Introduction to Audio Device Driver Programming Guide

This book describes the architecture, services, and mechanisms of the I/O Kit’s Audio family, and explains how you use the APIs of the family to write an audio device driver for OS X. It does not cover any aspect of user-space audio programming (MIDI, synthesizers, CD players, and so on) except to discuss the overall composition of the OS X audio system, which includes Core Audio and other audio frameworks.

To gain the most value from reading this book, it helps to be familiar with the I/O Kit and object-oriented programming, preferably C++ programming. The book IOKit Fundamentals provides a thorough introduction to the I/O Kit; see Additional Information on the I/O Kit for details on this and other I/O Kit documentation.

Who Should Read This Document?

As with any kernel-level device driver, you should only write a driver if there is no other way to achieve your goals. Many audio devices are supported natively in OS X. If your device complies with USB or FireWire audio standards, you should not need to write a custom driver unless you need to implement features beyond those supported in the relevant audio standards.

In some cases, even if you need to do special device-specific processing, you may be able to do so without writing an entire driver. For example, some USB audio hardware (for USB speakers, for example) may require additional software filtering, such as equalization. OS X provides a mechanism in the kernel for doing this through the AppleUSBAudio plug-in model. For more information, see the SampleUSBAudioPlugin example code.

Organization of This Document

This document describes all aspects of creating an audio device driver using the I/O Kit’s Audio family. It includes conceptual and procedural information and consists of the following chapters:

• Audio on OS X—Describes the features, benefits, and architecture of the OS X audio system. It includes an overview of the audio I/O model.

• Audio Family Design—Presents a comprehensive overview of the Audio family’s architecture, classes, object relationships, and primary mechanisms. It also goes into more detail about the workings of the audio I/O model in OS X.

• Implementing an Audio Driver—Describes the various steps required to design and implement an audio device driver using the Audio family. Most steps are amply illustrated with sample code.

For details of specific methods, structures, and other API elements, consult the reference documentation for the Audio family. See Additional Information on the I/O Kit for instructions on accessing this documentation.