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

[Roberto Fichera]

On 10/29/2015 04:54 PM, Caleb Crome wrote:
> On Thu, Oct 29, 2015 at 8:37 AM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>> On 10/29/2015 03:55 PM, Caleb Crome wrote:
>>> On Thu, Oct 29, 2015 at 6:44 AM, Caleb Crome <caleb at crome.org> wrote:
>>>> On Wed, Oct 28, 2015 at 9:53 PM, Nicolin Chen <nicoleotsuka at gmail.com> wrote:
>>>>> I am actually thinking about setting a watermark to a larger number.
>>>>> I forgot how the SDMA script handles this number. But if this burst
>>>>> size means the overall data count per transaction, it might indicate
>>>>> that each FIFO only gets half of the burst size due to dual FIFOs.
>>>>>
>>>>> Therefore, if setting watermark to 8, each FIFO has 7 (15 - 8) space
>>>>> left, the largest safe burst size could be 14 (7 * 2) actually.
>>>> Oh, does this depend on the data size?  I'm using 16-bit data, so I
>>>> guess the bursts are measured in 2 byte units?  Does this mean that
>>>> the burst size should be dynamically adjusted depending on word size
>>>> (I guess done in hw_params)?
>>>>
>>>>> Nicolin
>>> Okay, so wm=8 and maxburst=14 definitely does not work at all,.  wm=8,
>>> maxburst=8 works okay, but still not perfect.
>>>
>>> I just discovered some new information:
>>>
>>> With wm=8 and maxburst=8 (which is my best setting so far), I just
>>> captured a problem at the very start of playing a file, and restarted
>>> enough times to capture it starting wrong:
>>>
>>> Instead of the playback starting with
>>>
>>> (hex numbers:  my ramp file has first nibble as channel, second nibble as frame)
>>>
>>> frame 0:  00, 10, 20, 30, 40, 50, 60, 70, 80, 90, a0, b0, c0, d0, e0, f0
>>> frame 1:  01, 11, 21, 31, 41, 51, 61, 71, 81, 91, a1, b1, c1, d1, e1, f1
>>>
>>> It started with:
>>>
>>> frame 0:  00, 00, 10, 20, 30, 40, 50, 60, 70, 80, 90, a0, b0, c0, d0, e0
>>> frame 1:  f0, 01, 11, 21, 31, 41, 51, 61, 71, 81, 91, a1, b1, c1, d1, e1
>>>
>>> So, the transfer started wrong right out of the gate -- with an extra
>>> sample inserted at the beginning. Again, my setup is:
>>> 1) use scope to capture the TDM bus.  Trigger on first data change
>>> 2) aplay myramp.wav
>>> 3) If okay, ctrl-c and goto 2.
>>> 4) The capture below shows everything off by 1 sample.
>>>
>>> The capture is here:
>>> https://drive.google.com/open?id=0B-KUa9Yf1o7iOXFtWXk2ZXdoUXc
>>>
>>> This test definitely reveals that there is a startup issue.  Now for
>>> the $64,000 question: what to do with this knowledge?  I'm quite
>>> unfamiliar with how the DMA works at all.
>> I'm my case for example, I'm using a iMX6SX SoC, I've changed fsl_ssi.c to start the SSI
>> clock generated internally by setting both RDMAE and TDMAE just once I'm pretty sure
>> that everything has been setup (DMA and callback). Note that I'm not using alsa because,
>> my target is to integrate SSI in TDM network mode with my DAHDI driver for VoIP app.
>>
>> Back to the DMA question, in your case shouldn't be really a problem since all DMA
>> stuff is handled by the linux audio framework.
>>
>> Regarding my SSI problem, I was able to keep the DMA working for few second once before
>> it get stopped and never retriggered. Currently I've 2 DMA channel one for TX and another for RX
>> I've changed my DTS and update my fsl_ssi to handle new clocks, I guess only the CLK_SPBA
>> has improved my situation. I've also tried to enable both RIE and TIE to service the ISR, with
>> and without SSI DMA support, but this end with a full system freeze.
> I got this system freeze too when enabling RIE and TIE because the
> interrupts TFE1IE, TFE0IE, TDE1IE, TDE0IE are *enabled* at reset.
> (Check ref manual 61.9.5).   which I suspect was a livelock kind of
> situation where the ISR is just called infinitely often.  After
> disabling those, then the system worked okay.  Check out the previous
> patch I sent on the issue yesterday or the day before.

Ooohh!!! Forgot to check this!!! I'm now going to mask them!!!

>
>> Another thing I'm looking is the sdma events (37 and 38) which are reported by the reference
>> manual to
>>
>> 37 -> SSI1 Receive 0 DMA request
>> 38 -> SSI1 Transmit 0 DMA request
>>
>> along that there are also
>>
>> 35 -> SSI1 Receive 1 DMA request
>> 36 -> SSI1 Transmit 1 DMA request
>>
>> I don't know actually how the two events types will behaves from the SDMA point of view.
> The 35 and 36 are for Dual fifo mode only, and no current system (with
> fsl_ssi.c anyway) uses dual fifo mode.  How do I know?  Because the
> it's definitely broken in the fsl_ssi.c.  I was just about to report
> that bug.

Ah! Thanks! The reference manual is really clear to explain it :-D !

> hint:  fsl_ssi.c:  if (ssi_private->use_dma && !ret && dmas[3] ==
> IMX_DMATYPE_SSI_DUAL) {
> should read  if (ssi_private->use_dma && !ret && dmas[4] ==
> IMX_DMATYPE_SSI_DUAL) {

Yep! I know such piece of code.

>
>> I'm also considering to make plain new audio driver to at least try to use something which
>> is supposed to work fine with SSI.
> Yeah, maybe that's the easiest way to go just to get operational.
> Start with just the bare minimum ssi driver so you know all the
> registers are locked into place the way you like.
>
> -caleb
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