Re: usb:gadget:f_uac2: EP OUT is adaptive instead of async

[Pavel Hofman <pavel.hofman@ivitera.com>]

Dne 11. 02. 20 v 20:02 Pavel Hofman napsal(a):
> Hi Ruslan,
> 
> Dne 11. 02. 20 v 17:10 Ruslan Bilovol napsal(a):
>> On Thu, Feb 6, 2020 at 3:35 PM Pavel Hofman <pavel.hofman@ivitera.com> wrote:
>>>
>>> .
>>
>> Are you working on async feedback EP implementation? I'm interested in that
>> feature and I can implement it soon but do not want to do double work
>> if somebody
>> is already working on it and will send to the community soon
> 
> I would be happy if you focused on the feedback. I want to solve the
> g_audio usability somehow first
> https://lore.kernel.org/linux-usb/df2eeff0-ca9c-35f9-2e72-8426b2cf72c9@ivitera.com/
> as it would allow easy usage of the existing adaptive gadget version.
> 
> The feedback - I have been shown a simple implementation which is not
> public and is not using the g_audio alsa device on the other side.
> 
> IMO the key issue is designing the async feedback to accept feedback
> values from userspace as well as from any third-party kernel module. Why
> userspace? The stream provided by the g_audio capture device  can be
> output to a real master-clock alsa device (e.g. after synchronous
> resampling), be sent by network to some master-clock device, many other
> options possible. Any master-clock output device/ userspace sink should
> be able to provide data for calculating proper up-to-date feedback value
> for the slaved UAC2 gadget.
> 
> I have done a few trials with master alsa output device -
> 
> https://www.diyaudio.com/forums/pc-based/342070-linux-usb-audio-gadget-rpi4-otg.html#post5909816
> 
> 
> https://www.diyaudio.com/forums/pc-based/342070-linux-usb-audio-gadget-rpi4-otg.html#post5910911
> 
> Details for alsa-lib are discussed in
> https://www.spinics.net/lists/alsa-devel/msg96781.html
> 
> 
> This is a solution I need - syncing the UAC2 gadget to master clock of
> real alsa soundcard . But again - I think the solution should be
> flexible to support any source of feedback information, be it in kernel
> or from userspace.
> 

Hi, please can we resume this discussion about the feedback endpoint?

Meanwhile a simple method described in
https://www.aktives-hoeren.de/viewtopic.php?p=137829&sid=0d6cd50e0f58618da33621c62e412ada#p137829
for obtaining required rate shift from /proc/asound/.../status to keep
the master side buffer optimally filled was tested. That could be one
source for the rate shift, to be passed to the driver. Perhaps a control
element like the "PCM Rate Shift" of the snd-aloop driver could be used.


Thanks a lot,

Pavel.