I am trying to understand USB descriptors. For exploration I acquired my USB headphone descriptor using usbtreeview software. My understanding of descriptor hierarchy is:
---------------------- Device Descriptor ----------------------
bLength : 0x12 (18 bytes)
bDescriptorType : 0x01 (Device Descriptor)
bcdUSB : 0x200 (USB Version 2.0) -> but device is Full-Speed only
bDeviceClass : 0x00 (defined by the interface descriptors)
bDeviceSubClass : 0x00
bDeviceProtocol : 0x00
bMaxPacketSize0 : 0x40 (64 bytes)
idVendor : 0x046D (Logitech Inc.)
idProduct : 0x0A38
bcdDevice : 0x0117
iManufacturer : 0x01 (String Descriptor 1)
Language 0x0409 : "Logitech Inc."
iProduct : 0x02 (String Descriptor 2)
Language 0x0409 : "Logi USB Headset H340"
iSerialNumber : 0x00 (No String Descriptor)
bNumConfigurations : 0x01 (1 Configuration)
Data (HexDump) : 12 01 00 02 00 00 00 40 6D 04 38 0A 17 01 01 02 .......@m.8.....
00 01 ..
------------------ Configuration Descriptor -------------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x02 (Configuration Descriptor)
wTotalLength : 0x00EB (235 bytes)
bNumInterfaces : 0x04 (4 Interfaces)
bConfigurationValue : 0x01 (Configuration 1)
iConfiguration : 0x00 (No String Descriptor)
bmAttributes : 0x80
D7: Reserved, set 1 : 0x01
D6: Self Powered : 0x00 (no)
D5: Remote Wakeup : 0x00 (no)
D4..0: Reserved, set 0 : 0x00
MaxPower : 0x3C (120 mA)
Data (HexDump) : 09 02 EB 00 04 01 00 80 3C 09 04 00 00 00 01 01 ........<.......
00 00 0A 24 01 00 01 4F 00 02 01 02 0C 24 02 02 ...$...O.....$..
01 01 00 02 03 00 00 00 0C 24 02 01 01 02 00 02 .........$......
03 00 00 00 09 24 03 03 01 01 00 0A 00 09 24 03 .....$........$.
04 01 03 00 05 00 0A 24 06 05 02 01 01 02 02 00 .......$........
0A 24 06 06 01 01 03 00 00 00 07 24 05 0A 01 06 .$.........$....
00 09 04 01 00 00 01 02 00 00 09 04 01 01 02 01 ................
02 00 00 07 24 01 02 01 01 00 0B 24 02 01 02 02 ....$......$....
10 01 44 AC 00 09 05 01 05 C8 00 01 00 83 07 25 ..D............%
01 00 00 00 00 09 05 83 01 03 00 01 05 00 09 04 ................
02 00 00 01 02 00 00 09 04 02 01 01 01 02 00 00 ................
07 24 01 03 01 01 00 0B 24 02 01 02 02 10 01 44 .$......$......D
AC 00 09 05 81 05 C8 00 01 00 00 07 25 01 00 00 ............%...
00 00 09 04 03 00 01 03 00 00 00 09 21 11 01 00 ............!...
01 22 6F 00 07 05 84 03 04 00 0A ."o........
---------------- Interface Descriptor -----------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x04 (Interface Descriptor)
bInterfaceNumber : 0x00 (Interface 0)
bAlternateSetting : 0x00
bNumEndpoints : 0x00 (Default Control Pipe only)
bInterfaceClass : 0x01 (Audio)
bInterfaceSubClass : 0x01 (Audio Control)
bInterfaceProtocol : 0x00
iInterface : 0x00 (No String Descriptor)
Data (HexDump) : 09 04 00 00 00 01 01 00 00 .........
------ Audio Control Interface Header Descriptor ------
bLength : 0x0A (10 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x01 (Header)
bcdADC : 0x0100
wTotalLength : 0x004F (79 bytes)
bInCollection : 0x02
baInterfaceNr[1] : 0x01
baInterfaceNr[2] : 0x02
Data (HexDump) : 0A 24 01 00 01 4F 00 02 01 02 .$...O....
