Architecture; Alsa Soc Layer; Design - Texas Instruments OMAP35 Series User Manual

5.3. Architecture

5.3.1. ALSA SoC Layer

The overall project goal of the ALSA System on Chip (ASoC) layer is to provide
better ALSA support for embedded system on chip procesors and portable audio
codecs. Currently there is some support in the kernel for SoC audio, however
it has some limitations:
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5.3.2. Design

The ASoC layer is designed to address these issues and provide the following
features:
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To achieve all this, ASoC basically splits an embedded audio system into three
components:
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Currently, codec drivers are often tightly coupled to the underlying SoC cpu.
This is not really ideal and leads to code duplication.
There is no standard method to signal user initiated audio events.
e.g. Headphone/Mic insertion, Headphone/Mic detection after an insertion
event.
Current drivers tend to power up the entire codec when playing (or
recording) audio. This is fine for a PC, but tends to waste a lot of power on
portable devices. There is also no support for saving power via changing
codec oversampling rates, bias currents, etc.
Codec independence: Allows reuse of codec drivers on other platforms and
machines.
Easy I2S/PCM audio interface setup between codec and SoC. Each SoC
interface and codec registers it's audio interface capabilities with the core
and are subsequently matched and configured when the application hw
params are known.
Dynamic Audio Power Management (DAPM): DAPM automatically sets the
codec to it's minimum power state at all times. This includes powering up/
down internal power blocks depending on the internal codec audio routing
and any active streams.
Pop and click reduction: Pops and clicks can be reduced by powering the
codec up/down in the correct sequence (including using digital mute). ASoC
signals the codec when to change power states.
Codec driver: The codec driver is platform independent and contains audio
controls, audio interface capabilities, codec dapm definition and codec IO
functions.
Platform driver: The platform driver contains the audio dma engine and
audio interface drivers (e.g. I2S, AC97, PCM) for that platform.
Platform Support Products
Audio Driver
Architecture
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