[alsa-devel] Multiple codecs on one sound card for multi-channel sound card

[arnaud.mouiche at invoxia.com]

hello,

Le 17/09/2015 15:38, Caleb Crome a écrit :
> On Thu, Sep 17, 2015 at 1:51 AM, arnaud.mouiche at invoxia.com
> <arnaud.mouiche at invoxia.com> wrote:
>> Hello Caleb,
>>
>> freescale SSI is fine with more than 2 channels.
>> I have planed to publish a set of patch in this direction but we still have
>> some corner cases to fix first (rare issues with channels alignment)
>>
> I'd love to see anything you're willing to show :-)
>
>> Yet, this following is far enough to have it working.
>> And since the max/min rate is at the end the intersection of what the SSI,
>> the codec and the card are declaring, it will not change anything until you
>> connect the SSI to a codec with more than 2 channels, or a multi-codec
>> solution.
> What if I change channels_max to 16 for capture and playback?  Last
> time I tried, it would not keep the channels synchronized on the TDM
> bus.  I tried playing with the FIFO settings, which helped, but it
> still would not start each channel in the right slot reliably.
> Perhaps I was using an older kernel.
you put the finger on what's hurting !  ;)

In fact, we made 8 channels working in reliable way on imx50, with 
predictive latency  ... with an old kernel (3.17) ... based on freescale 
BSP... on sound/soc/imx/imx-ssi.c (something that doesn't exist outside 
freescale BSP)

Well, just to say it is doable on any recent imx since the hardware is 
not the issue. But the job was a set of awful hacks.

My plan was to re-do all this job on an upstream kernel, in a way it can 
be accepted.
Unfortunately you will have to wait, I'm under pressure for other stuff 
right now.

Regards,
arnaud

>
> I'll give it a try again.  Like I said, we'd love to get our
> 16-channel board up and running on the MX6, so I'm definitely
> motivated to put some work in to get it reliable.
>
> Thanks,
>   -Caleb
>