------- Audio Control Input Terminal Descriptor -------
bLength : 0x0C (12 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x02 (Input Terminal)
bTerminalID : 0x02
wTerminalType : 0x0101 (USB Streaming)
bAssocTerminal : 0x00
bNrChannels : 0x02 (2 channels)
wChannelConfig : 0x0003 (L, R)
iChannelNames : 0x00 (No String Descriptor)
iTerminal : 0x00 (No String Descriptor)
Data (HexDump) : 0C 24 02 02 01 01 00 02 03 00 00 00 .$..........
------- Audio Control Input Terminal Descriptor -------
bLength : 0x0C (12 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x02 (Input Terminal)
bTerminalID : 0x01
wTerminalType : 0x0201 (Microphone)
bAssocTerminal : 0x00
bNrChannels : 0x02 (2 channels)
wChannelConfig : 0x0003 (L, R)
iChannelNames : 0x00 (No String Descriptor)
iTerminal : 0x00 (No String Descriptor)
Data (HexDump) : 0C 24 02 01 01 02 00 02 03 00 00 00 .$..........
------- Audio Control Output Terminal Descriptor ------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x03 (Output Terminal)
bTerminalID : 0x03
wTerminalType : 0x0101 (USB Streaming)
bAssocTerminal : 0x00 (0)
bSourceID : 0x0A (10)
iTerminal : 0x00 (No String Descriptor)
Data (HexDump) : 09 24 03 03 01 01 00 0A 00 .$.......
------- Audio Control Output Terminal Descriptor ------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x03 (Output Terminal)
bTerminalID : 0x04
wTerminalType : 0x0301 (Speaker)
bAssocTerminal : 0x00 (0)
bSourceID : 0x05 (5)
iTerminal : 0x00 (No String Descriptor)
Data (HexDump) : 09 24 03 04 01 03 00 05 00 .$.......
-------- Audio Control Feature Unit Descriptor --------
bLength : 0x0A (10 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x06 (Feature Unit)
bUnitID : 0x05 (5)
bSourceID : 0x02 (2)
bControlSize : 0x01 (1 byte per control)
bmaControls[0] : 0x01
D0: Mute : 1
D1: Volume : 0
D2: Bass : 0
D3: Mid : 0
D4: Treble : 0
D5: Graphic Equalizer : 0
D6: Automatic Gain : 0
D7: Delay : 0
bmaControls[1] : 0x02
D0: Mute : 0
D1: Volume : 1
D2: Bass : 0
D3: Mid : 0
D4: Treble : 0
D5: Graphic Equalizer : 0
D6: Automatic Gain : 0
D7: Delay : 0
bmaControls[2] : 0x02
D0: Mute : 0
D1: Volume : 1
D2: Bass : 0
D3: Mid : 0
D4: Treble : 0
D5: Graphic Equalizer : 0
D6: Automatic Gain : 0
D7: Delay : 0
iFeature : 0x00 (No String Descriptor)
Data (HexDump) : 0A 24 06 05 02 01 01 02 02 00 .$........
-------- Audio Control Feature Unit Descriptor --------
bLength : 0x0A (10 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x06 (Feature Unit)
bUnitID : 0x06 (6)
bSourceID : 0x01 (1)
bControlSize : 0x01 (1 byte per control)
bmaControls[0] : 0x03
D0: Mute : 1
D1: Volume : 1
D2: Bass : 0
D3: Mid : 0
D4: Treble : 0
D5: Graphic Equalizer : 0
D6: Automatic Gain : 0
D7: Delay : 0
bmaControls[1] : 0x00
D0: Mute : 0
D1: Volume : 0
D2: Bass : 0
D3: Mid : 0
D4: Treble : 0
D5: Graphic Equalizer : 0
D6: Automatic Gain : 0
D7: Delay : 0
bmaControls[2] : 0x00
D0: Mute : 0
D1: Volume : 0
D2: Bass : 0
D3: Mid : 0
D4: Treble : 0
D5: Graphic Equalizer : 0
D6: Automatic Gain : 0
D7: Delay : 0
iFeature : 0x00 (No String Descriptor)
Data (HexDump) : 0A 24 06 06 01 01 03 00 00 00 .$........
