[alsa-devel] [Q] ASoC: What's the real meaning of SND_SOC_DAIFMT_NB_NF?

Mark Brown broonie at opensource.wolfsonmicro.com
Fri Feb 24 12:20:39 CET 2012

On Fri, Feb 24, 2012 at 08:53:11AM +0100, javier Martin wrote:

> In the piece of code I've shown to you, when someone configures
> (SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF) he's really selecting an
> active high frame clock when the standard says just the opposite
> (wm8974 datasheet p50).

> If I fixed the bug in the SSI I would break both of them, since I
> would be changing frame clock polarity.

No, with I2S the main effect of inverting the frame clock is to cause a
left/right swap which is a relatively subtle issue, it's not obvious on
an immediate listening test.  It's not really active high or active low
but rather indicating which channel the sample is.
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