor - Any module that encodes PCM data into fewer output channels than input
channels (n

2 channels) with the effect of providing “phantom” speakers to represent the physical

audio channels that were eliminated. Examples are Dolby Headphone

and Dolby

Virtual

Speaker

. Generally speaking, these modules reduce the number of valid channels in the audio I/O

buffer.

•

Post-processors - Any module that processes audio I/O buffer PCM data in-place after the matrix- or
virtualizer-processors. Examples are bass management, audio manager, tone control, EQ, delay,
customer-specific effects, etc.

The bulk of each overlay is stored in ROM within the CS485xx, 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

™

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 new matrix-processor is selected, the OS, virtualizer-, and post-processors do not need to be
reloaded — only the new matrix-processor (the same is true for the other overlays).