------- Audio Control Selector Unit Descriptor --------
bLength : 0x07 (7 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x05 (Selector Unit)
bUnitID : 0x0A
bNrInPins : 0x01 (1 Input Pin)
baSourceID[1] : 0x06 (6)
iSelector : 0x00 (No String Descriptor)
Data (HexDump) : 07 24 05 0A 01 06 00 .$.....
---------------- Interface Descriptor -----------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x04 (Interface Descriptor)
bInterfaceNumber : 0x01 (Interface 1)
bAlternateSetting : 0x00
bNumEndpoints : 0x00 (Default Control Pipe only)
bInterfaceClass : 0x01 (Audio)
bInterfaceSubClass : 0x02 (Audio Streaming)
bInterfaceProtocol : 0x00
iInterface : 0x00 (No String Descriptor)
Data (HexDump) : 09 04 01 00 00 01 02 00 00 .........
---------------- Interface Descriptor -----------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x04 (Interface Descriptor)
bInterfaceNumber : 0x01 (Interface 1)
bAlternateSetting : 0x01
bNumEndpoints : 0x02 (2 Endpoints)
bInterfaceClass : 0x01 (Audio)
bInterfaceSubClass : 0x02 (Audio Streaming)
bInterfaceProtocol : 0x00
iInterface : 0x00 (No String Descriptor)
Data (HexDump) : 09 04 01 01 02 01 02 00 00 .........
-------- Audio Streaming Interface Descriptor ---------
bLength : 0x07 (7 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x01 (AS_GENERAL)
bTerminalLink : 0x02 (Terminal ID 2)
bDelay : 0x01 (1 frame)
wFormatTag : 0x0001 (PCM)
Data (HexDump) : 07 24 01 02 01 01 00 .$.....
------- Audio Streaming Format Type Descriptor --------
bLength : 0x0B (11 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x02 (Format Type)
bFormatType : 0x01 (FORMAT_TYPE_I)
bNrChannels : 0x02 (2 channels)
bSubframeSize : 0x02 (2 bytes per subframe)
bBitResolution : 0x10 (16 bits per sample)
bSamFreqType : 0x01 (supports 1 sample frequence)
tSamFreq[1] : 0x0AC44 (44100 Hz)
Data (HexDump) : 0B 24 02 01 02 02 10 01 44 AC 00 .$......D..
----------------- Endpoint Descriptor -----------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x05 (Endpoint Descriptor)
bEndpointAddress : 0x01 (Direction=OUT EndpointID=1)
bmAttributes : 0x05 (TransferType=Isochronous SyncType=Asynchronous EndpointType=Data)
wMaxPacketSize : 0x00C8 (200 bytes)
bInterval : 0x01 (1 ms)
bRefresh : 0x00
bSynchAddress : 0x83 (Direction=IN EndpointID=3)
Data (HexDump) : 09 05 01 05 C8 00 01 00 83 .........
----------- Audio Data Endpoint Descriptor ------------
bLength : 0x07 (7 bytes)
bDescriptorType : 0x25 (Audio Endpoint Descriptor)
bDescriptorSubtype : 0x01 (General)
bmAttributes : 0x00
D0 : Sampling Freq : 0x00 (not supported)
D1 : Pitch : 0x00 (not supported)
D6..2: Reserved : 0x00
D7 : MaxPacketsOnly : 0x00 (no)
bLockDelayUnits : 0x00 (Undefined)
wLockDelay : 0x0000
Data (HexDump) : 07 25 01 00 00 00 00 .%.....
