[alsa-devel] fsl_ssi.c: Roberto's problem: ssi hangs after some number of samples

[Roberto Fichera]

On 11/04/2015 06:58 PM, Nicolin Chen wrote:
> On Wed, Nov 04, 2015 at 04:33:16PM +0100, Roberto Fichera wrote:
>  
>> With the patch below I'm able to see the error happening. And more likely it happen just just afterwards
>> the EVTERR notify the problem to the ISR. At this point the DMA simply stalls due to some problems, most
>> likely because the SSI FIFO is in overflow or underflow condition. I will do add the code to dump the SSI
> No, SSI FIFO under/overflow were caused by the DMA stall as their
> channels got error out -- SSI was still consuming the TX FIFO and
> filling the RX FIFO while DMA didn't move the data at all so SSI
> FIFOs got under/overflowed.

Yeah! The SSI is correctly reporting this problem because DMA is stalled for some reason.

>
>> I think that at this point we should in theory restart the DMA channel, but however how to fix this and
>> why this is happening?
> According to Reference Manual:
> ----
>
> 1) The CHNERR[i] bit is set when a DMA request that triggers channel
> i is received through the corresponding input pins and the EP[i]
> bit is already set;
>
> 2) Externally triggered channel pending flag EP[i] is set by the
> scheduler when the channel was activated by a DMA request. It can
> be cleared by the ith channel script.
>
> ----
>
> It looks like your system made another DMA request while the SDMA
> was still in the middle of the transaction for the same channel.

I don't know because this is something I cannot control. I'm just setting up 2 cyclic dma
for both TX and RX before to set both RDMAE and TDMAE and nothing else. The rest
is done by the SDMA ISR.

> I guess you should find a way to make less frequent DMA requests,
> making higher watermarks and larger burst size for example.
>
I can try to increase the FIFO watermark up to 15 elements, but after that
I don't have more choices. The problem is that the TDM has to run continuously
because the SLIC need it. I can eventually enable and disable the DMA requests
depending by the active channels for optimization, but the problem still,why the
DMA transfer is not triggered?