[alsa-devel] Query on Audio DMA using DMAEngine

[Mark Brown]

On Thu, Jul 04, 2013 at 08:06:34AM +0200, Mike Looijmans wrote:

> In any case, using the IRAM directly might have some use, because
> you don't have to compete for the DDRRAM with other devices. But I
> never understood what the ping-ping via IRAM was supposed to
> accomplish, I don't see why McASP -> IRAM -> DDRRAM (or the other
> way around) would be better than just McASP -> DDRRAM. Especially
> since the McASP has a built-in 256 byte FIFO buffer on both
> channels. In all my measurements, using the IRAM ping-pong only made
> things worse in terms of overruns and underruns, not better.

> Anyone who know why the ping-pong was implemented and what kind of
> usage it was intended for?

Pushing the audio through some static RAM is normally implemented in
order to save power - when doing this you can put the dynamic RAM into a
lower power state for more of the time, only waking it up to burst data
to or from the static RAM (assuming an otherwise idle system).  This is
more normally used for playback than for capture but the same idea
applies in both cases.
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