[alsa-devel] fsl_ssi.c: Getting channel slips with fsl_ssi.c in TDM (network) mode.

[Caleb Crome]

On Wed, Oct 21, 2015 at 12:32 AM, arnaud.mouiche at invoxia.com
<arnaud.mouiche at invoxia.com> wrote:
>
>
> Le 20/10/2015 19:43, Caleb Crome a écrit :
>> Hi Arnaud,
>>    My root filesystem already had that firmware in it (the kernel
>> didn't have the kernel patch, but when I applied that patch, the
>> generated sdma script was identical.
>>
>> So, unfortunately, that's not the problem with the channel slipping.
>> Any other thoughts on why the channel would slip?  Or pointers on how
>> to diagnose?  I have an oscilloscope & know how to use it :-)  Also, I
>> can flip a GPIO to watch for timing of interrupts, etc (although I
>> haven't done that yet).
>>
>>
>> Thanks,
>>    -Caleb
>
>
> Hello Caleb,
>
> In your situation, I would:
> - check if TUE0/1 flag never rise (Transmitter Underrun) by activating the
> TUE0/1IE bit to generate related interrupts. It looks like already enabled
> in 4.0 by collecting statistics with fsl_ssi_dbg_isr(). Despite there is no
> printk message on underrun, stats can be read from
> /sys/kernel/debug/xxxx.ssi/stats.

Heh, I checked that and I couldn't get the fsl_ssi_dbg_isr to trigger
ever, for any reason.  Somehow interrupts seem to be disabled in the
SSI driver, and I can't figure out how to enable them.  It appears
that the only interrupt required is the DMA interrupt, and SSI
interrupts are not checked.    The /sys/kernel/debug/xxxx.ssi/stats
file reads all zeros no matter what, even during playing, and even
after the user space detects underruns.

>
> - I suspect the dma is not fast enough to fill the FIFO. may be you should
> dig to check how SDMA priority are configured amongs the differents DMA
> channels.
> Not something I already look at before. A quick look suggest that
> DMA_PRIO_HIGH is _NOT_ configured by the fsl_ssi.c driver (wheras the
> imx-ssi.c did)


Ah ha!  Perhaps that's it.  I will check into that.  Maybe that's the
root cause.  Thanks so much.

-Caleb


>
> Regards,
> Arnaud
>
>