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

[zhigangw]

On 2018年05月18日 10:06, Pierre-Louis Bossart wrote:
>
>
> On 05/17/2018 08:30 PM, zhigangw wrote:
>>
>>
>> On 2018年05月17日 21:25, Pierre-Louis Bossart wrote:
>>> 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.
>>>
>>
>> Sorry! I think I miss one point in this description:
>> After I set the TFT = 4 hardcoded, the play can continue. If I follow 
>> the old code, the TFT = 16.
>> the XRUN will happen 100%, the DMA IRQ interval is less than 1ms,
>> the XRUN is caused by this.
>> the noise issue will be a next step, i will try keyon's patch later.
>
> Well yes, the FIFO is 16-deep so if you set TFT to 16 you essentially 
> have no sample left in the FIFO..
> Probably the formula should be TFT = min  (2 * active_tx_slot, 8); or 
> something along those lines.

Actually I have not got the the FIFO depth for all other platform, for 
lacking of documents.
I am not sure whether the TFT/RFT will be affected by sample-width or 
slot-number or both.
It need lots of experiment to confirm this if we can not get information 
from HARDWARE guys directly.
Thank you again Pierre for your comments.
Br
~zhigang
>>>>
>>>>
>>>> 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.
>>>
>> This is not related to DMA configuration, it is about the SSP 
>> configuration.
>> I did the experiment on my own APL-GPMRB, change the TFT will affect 
>> the DMA's IRQ interval.
>> I will check the DMA's configuration about the burst you mentioned.
>>
>> there is communication mechanism between the SSP and DMA,
>> when the TFT (FIFO threshold) is reached, the SSP will send request 
>> signal to DMA, the DMA will start to coping (into SSP's FIFO).
>> this mechanism is black to software level.
>> the TFT/RFT configuration determined when SSP sends request to DMA,
>>
>> thanks
>> br
>> ~zhigang
>>
>>>
>>>>
>>>>
>>>> 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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>>>
>>
>