Cirrus Logic CS485xx - Manual (Page 13)

1-5 Copyright 2009 Cirrus Logic, Inc. 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
rd
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 Ö 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
Ö 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 ™ /I 2 C ™ 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).