[alsa-devel] PROC_COEF/PROC_INDEX question

[Wu Fengguang]

On Fri, Aug 07, 2009 at 06:05:02PM +0800, Takashi Iwai wrote:
> At Fri, 7 Aug 2009 18:01:21 +0800,
> Wu Fengguang wrote:
> > 
> > On Fri, Aug 07, 2009 at 05:45:14PM +0800, Takashi Iwai wrote:
> > > At Fri, 7 Aug 2009 17:38:59 +0800,
> > > Wu Fengguang wrote:
> > > > 
> > > > Hello,
> > > > 
> > > > I'm not sure of the usage for GET_PROC_COEF/GET_COEF_INDEX, and found
> > > > that their return value is unstable (changing all the time) for codec:
> > > > 
> > > >         Codec: Realtek ALC888
> > > >         Address: 2
> > > >         Function Id: 0x1
> > > >         Vendor Id: 0x10ec0888
> > > >         Subsystem Id: 0x80860023
> > > >         Revision Id: 0x100202
> > > > 
> > > > For example:
> > > > 
> > > > # hda-verb /dev/snd/hwC0D2 0x20 GET_PROC_COEF 0 
> > > > nid = 0x20, verb = 0xc00, param = 0x0
> > > > value = 0x80
> > > > # hda-verb /dev/snd/hwC0D2 0x20 GET_COEF_INDEX 0
> > > > nid = 0x20, verb = 0xd00, param = 0x0
> > > > value = 0xe
> > > > # hda-verb /dev/snd/hwC0D2 0x20 GET_PROC_COEF 0 
> > > > nid = 0x20, verb = 0xc00, param = 0x0
> > > > value = 0x9c00
> > > > # hda-verb /dev/snd/hwC0D2 0x20 GET_COEF_INDEX 0
> > > > nid = 0x20, verb = 0xd00, param = 0x0
> > > > value = 0xf
> > > > 
> > > > I wonder if this is the normal case?
> > > 
> > > AFAIK, depending on the mode, the index is incremented automatically.
> > 
> > Ah, yes. That's in line with the above data.
> > 
> > When repeatingly call  GET_PROC_COEF, it returns some 'random' values:
> > 
> >         # hda-verb /dev/snd/hwC0D2 0x20 GET_PROC_COEF 0
> >         nid = 0x20, verb = 0xc00, param = 0x0
> >         value = 0x4f
> >         # hda-verb /dev/snd/hwC0D2 0x20 GET_PROC_COEF 0
> >         nid = 0x20, verb = 0xc00, param = 0x0
> >         value = 0x8000
> >         # hda-verb /dev/snd/hwC0D2 0x20 GET_PROC_COEF 0
> >         nid = 0x20, verb = 0xc00, param = 0x0
> >         value = 0x2520
> >         # hda-verb /dev/snd/hwC0D2 0x20 GET_PROC_COEF 0
> >         nid = 0x20, verb = 0xc00, param = 0x0
> >         value = 0x3e00
> 
> I guess it's not random but just the value of the next index.
> 
> > But when repeatingly call GET_COEF_INDEX, it returns the same value:
> > 
> >         # hda-verb /dev/snd/hwC0D2 0x20 GET_COEF_INDEX 0
> >         nid = 0x20, verb = 0xd00, param = 0x0
> >         value = 0xd
> >         # hda-verb /dev/snd/hwC0D2 0x20 GET_COEF_INDEX 0
> >         nid = 0x20, verb = 0xd00, param = 0x0
> >         value = 0xd
> 
> Reading the index itself doesn't increment the index.  Reading
> the coef value increases the index.  So is my understanding.

OK, so the coef read has some 'side effects', hehe.