[Sound-open-firmware] how to find a suitable value for the TFT/RFT parameter on multi-platform

[Pierre-Louis Bossart]

On 5/17/18 4:31 AM, zhigangw wrote:
> Hello Liam:
> 
>          I think it is better to mention this status again in the mail 
> list.
> 
> I am working on playback with the TDM8(4slot used)-48KHz-32bit on 
> APL-GPMRB platform.
> 
> Currently the status is:
> 
> The music can be heard from the all four channels.
> 
> But the it has the noise on the background. the noise exists all the 
> time during playing.
> 
> No xrun happened during the audio playing.
> 
> I have not tried the pause/resume feature.
> 
> I have not tried keyon's patch for the noise issue.

Looks to me like you've answered to your own question:
if there is no xrun, the problem is not related to TFT settings, so 
please try with known workarounds to remove the noise issue.

> 
> 
> Issue:
> 
> During the development, the TFT (in SSP's SSC3 register) parameter will 
> affect the playing operation.
> 
> If we keep code: tft = active_tx_slots * 4;  the tft will be 16.
> 
> during the playing, i found the DMA IRQ will happened very frequently, 
> less than 1ms,
> 
> which will cause XRUN during playing. But it will be normal if the tft 
> value is below 8 (tft < 8).

Doesn't this point to a DMA configuration issue? the IRQ should only 
come after a set of burst transfers related to the TFT settings. In 
other words, if you reduce TFT you should increase the number of bursts 
to keep the IRQ rate constant.

There is a clear note in the code on this btw, the RFT/TFT settings 
cannot be modified in isolation, you need to have a related change on 
the DMA side.


> 
> 
> I did some tests on other platform. but I have not found suitable way to 
> fit all of them.
> 
> the RFT also have the similar concern.
> 
> 
> Do you have any suggestions about this?
> 
> 
> thank you
> 
> br
> 
> ~zhigang
> 
> 
> 
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