Sitara Linux Audio Introduction

Linux Software Developer's Guide

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Linux Kernel

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Audio

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Introduction

Overview

This diagram gives a visual explanation of the hardware and software components that make audio possible in linux on Sitara processors.

This section provides a high level overview of the hardware and software elements that are required for audio related functionality on Sitara processors.

System Overview

Though various hardware and software configurations are used on Sitara EVMs, there are a common set of elements that must be properly set up so that audio is enabled in linux. They are as follows:

• An external audio capture or playback device (such as ADCs, DACs, audio codecs, or even network devices)
• A Sitara data interface (such McASP or USB) that can communicate with that external audio device
• The linux audio framework (ALSA)
• An ALSA compatible driver for the selected external audio device

Multimedia frameworks, such as GStreamer, can sit on top of the ALSA driver and allow for more advanced features, but are not required for basic usage.

Hardware Components

The most common hardware component on Sitara processors that is used to enable audio is the McASP, which provides an I2S interface that can be connected to external audio device, such as the AIC3106 codec that is used on many Sitara EVMs.

USB audio dongles are another common way of providing hardware audio capability; linux by default provides an extensive amount of driver support for USB audio devices, which in many cases may make them easier to integrate into a system than an I2S solution.

Network audio sources are yet another way for linux to transmit and receive audio data. These are possible through a number of hardware elements, such as Ethernet, USB Wifi Dongles, and MDIO based Wifi chips.

Software Components

Regardless of the hardware being used, linux uses one standard architecture for all audio support: ALSA.  ALSA consists of kernel drivers and a user-space API that allows for the creation of audio applications.

Any audio hardware device that is connected linux must have an ALSA compatible driver in order for it to be accessible; for instance, AIC3x codecs present on Sitara EVMs have such an ALSA based driver. For USB audio dongles, configuring the ALSA driver is often quite simple; when plugged into a USB port, linux will automatically detect the device and configure it as an ALSA device.

The linux community has produced a host of powerful software libraries, frameworks, and applications that greatly expand the audio possibilities of linux. Two of these that are included within the Sitara SDK filesystem are GStreamer and PulseAudio. GStreamer is a flexible multimedia framework that can be used to prototype audio playback and capture for various usecases, and PulseAudio is a sound server that allows for mixing, network audio, and a number of others.

Acronyms & Definitions

Acronym	Definition
ALSA	Advanced Linux Sound Architecture
ALSA SoC	ALSA System on Chip
DMA	Direct Memory Access
I2C	Inter-Integrated Circuit
McASP	Multi-channel Audio Serial Port
PCM	Pulse Code Modulation
TDM	Time Division Multiplexing
OSS	Open Sound System
I2S	Inter-IC Sound

Archived Versions

Sitara Linux SDK 08.00.00.00