IEC 62680-1-6:2019

Universal serial bus interfaces for data and power - Part 1-6: Common components - USB Audio 3.0 device class definition basic functions

The purpose of IEC 62680-1-6:2019 is to create a higher level of interoperability among Hosts and Audio Devices. By establishing a set of essential audio features, users can expect a consistent experience, Device manufacturers have a solid template to follow, and Host drivers may be simplified.
The USB Audio Device Class Definition for Basic Audio Functions applies to all USB Audio Functions that are based on the Universal Serial Bus Device Class Definition for Audio Devices Release 3.0. It defines baseline audio functionality for all ADC 3.0 compliant Hosts and Devices.

Interfaces de bus universel en série pour les données et l'alimentation électrique - Partie 1-6: Composants communs - Définition de classes de dispositifs USB Audio 3.0 pour fonctions de base

L'IEC 62680-1-6:2019 a pour objectif de créer un niveau d'interopérabilité plus élevé entre les hôtes et les dispositifs audio. En établissant un ensemble de fonctions audio essentielles, les utilisateurs peuvent s'attendre à une expérience cohérente, les fabricants d'appareils disposent d'un solide modèle à suivre et les pilotes hôtes peuvent être simplifiés.
La définition de classes de dispositifs audio USB pour fonctions audio de base s'applique à toutes les fonctions audio USB reposant sur la version 3.0 de la définition de classes de dispositifs de bus universel en série pour les dispositifs audio. Elle définit les fonctionnalités audio de référence pour tous les hôtes et dispositifs compatibles ADC 3.0.

General Information

• Status: Published
• Publication Date: 18-Sep-2019
• ICS: 29.200 - Rectifiers. Convertors. Stabilized power supply
• ICS: 33.120.20 - Wires and symmetrical cables
• ICS: 35.200 - Interface and interconnection equipment
• Technical Committee: TA 18 - Multimedia home systems and applications for end-user networks
• Current Stage: PPUB - Publication issued
• Start Date: 28-Aug-2019
• Completion Date: 19-Sep-2019

Standards Content (Sample)

IEC 62680-1-6 ®
Edition 1.0 2019-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Universal serial bus interfaces for data and power –
Part 1-6: Common components – USB Audio 3.0 device class definition basic
functions
Interfaces de bus universel en série pour les données et l'alimentation
électrique –
Partie 1-6: Composants communs – Définition de classes de dispositifs USB
Audio 3.0 pour fonctions de base

Copyright © 1997-2016 USB-IF
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IEC 62680-1-6 ®
Edition 1.0 2019-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Universal serial bus interfaces for data and power –

Part 1-6: Common components – USB Audio 3.0 device class definition basic

functions
Interfaces de bus universel en série pour les données et l'alimentation

électrique –
Partie 1-6: Composants communs – Définition de classes de dispositifs USB

Audio 3.0 pour fonctions de base

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 35.200; 29.200; 33.120.20 ISBN 978-2-8322-7242-8

– 2 – IEC 62680-1-6:2019
© USB-IF:1997-2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
UNIVERSAL SERIAL BUS INTERFACES FOR DATA AND POWER –

Part 1-6: Common components –
USB Audio 3.0 device class definition basic functions

FOREWORD
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International Standard IEC 62680-1-6 has been prepared by technical area 18: Multimedia
home systems and applications for end-user networks, of IEC technical committee 100: Audio,
video and multimedia systems and equipment.
The text of this standard was prepared by the USB Implementers Forum (USB-IF). The
structure and editorial rules used in this publication reflect the practice of the organization
which submitted it.
Copyright © 1997-2016 USB Implementers Forum, Inc. All rights reserved.

