snd-usb driver

snd-usb driver

[Lucas Takejame]

Hello guys, I'm new here. The company that i work for is developing a LV2
host pedal board (http://portalmod.com/en/index.html) and my job now is to
find if I can improve in anyway our usb driver (which is the kernel's
snd-usb driver). I know the code is already optimized but I was hoping
that, since we only use one specific sound card and we won't need a generic
driver, I could change something in the code to optimize it latency wise. I
have only a brief knowledge on the USB protocol and even less on writing
drivers, so I'm here first to ask if it's possible to improve latency by
changing the driver's code and, if possible, if you guys could give me some
directions on how to do it.

Thanks in advance,

Lucas

Re: snd-usb driver

[Clemens Ladisch]

Lucas Takejame wrote:
> I was hoping that, since we only use one specific sound card and we won't
> need a generic driver, I could change something in the code to optimize it
> latency wise.

USB packets are transferred in frames (or microframes).  The driver already
allows to use a buffer with only two frames; you cannot go below this
hardware limit.


Regards,
Clemens

Re: snd-usb driver

[Gabriel M. Beddingfield]

Hi Lucas,

I wonder if I've misunderstood what you're trying to accomplish...

On 12/11/2013 08:59 AM, Lucas Takejame wrote:
> snd-usb driver). I know the code is already optimized but I was hoping
> that, since we only use one specific sound card and we won't need a generic
> driver, I could change something in the code to optimize it latency wise. I

Are you creating a product that *is* a USB sound card and you want to 
write a driver for it?

...or do you have some pre-existing USB sound card (and driver) that 
this product is using and you're trying to set up a low-latency audio 
workstation that uses it?

-gabe

Re: snd-usb driver

[Lucas Takejame]

The product is the pedal board actually (which has the same hardware as a
computer, but with the necessary changes to work out in a gig, like a
hardcase and audio dedicated OS), we designed the sound card. I was only
wondering if there was anything that I could change considering that we
have a fixed mother board ( Intel DN2800MT ) and sound card ( works with a
TUSB3200A and AK5386 ADC, AK4382A DAC, if that helps hehe), i don't know
how much the driver being generic interfere in the performance, that is my
doubt.

Thanks for the responses,

Lucas


2013/12/12 Gabriel M. Beddingfield <gabrbedd@gmail.com>

>
> Hi Lucas,
>
> I wonder if I've misunderstood what you're trying to accomplish...
>
>
> On 12/11/2013 08:59 AM, Lucas Takejame wrote:
>
>> snd-usb driver). I know the code is already optimized but I was hoping
>> that, since we only use one specific sound card and we won't need a
>> generic
>> driver, I could change something in the code to optimize it latency wise.
>> I
>>
>
> Are you creating a product that *is* a USB sound card and you want to
> write a driver for it?
>
> ...or do you have some pre-existing USB sound card (and driver) that this
> product is using and you're trying to set up a low-latency audio
> workstation that uses it?
>
> -gabe
>
>


-- 
Lucas Conejero Takejame
Engenharia Elétrica - ênfase em computação
Escola Politécnica - USP

Re: snd-usb driver

[Patrick Shirkey]

On Fri, December 13, 2013 3:24 am, Lucas Takejame wrote:
> The product is the pedal board actually (which has the same hardware as a
> computer, but with the necessary changes to work out in a gig, like a
> hardcase and audio dedicated OS), we designed the sound card. I was only
> wondering if there was anything that I could change considering that we
> have a fixed mother board ( Intel DN2800MT ) and sound card ( works with a
> TUSB3200A and AK5386 ADC, AK4382A DAC, if that helps hehe), i don't know
> how much the driver being generic interfere in the performance, that is my
> doubt.
>

A well built standards compliant USB audio device will be able to handle
64 frames/period with the generic driver.

Have you run any benchmarks?

What is the lowest period size you can use with jack without getting
dropouts?

There may be some additional steps to configure your system for low
latency. In that case it is probably more appropriate to discuss on JACK
mailing list or back on LAD :-)


> Thanks for the responses,
>
> Lucas
>
>
> 2013/12/12 Gabriel M. Beddingfield <gabrbedd@gmail.com>
>
>>
>> Hi Lucas,
>>
>> I wonder if I've misunderstood what you're trying to accomplish...
>>
>>
>> On 12/11/2013 08:59 AM, Lucas Takejame wrote:
>>
>>> snd-usb driver). I know the code is already optimized but I was hoping
>>> that, since we only use one specific sound card and we won't need a
>>> generic
>>> driver, I could change something in the code to optimize it latency
>>> wise.
>>> I
>>>
>>
>> Are you creating a product that *is* a USB sound card and you want to
>> write a driver for it?
>>
>> ...or do you have some pre-existing USB sound card (and driver) that
>> this
>> product is using and you're trying to set up a low-latency audio
>> workstation that uses it?
>>
>> -gabe
>>
>>
>
>
> --
> Lucas Conejero Takejame
> Engenharia Elétrica - ênfase em computação
> Escola Politécnica - USP
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@alsa-project.org
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>


--
Patrick Shirkey
Boost Hardware Ltd