----------------- Endpoint Descriptor -----------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x05 (Endpoint Descriptor)
bEndpointAddress : 0x83 (Direction=IN EndpointID=3)
bmAttributes : 0x01 (TransferType=Isochronous SyncType=None EndpointType=Data)
wMaxPacketSize : 0x0003 (3 bytes)
bInterval : 0x01 (1 ms)
bRefresh : 0x05 (32 ms)
bSynchAddress : 0x00
Data (HexDump) : 09 05 83 01 03 00 01 05 00 .........
---------------- Interface Descriptor -----------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x04 (Interface Descriptor)
bInterfaceNumber : 0x02 (Interface 2)
bAlternateSetting : 0x00
bNumEndpoints : 0x00 (Default Control Pipe only)
bInterfaceClass : 0x01 (Audio)
bInterfaceSubClass : 0x02 (Audio Streaming)
bInterfaceProtocol : 0x00
iInterface : 0x00 (No String Descriptor)
Data (HexDump) : 09 04 02 00 00 01 02 00 00 .........
---------------- Interface Descriptor -----------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x04 (Interface Descriptor)
bInterfaceNumber : 0x02 (Interface 2)
bAlternateSetting : 0x01
bNumEndpoints : 0x01 (1 Endpoint)
bInterfaceClass : 0x01 (Audio)
bInterfaceSubClass : 0x02 (Audio Streaming)
bInterfaceProtocol : 0x00
iInterface : 0x00 (No String Descriptor)
Data (HexDump) : 09 04 02 01 01 01 02 00 00 .........
-------- Audio Streaming Interface Descriptor ---------
bLength : 0x07 (7 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x01 (AS_GENERAL)
bTerminalLink : 0x03 (Terminal ID 3)
bDelay : 0x01 (1 frame)
wFormatTag : 0x0001 (PCM)
Data (HexDump) : 07 24 01 03 01 01 00 .$.....
------- Audio Streaming Format Type Descriptor --------
bLength : 0x0B (11 bytes)
bDescriptorType : 0x24 (Audio Interface Descriptor)
bDescriptorSubtype : 0x02 (Format Type)
bFormatType : 0x01 (FORMAT_TYPE_I)
bNrChannels : 0x02 (2 channels)
bSubframeSize : 0x02 (2 bytes per subframe)
bBitResolution : 0x10 (16 bits per sample)
bSamFreqType : 0x01 (supports 1 sample frequence)
tSamFreq[1] : 0x0AC44 (44100 Hz)
Data (HexDump) : 0B 24 02 01 02 02 10 01 44 AC 00 .$......D..
----------------- Endpoint Descriptor -----------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x05 (Endpoint Descriptor)
bEndpointAddress : 0x81 (Direction=IN EndpointID=1)
bmAttributes : 0x05 (TransferType=Isochronous SyncType=Asynchronous EndpointType=Data)
wMaxPacketSize : 0x00C8 (200 bytes)
bInterval : 0x01 (1 ms)
bRefresh : 0x00
bSynchAddress : 0x00
Data (HexDump) : 09 05 81 05 C8 00 01 00 00 .........
----------- Audio Data Endpoint Descriptor ------------
bLength : 0x07 (7 bytes)
bDescriptorType : 0x25 (Audio Endpoint Descriptor)
bDescriptorSubtype : 0x01 (General)
bmAttributes : 0x00
D0 : Sampling Freq : 0x00 (not supported)
D1 : Pitch : 0x00 (not supported)
D6..2: Reserved : 0x00
D7 : MaxPacketsOnly : 0x00 (no)
bLockDelayUnits : 0x00 (Undefined)
wLockDelay : 0x0000
Data (HexDump) : 07 25 01 00 00 00 00 .%.....
