[alsa-devel] [PATCH 0/5] ASoC: davinci: Use edma-pcm and remove davinci-pcm

[Mike Looijmans]

On 04-03-15 15:10, Peter Ujfalusi wrote:
> On 03/04/2015 02:28 PM, Mike Looijmans wrote:
>>> W/o the AFIFO enabled OMAP-L138 should be close enough for the platforms which
>>> does not have FIFO. But I can test w/o FIFO and w/ FIFO on this platform.
>>
>> Okay, I hadn't even thought of simply disabling the FIFO. Good to know you
>> already took this into consideration, good work.
>
> Do you have possibility of testing the edma-pcm in your setup by any chance?

Not really, since the board has some TI hardware that doesn't work on newer 
kernels. The 1271 Wifi chip for one, that stopped working after 3.2.

>> BTW, I simply linked the params for the McASP-to-DDR in a big loop for my
>> 2.6.37 based kernel, which solved the problems when sampling 16 channels.
>
> Sounds interesting, is it possible to share this code with me so I can see
> what you have done and I can check if your use case will work with the
> edma-pcm as well?

Sure, though I think I've posted it before.

What I did was just create a set of params in a closed circle, each pointing 
to the next, and the last pointing to the first. This means you'll need as 
many param slots as there are periods though. I typically use 8, but as few as 
2 will do as well (which is what ping-pong does into the SRAM).

The IRQ handler is then reduced to emit just the "period" signal. There's no 
hard timing requirement to the IRQ handler, user space just needs to grab (or 
fill) the data before the DMA loops around. (This allows for very short 
periods too, if low latency is your goal, since missing one or even several 
interrupts won't harm the transfer.)

I set up the DMA to use larger chunks by only triggering once every ~16 words, 
so that the "a" parameter of the param can be set much larger, and hence the 
bytes-per-period can be set to values beyond 64k. So the McASP only sends out 
one event every 16 words, and the DMA is set up accordingly.

I use a 4MB buffer for that 16-channels-of-32-bits system, usually with 8 
periods of 512kB each.


Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


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