[LAU] Sound Devices USBPre2, UAC2 status

[Hans Wilmers]

On 01/07/2013 08:25 PM, shal at free.fr wrote:
>
> ----- Mail original -----
>> De: "alexander" <axeldenstore at gmail.com>
>> À: linux-audio-user at lists.linuxaudio.org
>> Envoyé: Lundi 7 Janvier 2013 18:27:42
>> Objet: Re: [LAU] Sound Devices USBPre2, UAC2 status
>> I also own this interface, recently it has started to work in uac2
>> mode,
>> I still cant raise the samplerate, but it runs.. however, It still
>> runs
>> alot better in uac1.. when in uac2 jack mysteriously shuts down for
>> no
>> appearant reason. I run archlinux, allways uptodated with vanilla
>> kernel.
>>
>> This is when I connect it without pressing 1. eg, uac2
>> http://pastebin.com/BFJTwXnJ
>> And as with pressing 1. http://pastebin.com/ZJ1jbPUK
>
>
> Hi,
>
> In my understanding, you are not in UAC2 , you are in high-speed mode but the usb audio protocol remains UAC1.
>
>
> In the kernel source in the file include/uapi/linux/usb/audio.h is defined two values:
> /* bInterfaceProtocol values to denote the version of the standard used */
> #define UAC_VERSION_1			0x00
> #define UAC_VERSION_2			0x20
>
> So if the card is in UAC2 , you should see bInterfaceProtocol at 32 (or 0x20)
> By example, now the RME babyface is recognize as UAC2 device, you can view its "lsub -v" here  : http://minilien.fr/a0m3kc
>
> But for the usbPre2 device with ou without pressing the "1" button,  we have bInterfaceProtocol = 0. So we stays in UAC1, even the speed increase to high-speed.
>

I was also surprised to see that the USBPre2 now works duplex without 
pressing the "1" button while connecting.

This was tested on Fedora 17 with stock kernel 3.6.6-1.fc17.
Jack was set to 512 Frames/period and 3 periods/buffer, and in a 24h 
recording I got no xruns.
I did not manage to choose a sample rate unlike 48000, though.

With lsusb, I can see 2 configurations for the same device, and the 
second one has bInterfaceProtocol = 32 for all interfaces except HID:
http://pastebin.com/zwq0VVbM


/ Hans