---------------- Interface Descriptor -----------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x04 (Interface Descriptor)
bInterfaceNumber : 0x03 (Interface 3)
bAlternateSetting : 0x00
bNumEndpoints : 0x01 (1 Endpoint)
bInterfaceClass : 0x03 (HID - Human Interface Device)
bInterfaceSubClass : 0x00 (None)
bInterfaceProtocol : 0x00 (None)
iInterface : 0x00 (No String Descriptor)
Data (HexDump) : 09 04 03 00 01 03 00 00 00 .........
------------------- HID Descriptor --------------------
bLength : 0x09 (9 bytes)
bDescriptorType : 0x21 (HID Descriptor)
bcdHID : 0x0111 (HID Version 1.11)
bCountryCode : 0x00 (00 = not localized)
bNumDescriptors : 0x01
Data (HexDump) : 09 21 11 01 00 01 22 6F 00 .!...."o.
Descriptor 1:
bDescriptorType : 0x22 (Class=Report)
wDescriptorLength : 0x006F (111 bytes)
Error reading descriptor : ERROR_INVALID_PARAMETER (due to a obscure limitation of the Win32 USB API, see UsbTreeView.txt)
----------------- Endpoint Descriptor -----------------
bLength : 0x07 (7 bytes)
bDescriptorType : 0x05 (Endpoint Descriptor)
bEndpointAddress : 0x84 (Direction=IN EndpointID=4)
bmAttributes : 0x03 (TransferType=Interrupt)
wMaxPacketSize : 0x0004 (4 bytes)
bInterval : 0x0A (10 ms)
Data (HexDump) : 07 05 84 03 04 00 0A .......
----------------- Device Qualifier Descriptor -----------------
Error : ERROR_GEN_FAILURE (because the device is Full-Speed only)
-------------------- String Descriptors -------------------
------ String Descriptor 0 ------
bLength : 0x04 (4 bytes)
bDescriptorType : 0x03 (String Descriptor)
Language ID[0] : 0x0409 (English - United States)
Data (HexDump) : 04 03 09 04 ....
------ String Descriptor 1 ------
bLength : 0x1C (28 bytes)
bDescriptorType : 0x03 (String Descriptor)
Language 0x0409 : "Logitech Inc."
Data (HexDump) : 1C 03 4C 00 6F 00 67 00 69 00 74 00 65 00 63 00 ..L.o.g.i.t.e.c.
68 00 20 00 49 00 6E 00 63 00 2E 00 h. .I.n.c...
------ String Descriptor 2 ------
bLength : 0x2C (44 bytes)
bDescriptorType : 0x03 (String Descriptor)
Language 0x0409 : "Logi USB Headset H340"
Data (HexDump) : 2C 03 4C 00 6F 00 67 00 69 00 20 00 55 00 53 00 ,.L.o.g.i. .U.S.
42 00 20 00 48 00 65 00 61 00 64 00 73 00 65 00 B. .H.e.a.d.s.e.
74 00 20 00 48 00 33 00 34 00 30 00 t. .H.3.4.0.
My Question from attached descriptor logs:
I see only one device descriptor - All good
I see only one configuration which match entry in device descriptor. bNumConfigurations : 0x01 (1 Configuration) - All good
In the configuration descriptor I see number of interfaces equal to 4. bNumInterfaces : 0x04 (4 Interfaces) - This is where the problem starts. After this I see more than 4 interface descriptors e.g.
---------------- Interface Descriptor -----------------
------ Audio Control Interface Header Descriptor ------
------- Audio Control Input Terminal Descriptor -------
------- Audio Control Selector Unit Descriptor --------
. . . .
And So on
How the number of interface descriptors can be more than 4?
Interface descriptor a is technical term that refers to a very specific piece of data. This data starts with the bytes 0x09 (length) and 0x04 (the code for "interface descriptor").
Note that things like the "Audio Control Interface Header Descriptor" are not interface descriptors because they do not start with 0x09 0x04. They are just pieces of data that describe the interface and they go near the interface descriptors.
Your dump shows that you have six interface descriptors:
Since they each describe a different interface or a different alternate setting of an interface, I think it's fine.