[alsa-devel] PandaBoard ES Audio Problems

[Takashi Iwai]

At Thu, 31 Jan 2013 11:24:04 -0800,
Brent Weatherall wrote:
> 
> Clemens/Liam,
> 
>      Liam, I address your question below.  Clemens, stepping through the
> ALSA code, it seems the error *might* be in the ALSA code, but I am
> probably reading the code incorrectly:
> 
> pcm/interval.c:
> 
> 105 int snd_interval_refine_min(snd_interval_t *i, unsigned int min, int
> openmin)
> 106 {
> 107         int changed = 0;
> 108         if (snd_interval_empty(i))
> 109                 return -ENOENT;
> 110         if (i->min < min) {
> 111                 i->min = min;  <-- Is this statement reversed or do I
> not understand the code well enough?
> 112                 i->openmin = openmin;
> 113                 changed = 1;
> 114         } else if (i->min == min && !i->openmin && openmin) {
> 115                 i->openmin = 1;
> 116                 changed = 1;
> 117         }
> 118         if (i->integer) {
> 119                 if (i->openmin) {
> 120                         i->min++;
> 121                         i->openmin = 0;
> 122                 }
> 123         }
> 124         if (snd_interval_checkempty(i)) {
> 125                 snd_interval_none(i);
> 126
> 127         }
> 128         return changed;
> 129 }
> 130
> 
> Lines 110 - 113 appear to check if the hw params returned structure's
> minimum value (i->min) is less than the current min value (which is set to
> the requested rate in pcm.c:827  min = max = best).  Then if true, it
> appears to set the hardware reported min value to the current min, instead
> of the other way around.

The code is correct.  In general, hw_refine() code works like the
following:

- The configuration space begins with the full space

- When a hw constraint is given, it tries to shrink the configuration
  space to fit within the given constraint; it never expands in
  general (exceptions allowed, though, like in usb-audio's special
  code).

  This is the point you suggested in the  above.
  snd_internval_refine_min() tries to shrink the config space to fit
  wit with the condition (min <= i->min).

- Loop until all hw constraints are satisfied

- Then pick up either max or min value from the configuration space as
  the final value; it depends on the parameter type whether to pick
  max or min value


Takashi