USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 126
Offset Field Size Value Description
5 bInterfaceClass 1 0x01 AUDIO.
6 bInterfaceSubclass 1 0x02 AUDIO_STREAMING.
7 bInterfaceProtocol 1 0x00 Unused.
8 iInterface 1 0x00 Unused.
C.3.5.2 Operational Alternate Setting 1
C.3.5.2.1.1 Standard AS Interface Descriptor
Table C-21: USB Telephone Standard AS Interface Descriptor
Offset Field Size Value Description
0 bLength 1 0x09 Size of this descriptor, in bytes.
1 bDescriptorType 1 0x04 INTERFACE descriptor.
2 bInterfaceNumber 1 0x01 Index of this interface.
3 bAlternateSetting 1 0x01 Index of this setting.
4 bNumEndpoints 1 0x01 1 endpoint.
5 bInterfaceClass 1 0x01 AUDIO.
6 bInterfaceSubclass 1 0x02 AUDIO_STREAMING.
7 bInterfaceProtocol 1 0x00 Unused.
8 iInterface 1 0x00 Unused.
C.3.5.2.1.2 Class-specific AS Interface Descriptor
Table C-22: USB Telephone Class-specific AS 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.
3 bTerminalLink 1 0x06 USB Streaming Out Terminal
4 bDelay 1 0x01 Interface delay.
5 wFormatTag 2 0x0001 PCM format.
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 127
C.3.5.2.1.3 Type I format type descriptor
Table C-23: USB Telephone 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.
2 bDescriptorSubtype 1 0x02 FORMAT_TYPE.
3 bFormatType 1 0x01 FORMAT_TYPE_I.
4 bNrChannels 1 0x01 One channel.
5 bSubFrameSize 1 0x02 Two bytes per slot.
6 bBitResolution 1 0x10 16 bits.
7 bSamFreqType 1 0x01 One sampling frequency.
8 tSamFreq 3 0x01F40 8000Hz is the sampling frequency.
C.3.5.2.1.4 Standard Endpoint descriptor
Table C-24: USB Telephone 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 0x0B Isochronous transfer type, synchronous
synchronization type.
4 wMaxPacketSize 2 0x0010 16 bytes (8 two-byte samples).
6 bInterval 1 0x01 One packet every frame.
7 bRefresh 1 0x00 Unused
8 bSynchAddress 1 0x00 Unused.
C.3.5.2.1.5 Class-specific Isochronous Audio Data Endpoint Descriptor
Table C-25: USB Telephone Class-specific Isoc. Audio Data Endpoint Descriptor
Offset Field Size Value Description
0 bLength 1 0x07 Size of this descriptor, in bytes.
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 128
Offset Field Size Value Description
1 bDescriptorType 1 0x25 CS_ENDPOINT.
2 bDescriptorSubtype 1 0x01 GENERAL.
3 bmAttributes 1 0x00 No sampling frequency control, no pitch
control.
4 bLockDelayUnits 1 0x00 Unused.
5 wLockDelay 2 0x0000 Unused.
C.3.6 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.
C.3.6.1 Manufacturer String Descriptor
Table C-26: USB Telephone Manufacturer 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 0x0054
0x0048
0x0045
0x0020
0x0043
0x004F
0x004D
0x0050
0x0041
0x004E
0x0059
“THE COMPANY”
C.3.6.2 Product String Descriptor
Table C-27: USB Telephone Product String Descriptor
Offset Field Size Value Description
0 bLength 1 0x16 Size of this descriptor, in bytes.
1 bDescriptorType 1 0x03 STRING descriptor.
2 bString 1 0x0054
0x0065
0x006C
0x0065
“Telephone”
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Offset Field Size Value Description
0x0070
0x0068
0x006F
0x006E
0x0065
C.4 Requests
C.4.1 Standard requests
All standard Requests, necessary to operate the device are supported. The next section presents the Set
Interface Request as an example.
C.4.1.1 Set interface
This request selects the alternate setting on interface 1 or 2 to control bandwidth allocation.
Table 5-28: Set Interface Request Values
Offset Field Size Value Description
0 bmRequestType 1 0x01 D7: 0 = Host to Device.
D6..5: 00 = Standard Request.
D4..0: 00001 = Recipient is interface.
1 bRequest 1 0x0B SET_INTERFACE.
2 wValue 2 0x0000
or
0x0001
0x00 is zero bandwidth alternate setting.
0x01 is normal isochronous operation.
4 wIndex 2 0x0001
or
0x0002
Interface number of one of the
AudioStreaming interfaces.
6 wLength 2 0x0000 No Parameter Block
C.4.2 Class-specific Requests
The only class-specific Request supported is the Set/Get Selector Control Request. The following sections
describe these requests in detail.
C.4.2.1 Set Selector Unit Control Request
This Request sets the Selector Unit Control to the desired value.
Table C-29: Set Selector Unit Control Request Values
Offset Field Size Value Description
0 bmRequestType 1 0x21 D7: 0 = Host to Device.
D6..5: 01 = Class Request.
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 130
Offset Field Size Value Description
D4..0: 00001 = Recipient is interface.
1 bRequest 1 0x01 SET_CUR.
2 wValue 2 0x0000 Must be zero.
4 wIndex 2 0x0000 Interface number of the AudioControl
interface.
6 wLength 2 0x0001 Parameter Block Length
The one-byte Parameter Block contains the new bSelector value for the Selector Control. Since all the
Selector Units have two Input Pins, the valid range for bSelector is [1,2].
C.4.2.2 Get Selector Unit Control Request
This Request retrieves the Selector Unit Control parameter.
Table C-30: Get Selector Unit Control Request Values
Offset Field Size Value Description
0 bmRequestType 1 0xA1 D7: 1 = Device to Host.
D6..5: 01 = Class Request.
D4..0: 00001 = Recipient is interface.
1 bRequest 1 0x81
0x82
0x83
0x84
GET_CUR.
GET_MIN.
GET_MAX.
GET_RES.
2 wValue 2 0x0000 Must be zero.
4 wIndex 2 0x0000 Interface number of the AudioControl
interface.
6 wLength 2 0x0001 Parameter Block Length
The actual setting of the Selector Control is returned in the one-byte Parameter Block. Since all the
Selector Units have two Input Pins, the valid range for the returned value is [1,2].
最終更新：2011年05月02日 03:26