© USB-IF:1997-2016
The text of this International Standard is based on the following documents:
CDV Report on voting
100/3158/CDV 100/3228/RVC
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
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• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
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© USB-IF:1997-2016
INTRODUCTION
The IEC 62680 series is based on a series of specifications that were originally developed by the USB
Implementers Forum (USB-IF). These specifications were submitted to the IEC under the auspices of
a special agreement between the IEC and the USB-IF.
This standard is the USB-IF publication USB Device Class Definition for Basic Audio Functions
Release 3.0.
The USB Implementers Forum, Inc.(USB-IF) is a non-profit corporation founded by the group of
companies that developed the Universal Serial Bus specification. The USB-IF was formed to provide a
support organization and forum for the advancement and adoption of Universal Serial Bus technology.
The Forum facilitates the development of high-quality compatible USB peripherals (devices), and
promotes the benefits of USB and the quality of products that have passed compliance testing.
ANY USB SPECIFICATIONS ARE PROVIDED TO YOU "AS IS, "WITH NO WARRANTIES
WHATSOEVER, INCLUDING ANY WARRANTY OF MERCHANTABILITY, NON-INFRINGEMENT,
OR FITNESS FOR ANY PARTICULAR PURPOSE. THE USB IMPLEMENTERS FORUM AND THE
AUTHORS OF ANY USB SPECIFICATIONS DISCLAIM ALL LIABILITY, INCLUDING LIABILITY
FOR INFRINGEMENT OF ANY PROPRIETARY RIGHTS, RELATING TO USE OR
IMPLEMENTATION OR INFORMATION IN THIS SPECIFICAITON.
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IEC DOES NOT TAKE ANY POSITION AS TO WHETHER IT IS ADVISABLE FOR YOU TO ENTER
INTO ANY USB ADOPTERS AGREEMENTS OR TO PARTICIPATE IN THE USB IMPLEMENTERS
FORUM.”
Copyright © 1997-2016 USB Implementers Forum, Inc. All rights reserved.

© USB-IF:1997-2016
UNIVERSAL SERIAL BUS
DEVICE CLASS DEFINITION
FOR
BASIC AUDIO FUNCTIONS
Release 3.0
September 22, 2016
Copyright © 1997-2016 USB Implementers Forum, Inc. All rights reserved.

– 6 – IEC 62680-1-6:2019
© USB-IF:1997-2016
SCOPE OF THIS RELEASE
This document is the Release 3.0 of this specification.
CONTRIBUTORS
Joe Scanlon Advanced Micro Devices
Rhoads Hollowell Apple Inc.
Girault Jones Apple Inc.
Matthew X. Mora Apple Inc.
Tzung-Dar Tsai C-Media Electronics, Inc.
Brad Lambert Cirrus Logic, Inc.
Dan Bogard Conexant Systems, Inc.
Pete Burgers DisplayLink (UK), Ltd.
David Roh Dolby Laboratories, Inc.
Leng Ooi Google, Inc.
Pierre-Louis Bossart Intel Corporation
David Hines Intel Corporation
Abdul Rahman Ismail (Co-Chair) Intel Corporation
Devon Worrell Intel Corporation
Chandrashekhar Rao Logitech, Inc.
Terry Moore MCCI Corporation
Alex Lin MediaTek, Inc.
Bala Sivakumar Microsoft Corporation
Geert Knapen (Co-Chair & Editor) NXP Semiconductors
PL Mobile Audio
411 E. Plumeria drive
San Jose, CA 95134, USA
Phone: [phone]
E-mail: [e-mail]
James Goel Qualcomm, Inc.
Andre Schevciw Qualcomm, Inc.
Jin-Sheng Wang Qualcomm, Inc.
Morten Christiansen Synopsys
REVISION HISTORY
Rev. Date Filename Description
1.0 Nov. 24, 09 BasicAudioDevice-10.pdf Release 1.0
3.0 Sep. 22, 16 BasicAudioDevice30.pdf Release 3.0
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© USB-IF:1997-2016
Copyright © 1997-2016 USB Implementers Forum, Inc.
All rights reserved.
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NOTE: VARIOUS USB-IF MEMBERS PARTICIPATED IN THE DRAFTING OF THIS SPECIFICATION. CERTAIN OF
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PROPERTY RIGHTS THAT MAY BE INFRINGED IN THE IMPLEMENTATION OF THIS SPECIFICATION. PERSONS
IMPLEMENT THIS SPECIFICATION AT THEIR OWN RISK.
Dolby™, AC-3™, Pro Logic™ and Dolby Surround™ are trademarks of Dolby Laboratories, Inc.
All other product names are trademarks, registered trademarks, or service marks of their respective owners.
Please send comments via electronic mail to [e-mail]

