[alsa-devel] USB asynchronous mode feedback format

[Julian Scheel]

Am Donnerstag, 14. Oktober 2010, 13:16:12 schrieb Daniel Mack:
> On Thu, Oct 14, 2010 at 01:01:52PM +0200, Julian Scheel wrote:
> > Am Donnerstag, 14. Oktober 2010, 12:48:55 schrieb Daniel Mack:
> > > On Thu, Oct 14, 2010 at 12:27:38PM +0200, Julian Scheel wrote:
> > > > thanks a lot! You made my day (c:
> > > > Using EP5 for feedback makes it working. So I now get the data out
> > > > even in async mode. Currently I have a problem left that channel
> > > > assignment jumps here and then. Probably a buffering issue...
> > > > Also neither a SRC4192  (sample rate converter) nor a PCM1794 (dac)
> > > > seem to be able to understand what I am sending right now... Not
> > > > sure why. Looking at the measurements it really looks like a proper
> > > > I2S signal.
> > > 
> > > Can you send oscilloscope screenshots? Which data format are you using?
> > 
> > Sure, attached you see a capture while running speaker-test to generate a
> > 1khz sine wave on one channel. (Blue: BCLK 1,536MHz, Yellow: LRCLK:
> > 48kHz, Green: I2S data)
> > If you want to see more/other captures just let me know what you need.
> 
> The dump doesn't show whether the LRCLK is symmetrical, iow, whether the
> low phase of LRCLK has the same number of BCLK cycles as the high phase.
> 
> But if that's the case, the signals do indeed look alright. Maybe you
> need the configure the codec to this format?

LRCLK is symmetrical. I use the modules from twistedpearaudio 
(http://www.twistedpearaudio.com/digital/metronome.aspx, 
http://www.twistedpearaudio.com/digital/cod.aspx) because this saved me some 
time designing a PCB for now...
They are configured through DIP switches - and I think correctly. For the SRC 
the settings are:
OWL0,1,2: 0, 0, 0 
OFMT0,1: 1, 0
MODE0,1,2: 1, 0, 0
IFMT0,1,2: 1, 0, 0
BYPASS: 0
LGRP: 0

What I am actually wondering about is, that the SRC produces some output even 
when the input is null. Attached is a picture of this case. I did not measure 
the BCLK this time.

Regards,
Julian
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