[alsa-devel] How to use implicit feedback with full duplex?

[Eldad Zack]

On Wed, 6 Feb 2013, Clemens Ladisch wrote:

> Eldad Zack wrote:
> > On Tue, 5 Feb 2013, Clemens Ladisch wrote:
> >> I thought I'd try to use implicit feedback with my simple audio device:
> >> [...]
> >> This works fine when playing something:
> > ...
> >> But when I then try to record at the same time, the driver refuses to
> >> configure the input endpoint (to the only format, which is already set):
> >> And despite that "alreay in use" check, the input endpoint is affected
> >> so much that playback breaks.
> >>
> >> Is full duplex supposed to work?  Does it work with other devices?
> >
> > This is probably a "yes, but" :)
> > I use my device mostly full duplex, but with jack opening both
> > playback and capture at the same time.
> >
> > I assume you are opening two different streams, one for playback and
> > one for capture.
> 
> Jack *also* uses two different streams, but it opens them at the same
> time.

Oh, right. 

> 
> > Can you try using jackd -d alsa -d hw:x with the device and see if that
> > works for you?
> 
> That works.  This means that there is a race condition in the driver, or
> that the different open/hw_params/prepare order trips it up.

Hmm. I seem to have tested this wrong the other day or just had luck (I 
tried it just once).
But today I can trigger breaking the playback when opening capture 
later every time I try, just like you described.

I get this too when the audio breaks:
[  766.987497] xhci_hcd 0000:00:14.0: shutdown urb ffff880244f89600 ep1in-iso
[  766.987510] xhci_hcd 0000:00:14.0: shutdown urb ffff880244f89400 ep1in-iso
[  766.987519] xhci_hcd 0000:00:14.0: shutdown urb ffff8802438e6000 ep1in-iso
[  766.987527] xhci_hcd 0000:00:14.0: shutdown urb ffff8802438e6200 ep1in-iso
[  766.987534] xhci_hcd 0000:00:14.0: WARN Event TRB for slot 1 ep 2  with no TDs queued?
[  766.987550] xhci_hcd 0000:00:14.0: shutdown urb ffff8802438e6400 ep1in-iso
[  766.987562] xhci_hcd 0000:00:14.0: shutdown urb ffff880244f89000 ep1in-iso
[  766.987576] xhci_hcd 0000:00:14.0: shutdown urb ffff880244f89200 ep1in-iso
[  766.987584] xhci_hcd 0000:00:14.0: shutdown urb ffff880244f88800 ep1in-iso

I will try to figure out what's happening on the weekend.

Cheers,
Eldad