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– 8 – IEC 62680-1-6:2019
© USB-IF:1997-2016
TABLE OF CONTENTS
Scope of This Release . 6
Contributors . 6
Revision History . 6
Table of Contents . 8
List of Tables . 10
List of Figures . 11
1 Introduction . 12
1.1 Scope . 12
1.2 Purpose . 12
1.3 Related Documents . 12
1.4 Terms and Abbreviations . 12
2 Management Overview. 14
3 Classification . 15
4 General Requirements . 16
4.1 Host and Basic Audio Device Interoperability . 16
4.2 BADD AudioStreaming Interfaces . 16
4.2.1 USB Speeds . 16
4.2.2 Burst Modes . 16
4.2.3 Synchronization Type . 16
4.2.4 Sampling Frequency & Bit Depth . 16
4.2.5 Cluster Descriptors . 16
4.3 Power Considerations . 18
4.3.1 Power Domains . 18
5 Topologies . 19
5.1 BAOF Topology . 19
5.2 BAIF Topology . 19
5.3 BAIOF Topology . 20
6 Descriptors . 22
6.1 Standard Descriptors . 22
6.2 Interface Descriptors . 22
6.2.1 Interface Association Descriptor . 22
6.2.2 AudioControl Interface Descriptors . 22
6.2.3 AudioControl Endpoint Descriptors . 30
6.2.4 AudioStreaming Interface Descriptors . 30
6.3 String Descriptors . 34
7 Requests . 35
7.1.1 Standard Requests . 35
7.1.2 Class-specific Requests . 35
8 BADD Profiles . 37
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© USB-IF:1997-2016
8.1 Generic I/O Profile. 37
8.2 Headphone Profile . 38
8.3 Speaker Profile . 39
8.4 Microphone Profile . 40
8.5 Headset Profile . 40
8.6 Headset Adapter Profile . 41
8.7 Speakerphone Profile . 42

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– 10 – IEC 62680-1-6:2019
© USB-IF:1997-2016
LIST OF TABLES
Table 4-1: Mono Cluster Descriptor . 17
Table 4-2: Stereo Cluster Descriptor . 18
Table 6-3: Interface Association Descriptor . 22
Table 6-4: Standard AC Interface Descriptor . 23
Table 6-5: Class-Specific AC Interface Header Descriptor . 23
Table 6-6: Input Terminal ID1 Descriptor . 24
Table 6-7: Input Terminal ID4 Descriptor . 24
Table 6-8: Output Terminal ID3 Descriptor . 25
Table 6-9: Output Terminal ID6 Descriptor . 25
Table 6-10: Connectors Descriptor . 26
Table 6-11: Connectors Descriptor . 26
Table 6-12: Mixer Unit Descriptor . 27
Table 6-13: Feature Unit ID2 Descriptor . 27
Table 6-14: Feature Unit ID5 Descriptor . 28
Table 6-15: Feature Unit ID7 Descriptor . 28
Table 6-16: Clock Source Descriptor . 29
Table 6-17: Power Domain ID10 Descriptor. 29
Table 6-18: Power Domain ID11 Descriptor. 30
Table 6-19: Standard AC Interrupt Endpoint Descriptor . 30
Table 6-20: Standard AS Interface Descriptor (Alt. Set. 0) . 31
Table 6-21: Standard AS Interface Descriptor . 31
Table 6-22: Class-Specific AS Interface Descriptor . 32
Table 6-23: Standard AS Isochronous Audio Data Endpoint Descriptor . 33
Table 6-24: Class-Specific AS Isochronous Audio Data Endpoint Descriptor . 33
Table 6-25: Standard AS Explicit Feedback Endpoint Descriptor . 33
Table 8-26: Number of Channels . 37
Table 8-27: Generic Profile Descriptor Variables . 38
Table 8-28: Headphone Profile Descriptor Variables . 39
Table 8-29: Speaker Profile Descriptor Variables . 39
Table 8-30: Microphone Profile Descriptor Variables . 40
Table 8-31: Headset Profile Descriptor Variables . 41
Table 8-32: Headset Adapter Profile Descriptor Variables . 42
Table 8-33: Speakerphone Profile Descriptor Variables . 43

