On 01/09/17 12:34 AM, Takashi Iwai wrote:
On Wed, 30 Aug 2017 21:48:58 +0200,
Jack Bates wrote:
I confirmed with Wireshark that my USB sound card responds to GET_MIN
with 0x0000 and GET_MAX with 0x6300 .. The audio device class
definition [1] says the units are 1/256 dB (section 5.2.2.2.3: Mixer
Control) ... So by my calculation, the min and max are 0 and 99 dB
(0x6300 / 256 == 99) ... Why then does alsactl print:
range '0 - 99'
dbmin 0
dbmax 38
(/usr/sbin/aslactl -f - store)
I originally asked about this on the pulseaudio-discuss list [2]
because it uses "dB data" [3].
The "0 - 99" makes sense -- it lines up with my calculation ... Where
does the 38 come from? (I expect it's obvious, I just haven't found
the explanation?)
Hm, what shows /proc/asound/card*/usbmixer proc file?
It contains some raw data.
It also shows dBmax=38 (it matches alsactl):
nottheoilrig@debian:~$ cat /proc/asound/card2/usbmixer
USB Mixer: usb_id=0x05a740fa, ctrlif=0, ctlerr=0
Card: Bose Corporation Bose Revolve SoundLink at usb-0000:00:14.0-1, full speed
Unit: 2
Control: name="PCM Playback Volume", index=0
Info: id=2, control=2, cmask=0x0, channels=1, type="S16"
Volume: min=0, max=99, dBmin=0, dBmax=38
Unit: 2
Control: name="PCM Playback Switch", index=0
Info: id=2, control=1, cmask=0x0, channels=1, type="INV_BOOLEAN"
Volume: min=0, max=1, dBmin=0, dBmax=0
nottheoilrig@debian:~$
Basically the driver simply interprets the USB descriptor min/max
unless there are overriding mappings by quirk list.
How can I inspect the device's USB descriptor min/max (to confirm that
38 *is* what's advertised)? I was using Wireshark to capture the GET_MAX
request and response ([1] section 5.2.2.2.2: Get Mixer Unit Control
Request) -- in which case the response data is 0x6300 ...
If the source behind the usbmixer proc file/dB data is the GET_MAX
response, then how does 0x6300 turn into 38 dB? I haven't spotted any
obvious quirks for usb_id=0x05a740fa (although I haven't read all of
mixer.c) ... get_min_max_with_quirks() would seem to interpret it as
1/256 dB [2] (as per the spec) but 0x6300 / 256 != 38 ...
[1] http://www.usb.org/developers/docs/devclass_docs/audio10.pdf
[2]
https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/tree/sound/usb/mixer.c#n1046
Here's the lsusb output:
Bus 001 Device 008: ID 05a7:40fa Bose Corp.
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 239 Miscellaneous Device
bDeviceSubClass 2 ?
bDeviceProtocol 1 Interface Association
bMaxPacketSize0 64
idVendor 0x05a7 Bose Corp.
idProduct 0x40fa
bcdDevice 1.00
iManufacturer 1
iProduct 2
iSerial 3
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 156
bNumInterfaces 3
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xc0
Self Powered
MaxPower 500mA
Interface Association:
bLength 8
bDescriptorType 11
bFirstInterface 0
bInterfaceCount 2
bFunctionClass 1 Audio
bFunctionSubClass 1 Control Device
bFunctionProtocol 0
iFunction 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 1 Control Device
bInterfaceProtocol 0
iInterface 0
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 1.00
wTotalLength 43
bInCollection 1
baInterfaceNr( 0) 1
AudioControl Interface Descriptor:
bLength 12
bDescriptorType 36
bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 1
wTerminalType 0x0101 USB Streaming
bAssocTerminal 0
bNrChannels 2
wChannelConfig 0x0003
Left Front (L)
Right Front (R)
iChannelNames 0
iTerminal 0
AudioControl Interface Descriptor:
bLength 13
bDescriptorType 36
bDescriptorSubtype 6 (FEATURE_UNIT)
bUnitID 2
bSourceID 1
bControlSize 2
bmaControls( 0) 0x03
bmaControls( 0) 0x00
Mute Control
Volume Control
bmaControls( 1) 0x00
bmaControls( 1) 0x00
bmaControls( 2) 0x00
bmaControls( 2) 0x00
iFeature 0
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 3
wTerminalType 0x0301 Speaker
bAssocTerminal 0
bSourceID 2
iTerminal 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 0
iInterface 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 1
bNumEndpoints 1
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 0
iInterface 0
AudioStreaming Interface Descriptor:
bLength 7
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 1
bDelay 0 frames
wFormatTag 1 PCM
AudioStreaming Interface Descriptor:
bLength 14
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bNrChannels 2
bSubframeSize 2
bBitResolution 16
bSamFreqType 2 Discrete
tSamFreq[ 0] 48000
tSamFreq[ 1] 44100
AudioControl Endpoint Descriptor:
bLength 7
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x81
Sampling Frequency
MaxPacketsOnly
bLockDelayUnits 0 Undefined
wLockDelay 0 Undefined
Endpoint Descriptor:
bLength 9
bDescriptorType 5
bEndpointAddress 0x03 EP 3 OUT
bmAttributes 1
Transfer Type Isochronous
Synch Type None
Usage Type Data
wMaxPacketSize 0x00c0 1x 192 bytes
bInterval 1
bRefresh 0
bSynchAddress 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 3 Human Interface Device
bInterfaceSubClass 0 No Subclass
bInterfaceProtocol 0 None
iInterface 0
HID Device Descriptor:
bLength 9
bDescriptorType 33
bcdHID 1.11
bCountryCode 0 Not supported
bNumDescriptors 1
bDescriptorType 34 Report
wDescriptorLength 126
Report Descriptors:
** UNAVAILABLE **
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 1
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x02 EP 2 OUT
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 1
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