On Wed, 13 Jan 2021 12:57:16 +0100,
Lauri Kasanen wrote:

On Mon, 11 Jan 2021 16:25:08 +0100
Takashi Iwai [off-list ref] wrote:

quoted

On Mon, 11 Jan 2021 13:02:22 +0100,
Lauri Kasanen wrote:

quoted

This order gives correct pointer advancing etc, but now it's hitting a
new problem: the pcm core is reusing the buffer from under the audio
card. It's writing new data to the area that is currently being read by
DMA.

Could you elaborate?  I still don't get what's going on there.

I figured it out. Turns out the hw registers were double-buffered in a
way that requires two periods' worth of buffers. The IRQ fires when one
buffer is finished and another is queued, not when everything is
finished as I first thought.

There doesn't seem to be a way to request the PCM core to keep two
periods' distance instead of one? I will deploy memcpy then.

We may return to the first approach, i.e. just use nextpos.  But then
snd_pcm_period_elapsed() has to be called right after the trigger
callback without the IRQ, because the trigger START already queued the
full period and the position advances.  So the first period-elapsed
has to be called from a work or such offload instead of IRQ.
In anyway, it's a bit tricky, yeah.


Takashi