Copyright © 1997-2016 USB Implementers Forum, Inc. All rights reserved.

© USB-IF:1997-2016
LIST OF FIGURES
Figure 5-1: BAOF Topology . 19
Figure 5-2: BAIF Topology. 20
Figure 5-3: BAIOF Topology . 21

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– 12 – IEC 62680-1-6:2019
© USB-IF:1997-2016
1 INTRODUCTION
1.1 SCOPE
The USB Audio Device Class Definition for Basic Audio Functions applies to all USB Audio Functions that are
based on the Universal Serial Bus Device Class Definition for Audio Devices Release 3.0. It defines baseline audio
functionality for all ADC 3.0 compliant Hosts and Devices.
1.2 PURPOSE
The purpose of this specification is to create a higher level of interoperability among Hosts and Audio Devices.
By establishing a set of essential audio features, users can expect a consistent experience, Device
manufacturers have a solid template to follow, and Host drivers may be simplified.
1.3 RELATED DOCUMENTS
• Universal Serial Bus Specification, Revision 2.0 (referred to in this document as the USB Specification). In
particular, see Chapter 5, “USB Data Flow Model” and Chapter 9, “USB Device Framework.”
• Universal Serial Bus 3.1 Specification, Revision 1.0 (referred to in this document as the USB 3.1
Specification). This document covers details specific to SuperSpeed and SuperSpeed+ devices.
• Universal Serial Bus Device Class Definition for Audio Devices Release 3.0 (referred to in this document as
Audio 3.0 Specification or ADC 3.0 in short).
• Universal Serial Bus Device Class Definition for Audio Data Formats Release 3.0 (referred to in this
document as Audio 3.0 Data Formats).
• Universal Serial Bus Device Class Definition for Terminal Types Release 3.0 (referred to in this document as
Audio 3.0 Terminal Types).
• Device Class Definition for Human Interface Devices (HID) Version 1.11. June 27, 2001.
• HID Usage Tables Version 1.12. October 28, 2004. Please visit www.usb.org for the latest additions to the
HID Usage Tables.
1.4 TERMS AND ABBREVIATIONS
This section defines terms used throughout this document. For additional terms that pertain to the Universal
Serial Bus, see the “Terms and Abbreviations” section in the USB Specification and for terms that pertain to the
Audio Device Class, see the “Terms and Abbreviations” section in the Audio 3.0 Specification.
Note: the terms “Audio Device” and “Audio Function” are used interchangeably in this document. Since audio
functionality always resides at the interface level, the term Audio Device is strictly speaking omly valid for
devices that contain audio functionality only.
BADD: Acronym for Basic Audio Device Definition.
BAIF: Acronym for Basic Audio Input Function.
BAIFT: Acronym for Basic Audio Input Function Topology.
BAIOF: Acronym for Basic Audio Input/Output Function.
BAIOFT: Acronym for Basic Audio Input/Output Function Topology.
BAOF: Acronym for Basic Audio Output Function.
BAOFT: Acronym for Basic Audio Output Function Topology.
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© USB-IF:1997-2016
Reserved Reserved is a keyword indicating reserved bits, bytes, words,
fields, and code values that are set-aside for future
standardization. Their use and interpretation may be specified
by future extensions to this specification and, unless otherwise
stated, shall not be utilized or adapted by vendor
implementation. A reserved bit, byte, word, or field shall be set
to zero by the sender and shall be ignored by the receiver.
Copyright © 1997-2016 USB Implementers Forum, Inc. All rights reserved.

