USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 111
Offset Field Size Value Description
6 bInterfaceSubclass 1 0x02 AUDIO_STREAMING.
7 bInterfaceProtocol 1 0x00 Unused.
8 iInterface 1 0x00 Unused.
B.3.4.2.1.2 Class-specific AS General Interface Descriptor
Table B-9: USB Microphone Class-specific AS General Interface Descriptor
Offset Field Size Value Description
0 bLength 1 0x07 Size of this descriptor, in bytes.
1 bDescriptorType 1 0x24 CS_INTERFACE descriptor.
2 bDescriptorSubtype 1 0x01 GENERAL subtype.
3 bTerminalLink 1 0x02 Unit ID of the Output Terminal.
4 bDelay 1 0x01 Interface delay.
5 wFormatTag 2 0x0001 PCM Format.
B.3.4.2.1.3 Type I Format Type Descriptor
Table B-10: USB Microphone Type I Format Type Descriptor
Offset Field Size Value Description
0 bLength 1 0x0B Size of this descriptor, in bytes.
1 bDescriptorType 1 0x24 CS_INTERFACE descriptor.
2 bDescriptorSubtype 1 0x02 FORMAT_TYPE subtype.
3 bFormatType 1 0x01 FORMAT_TYPE_I.
4 bNrChannels 1 0x01 One channel.
5 bSubFrameSize 1 0x02 Two bytes per audio subframe.
6 bBitResolution 1 0x10 16 bits per sample.
7 bSamFreqType 1 0x01 One frequency supported.
8 tSamFreq 3 0x01F40 8000Hz.
B.3.4.2.1.4 Standard Endpoint Descriptor
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Table B-11: USB Microphone Standard Endpoint Descriptor
Offset Field Size Value Description
0 bLength 1 0x09 Size of this descriptor, in bytes.
1 bDescriptorType 1 0x05 ENDPOINT descriptor.
2 bEndpointAddress 1 0x81 IN Endpoint 1.
3 bmAttributes 1 0x01 Isochronous, not shared.
4 wMaxPacketSize 2 0x0010 16 bytes per packet.
6 bInterval 1 0x01 One packet per frame.
7 bRefresh 1 0x00 Unused.
8 bSynchAddress 1 0x00 Unused.
B.3.4.2.1.5 Class-specific Isochronous Audio Data Endpoint Descriptor
Table B-12: USB Microphone Class-specific Isoc. Audio Data Endpoint Descriptor
Offset Field Size Value Description
0 bLength 1 0x07 Size of this descriptor, in bytes.
1 bDescriptorType 1 0x25 CS_ENDPOINT descriptor
2 bDescriptorSubtype 1 0x01 GENERAL subtype.
3 bmAttributes 1 0x00 No sampling frequency control, no pitch
control, no packet padding.
4 bLockDelayUnits 1 0x00 Unused.
5 wLockDelay 2 0x0000 Unused.
B.3.5 String Descriptors
There are two string descriptors available. The first string descriptor contains the Manufacturer
information and the second one contains Product related information. The following sections present an
example of how these descriptors could look like.
B.3.5.1 Manufacturer String Descriptor
Table B-13: USB Microphone Manufacturer String Descriptor
Offset Field Size Value Description
0 bLength 1 0x18 Size of this descriptor, in bytes.
1 bDescriptorType 1 0x03 STRING descriptor.
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Offset Field Size Value Description
2 bString 1 0x0054
0x0048
0x0045
0x0020
0x0043
0x004F
0x004D
0x0050
0x0041
0x004E
0x0059
“THE COMPANY”
B.3.5.2 Product String Descriptor
Table B-14: USB Microphone Product String Descriptor
Offset Field Size Value Description
0 bLength 1 0x18 Size of this descriptor, in bytes.
1 bDescriptorType 1 0x03 STRING descriptor.
2 bString 1 0x004D
0x0069
0x0063
0x0072
0x006F
0x0070
0x0068
0x006F
0x006E
0x0065
“Microphone”
B.4 Requests
B.4.1 Standard Requests
The microphone supports all necessary standard requests.
B.4.2 Class-specific Requests
There are no class-specific requests supported.
USB Device Class Definition for Audio Devices
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Appendix C. Example 2: USB Telephone (Informative)
C.1 Product Description
This is a USB Telephone with 16-bit 8KHz input and output. It has a handset and Phone line in and out
connectors. Selector Units are used to allow the Host to talk directly to the telephone line or to allow the
handset to be used with the Host for an Internet telephone call. This is an analog device. The telephone
line and handset signals are analog and all switching is performed in the analog domain. The digital USB
audio stream, coming from AudioStreaming interface 1 is converted to the analog domain before entering
the audio function through Input Terminal ID3. Likewise, the analog signal coming from Selector Unit
ID9 is delivered to Output Terminal ID6 and converted back to the digital domain before it is delivered to
AudioStreaming interface 2.
AudioStreaming
Interface #2
Audio Function
Phone Line IT OT
USB IN Endpoint
IT
IT
OT
OT
Phone Line
Handset Handset
ID1
ID2
ID3 ID9
ID7
ID8
ID4
ID5
ID6
AudioStreaming
Interface #1
USB OUT Endpoint
Figure C-1: USB Telephone Topology
It is a neat device, but telephones that are much more elaborate could be constructed with speakerphone
and acoustic echo cancellation incorporated.
C.2 Descriptor Hierarchy
This USB Telephone device includes an AudioControl interface (0) and two AudioStreaming interfaces
(1&2). The AudioStreaming interfaces both feature two alternate settings. The first alternate setting
(Alternate Setting 0) has zero bandwidth associated with it so that switching to this alternate setting
effectively frees all allocated bandwidth on the USB for this device. Zero bandwidth is indicated by the
lack of a streaming endpoint. Alternate Setting 1 is the operational part of the interface and it has one
isochronous endpoint. Figure presents the descriptor hierarchy.
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 115
Interface 0
Device
Configuration
AudioControl I/F
Header
Phone Line IT
Handset IT
Standard Descriptors
Class-Specific
Descriptors
USB OUT EP IT
Phone Line OT
Handset OT
USB IN EP OT
Phone Line SU
Handset SU
USB OUT SU
AS I/F Alt. Setting 0 Interface 1
AS I/F Alt. Setting 1
General
Type I Format
Endpoint
Endpoint
ID1
ID2
ID3
ID4
ID5
ID6
ID7
ID8
ID9
AS I/F Alt. Setting 0 Interface 2
AS I/F Alt. Setting 1
General
Type I Format
Endpoint
Endpoint
Figure C-2: USB Telephone Descriptor Hierarchy
C.3 Descriptors
The following sections present all the descriptors that are used to describe the device.
C.3.1 Device Descriptor
Table C-1: USB Telephone Device Descriptor
Offset Field Size Value Description
0 bLength 1 0x12 Size of this descriptor, in bytes.
1 bDescriptorType 1 0x01 DEVICE descriptor.
2 bcdUSB 2 0x0100 1.00 - current revision of USB spec.
4 bDeviceClass 1 0x00 Device defined at Interface level.
最終更新：2011年05月02日 03:35
