User`s manual

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 (2Ön 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 (nÖ2 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).