– 14 – IEC 62680-1-6:2019
© USB-IF:1997-2016
2 MANAGEMENT OVERVIEW
The USB Device Class Definition for Audio Devices is a very rich specification, designed to cover virtually all
Audio Functions and make them controllable via USB. As a result, a generic Audio Device Class driver tends to
become rather complex, as it needs to be able to handle all the mandatory and optional features that are
available in the specification.
For some audio applications where on one hand, the Host capabilities are inherently limited (such as handheld
devices) and on the other hand the peripheral device complexity is limited (such as a headset), it is worthwhile
to create a derived USB Audio Device Class Definition for Basic Audio Functions (this document) or Basic Audio
Device Definition (BADD) in short, based on the existing Audio 3.0 Specification. The Basic Audio Device
Definition defines a subclass specification to which compliant Audio Functions shall adhere. Since the Basic
Audio Device Definition is only defining restrictions and limitations on the existing Audio 3.0 Specification, any
Audio Function that is compliant with the Basic Audio Device Definition is automatically also compliant with the
standard Audio 3.0 Specification.
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© USB-IF:1997-2016
3 CLASSIFICATION
This specification creates the Basic Audio Device Definition (BADD), which is based on, compliant with, and a
subset of the Audio 3.0 specification. It defines a baseline behavior for Basic Audio Functions and contains a set
of rules, normative limitations, and informative descriptions that are applied to the Audio 3.0 specification to
define a specific scope and use for this specification. It does not create new requirements that are not already
part of the Audio 3.0 specification so that any Audio Function that complies with BADD is intrinsically compliant
with the Audio 3.0 specification. In other words, BADD always defines a subset specification and never extends
the Audio 3.0 specification.
BADD defines a number of very specific Audio Functions, called Profiles, each identifiable via a unique Profile
Identifier. The Profile ID is reported via the bFunctionSubClass field of the Interface Association Descriptor.
Once a driver has retrieved that Profile ID, it knows exactly the entire nature and capabilities of the Audio
Function. All class-specific descriptors are fixed by this specification and therefore shall not be included in the
Device’s Configuration descriptor. Only standard USB descriptors for the Audio Function shall be present. Once
a Host driver knows the Profile ID, it needs to refer to this BADD specification for the exact layout of the class-
specific descriptors, based on the identifier and can assume that the BADD Audio Function is built exactly
according to this document.
Device implementations shall not deviate from the Audio Function specification as presented in this document
in any form.
Only three types of Audio Functions are allowed under the Basic Audio Device Definition. These are:
• Basic Audio Output Function (BAOF):
Contains one or more transducers that convert electrical signals into sound. These electrical signals
are generated from digital data streams that are delivered over the USB to the BAOF. Some basic
audio control functionality is also provided.
• Basic Audio Input Function (BAIF):
Contains one or more transducers that convert sound into electrical signals. These electrical signals
are then converted into digital data streams that are delivered over the USB to a Host. Some Basic
audio control functionality is also provided.
• Basic Audio I/O Function (BAIOF):
A combination of a BAIF and BAOF into a single Audio Function. In addition to the components found
in a BAIF and BAOF, a BAIOF also contains a signal path from the input signal path to the output signal
path so that the sound picked up by the audio input can be made audible through the audio output
(Side-tone mixing).
Each BADD compliant Audio Function is based on one or a combination of the above types. This specification
exhaustively defines the allowed combinations as distinct Profiles. For more details on currently defined
Profiles, refer to Section 8, “BADD Profiles.”
General requirements that apply to all Profiles are described in Section 4, “General Requirements”. The
