[alsa-devel] USB asynchronous mode feedback format

Julian Scheel julian at jusst.de
Mon Oct 18 18:53:49 CEST 2010

Am Freitag, 15. Oktober 2010, 11:03:21 schrieb Daniel Mack:
> On Fri, Oct 15, 2010 at 10:59:32AM +0200, Julian Scheel wrote:
> > Am Donnerstag, 14. Oktober 2010, 17:39:13 schrieb Daniel Mack:
> > > Well, even if it was, you should hear some sound. It might be
> > > distorted, but if you don't get any output, the reason is somewhere
> > > else.
> > > 
> > > Did you check the schematics of your board in comparison to the
> > > reference diagrams in the codec's datasheet? Are there any other things
> > > to be considered maybe?
> > > 
> > > What about the voltage levels? Are they within the specs? I had a quick
> > > look and it seems that Vdd on the codec has to be within 3.0 .. 3.6V,
> > > while the signals you provide rather seem to be in the range of 5V? The
> > > absolute maximum ratings say that Vdd must not be greater than 4.0V.
> > 
> > Sorry for one more off-topic mail, but I rechecked it. Digital Input
> > Voltage is -0.3V to 6.5V, so my 5V clock voltage should be fine imho.
> > Vdd is 3.0V on my board...
> > Do you maybe have any other thoughts what might be wrong here?
> No, sorry. I think you're doing the right thing by analyzing the digital
> stream carefully and checking the electrical components around the
> codec. There's usually a ton of things to consider, but it's hard to
> tell what to look for without having the same hardware.
> Still, let me know what you find :)

Just figured out what went wrong. The PCM1794A requires the I2S signal to 
contain 24 bit. So when running in 16 bit mode one has to fill up with 8 zero 
bits. Now I doubled the BCLK so that I would be able to send 32 bit to the 
DAC. Still am fighting a bit with the AT91's SSC controller to send only one 
package per L/R frame, but in general I am seeing a proper signal behind the 
DAC now!


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