Re: running 32 chan AD/DA on Linux

Re: running 32 chan AD/DA on Linux

[Daniel Mack]

Hi Igor,

please don't remove the alsa ML from Cc:.

On 11.03.2013 09:37, Igor Levin wrote:

[...]

> But now we got a bit of a breather and our developers are finally able
> to give Linux the attention it deserves
> to get it going. I have couple fundamental question which you guys can
> help us with:
> 
> 1) Does Linux audio support the Implicit feedback mode where the Out
> pipe will source the same amount of
>      samples as are coming into related IN pipe.

Yes.

>  This is the sync mode
> we use in Orion 32. If this is so, could
>     you kindly provide the file/line number in the source code where we
> can see how it makes the packetising
>      decision.

Please have a look at sound/usb/endpoint.c - this is where the packet
logic lives in. Please read the comments in this file - the packet
sending for this implicit feedback mode is implemented in
queue_pending_output_urbs().

> 2) We are upgrading our Zodiac DAC to use asynchronous feedback mode.
> What Async feedback mode formats
>      does Linux support? Where can we see it in the source?

Linux supports feedback over dedicated isochronous endpoints as well.
The format is auto-detected in snd_usb_handle_sync_urb(), also in
sound/usb/endpoint.c, after each stream start. Internally, the driver
uses Q16.16.

Hope this helps. In case of more specific questions, please just let me
know.


Thanks,
Daniel

Re: running 32 chan AD/DA on Linux

[Daniel Mack]

Hi Igor,

On 11.03.2013 09:56, Igor Levin wrote:
> Thank you so much for a quick answer, are you in Europe by any chance?

Yes, in Germany.

> Could you give us a link where we can browse the source code on the Net, 
> or tell us where to get those files
> mentioned as there seem to be so many Linux source files floating in the 
> web. Please forgive my ignorance
> if this question seems so naive, I am really a hardware engineer :)

There's Linus' repository which ends up in the official tarball releases
on a regular basis. You can browse that tree online in its cgit:


https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/sound/usb/

> Do you believe the code base as it stands will work with 32 channels 
> In/Out pipes or do we need to
> get the unit to one of you guys to test it and make corrections as needed?

I'm not aware of any sound specific limitations in that area. Just try
it, and let us know how it goes. Sending the output of 'lsusb -v' for a
descriptor dump is mandatory in order to understand how your device is
designed.


Thanks,
Daniel