allowed topologies for a BAOF, BAIF, and BAIOF are highlighted in Section 5, “Topologies”. Section 6,
“Descriptors” presents some of the standard descriptors with their specific field values as they apply to a BADD
compliant Device as well as a full set of all possible class-specific descriptors that are needed to describe all of
the supported Profiles. Note that the class-specific descriptors are not implemented into the BADD device but
must be inferred from this specification, based on the Profile ID the BADD Device exposes. Section 7,
“Requests” presents an overview of all possible requests a BADD Device may need to support. Finally, Section
8, “BADD Profiles” provides details about each Profile as defined by this specification.
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– 16 – IEC 62680-1-6:2019
© USB-IF:1997-2016
4 GENERAL REQUIREMENTS
4.1 HOST AND BASIC AUDIO DEVICE INTEROPERABILITY
A Host can claim interoperability with BADD when it supports all BADD Profiles.
BADD Devices shall be constructed in full compliance with this specification and provide all necessary
Configurations as described in the Backwards Compatibility Section of the ADC 3.0 specification.
It is highly recommended that a Basic Audio Function assume default values for all of its settings that provide a
good user experience without the need for prior Host intervention. For example, in the case of a BAIOF, the
Volume Control of the Sidetone Feature Unit (see further) should have a default value (out-of-the-box) such
that a comfortable sidetone level is mixed into the output path.
4.2 BADD AUDIOSTREAMING INTERFACES
All BADD AudioStreaming interfaces shall be of the type USB Streaming. There shall be at most one
AudioStreaming IN interface and at most one AudioStreaming OUT interface. MIDIStreaming intefaces are not
allowed.
4.2.1 USB SPEEDS
A Device that incorporates a BADD compliant Audio Function may support any USB-defined operating speed
that supports isochronous transfers.
4.2.2 BURST MODES
All BADD AudioStreaming interfaces shall at least (besides the mandatory zero-bandwidth Alternate Setting #0)
support an Active Alternate Setting #1 that supports Continuous Mode with a Service Interval set to 1 ms. For
the currently defined USB speeds, this translates into a bInterval field value equal to 1 for full-speed Devices
and a bInterval field value equal to 4 for high-speed and SuperSpeed Devices. Additional Alternate Settings are
allowed to support different levels of Bursting.
4.2.3 SYNCHRONIZATION TYPE
Basic Audio Functions shall support the same Synchronization Type on all of their streaming endpoints. Only
Synchronous or Asynchronous Synchronization Types are allowed.
The implemented Synchronization Type is indicated in the bmAttributes field of the standard Endpoint
descriptor of the AudioStreaming interface.
For an Asynchronous Sink implementation, the AudioStreaming interface shall implement an Explicit Feedback
endpoint for synchronization purposes, so that the Sink endpoint can operate independently from a Source
endpoint that may be present in the same Audio Function. This allows the Host to selectively bring the input
section Power Domain of the Audio Function into a lower Power State when not in use.
4.2.4 SAMPLING FREQUENCY & BIT DEPTH
All BADD AudioStreaming interfaces shall only support 48 kHz. They shall support both 16 bits and 24 bits
sample sizes.
4.2.5 CLUSTER DESCRIPTORS
A BADD Device can only support one of two Cluster configurations.
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© USB-IF:1997-2016
4.2.5.1 MONO CLUSTER DESCRIPTOR
Table 4-1: Mono Cluster Descriptor
Offset Field Size Value Description
0 wLength 2 0x0010 Total length of the Cluster descriptor, in bytes: 16.
2 bDescriptorType 1 0x26 CS_CLUSTER descriptor type.
3 bDescriptorSubtype 1 0x00 SUBTYPE_UNDEFINED descriptor subtype.
4 wDescriptorID 2 0x0001 Unique ID of this Cluster descriptor.
6 bNrChannels 1 1 Mono Cluster.
7 wLength 2 0x0006 Length of the Information Segment, in bytes.
9 bSegmentType 1 0x20 CHANNEL_INFORMATION.
10 bChPurpose 1 0x00 Generic Audio.
11 bChRelationship 1 0x01 Mono.
12 bChGroupID 1 0x00 ID used to group channels together.
13 wLength 2 0x0003 Length of the End Segment, in bytes.
15 bSegmentType 1 0xFF END_SEGMENT.

