[alsa-devel] Questions about virtual ALSA driver (dummy), PortAudio and full-duplex drops (playback)

Smilen Dimitrov sd at imi.aau.dk
Fri Aug 16 07:20:08 CEST 2013

Hi Raymond,

Many thanks for your response!

>> While I have learned that modern cards do not have on-board buffers,
> Take a look at Intel® High Definition Audio Specification Document Change
> Notification
> 4.6 Energy Efficient HD Audio (EEAudio) Mechanism
> There is controller (HW) buffer <local fifo> in the Figure 14 HD Audio DMA
> and buffering

Thanks for spotting that - wasn't aware of this document. I had a bit of trouble tracking it down using those terms - ended up finding it on a page entitled "Intel® High Definition Audio Energy Efficient Buffering: Spec".

Now, that comment of mine, stems from this:

>>> I'm assuming that the card has it's own intern capture buffer memory
>>> on board;
>> No modern card has this.  All data is immediately read from/written to
>> main memory.
> Thanks for noting this - I wish I knew better :) [...]

... and come to think of it, I did start the discussion referring to "capture" there. Reading the Intel spec DCN, "capture" is never mentioned, while "played" is mentioned once. Does this mean that the referred FIFO for hda-intel is just for playback, while there is no such counterpart for capture? Or is it that for hda-intel on-board cards, they have FIFO's in both direction, but other modern cards don't necessarily? Or maybe I introduced the problem, by carelessly referring to "buffer memory", which might mean true random access memory - while modern cards may have FIFO's (which I'd guess are electrically simpler)?

Thanks for any clarifications,

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