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4.2.5.2 STEREO CLUSTER DESCRIPTOR
Table 4-2: Stereo Cluster Descriptor
Offset Field Size Value Description
0 wLength 2 0x0019 Total length of the Cluster descriptor, in bytes: 25.
2 bDescriptorType 1 0x26 CS_CLUSTER descriptor type.
3 bDescriptorSubtype 1 0x00 SUBTYPE_UNDEFINED descriptor subtype.
4 wDescriptorID 2 0x0002 Unique ID of this Cluster descriptor.
6 bNrChannels 1 2 Stereo Cluster.
7 wLength 2 0x0006 Length of the Information Segment, in bytes.
9 bSegmentType 1 0x20 CHANNEL_INFORMATION.
10 bChPurpose 1 0x00 Generic Audio.
11 bChRelationship 1 0x02 Left.
12 bChGroupID 1 0x00 ID used to group channels together.
13 wLength 2 0x0003 Length of the End Segment, in bytes.
15 bSegmentType 1 0xFF END_SEGMENT.
16 wLength 2 0x0006 Length of the Information Segment, in bytes.
18 bSegmentType 1 0x20 CHANNEL_INFORMATION.
19 bChPurpose 1 0x00 Generic Audio.
20 bChRelationship 1 0x03 Right.
21 bChGroupID 1 0x00 ID used to group channels together.
22 wLength 2 0x0003 Length of the End Segment, in bytes.
24 bSegmentType 1 0xFF END_SEGMENT.
4.3 POWER CONSIDERATIONS
Per the ADC 3.0 specification, a bus-powered Device that contains an Audio Function shall support the LPM/L1
power state. Refer to the ADC 3.0 specification for further details.
Note that the use of audio bursting and LPM/L1 enables considerable power savings.
4.3.1 POWER DOMAINS
The Output functionality of the Basic Audio Function, if present shall reside in its own independent Power
Domain. Likewise, the Input functionality, if present, shall also reside in its own independent Power Domain.
This allows the Host to selectively reduce power consumption when parts of the Basic Audio Function are
currently not being used.
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5 TOPOLOGIES
5.1 BAOF TOPOLOGY
All Basic Audio Output Functions shall use the BAOF topology (BAOFT) presented below.
Input Terminal ID1 represents the AudioStreaming Interface that is used to stream the BAOF data from the
Host to the BAOF (mono or stereo). The Output Pin of Input Terminal ID1 is connected to the Input Pin of
Feature Unit ID2. The Output Pin of Feature Unit ID2 is connected to the Input Pin of Output Terminal ID3,
which represents the physical audio output of the device.
All building blocks (Input Terminal, Feature Unit, etc.) shall be present as indicated in Figure 5-1 below and the
ID fields of the respective Entity descriptors shall be assigned as follows:
• Input Terminal ID1: bTerminalID = 1
• Feature Unit ID2: bUnitID = 2
• Output Terminal ID3: bTerminalID = 3
• Clock Source Entity ID9: bClockID = 9
• Power Domain ID10: bPowerDomainID = 10
The single Clock Source Entity ID9 provides the sampling clock for the entire BAOF. All of its timing aspects are
referenced to the Start of Bus Interval on the USB.
Input Terminal ID1 and Output Terminal ID3 belong to the single Power Domain ID10.
The audio signal path may be mono (x = 1) or stereo (x = 2). If the AudioStreaming interface suppor
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