[alsa-devel] Invalid PCM pointer with CMI8738 and pcm.c buffer underuns

[Raymond Yau]

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/commit/sound/pci/cmipci.c?id=1c583063a5c769fe2ec604752e383972c69e6d9b

you have to dump the value of the register and increase the number of
trials to find out whether you can get a valid value


>
> >
> > state.CMI8738 {
> > control.1 {
> >
> > [...]
> >
> > Seem bug in adding channel map to iec958 instead of analog
>
> What does that mean? What should I do with those patches?
> Should I apply them and try to compile the latest ALSA version?

the patch did not channel map to the analog device

control.1 {
iface PCM
device 2
name 'Playback Channel Map'
value.0 0
value.1 0
value.2 0
value.3 0
value.4 0
value.5 0
comment {
access read
type INTEGER
count 6
range '0 - 36'
}
}

!!Aplay/Arecord output
!!--------------------

APLAY

**** List of PLAYBACK Hardware Devices ****
card 0: CMI8738 [C-Media CMI8738], device 0: CMI8738-MC6 [C-Media PCI
DAC/ADC]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: CMI8738 [C-Media CMI8738], device 1: CMI8738-MC6 [C-Media PCI 2nd
DAC]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: CMI8738 [C-Media CMI8738], device 2: CMI8738-MC6 [C-Media PCI
IEC958]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/commit/sound/pci/cmipci.c?id=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2

http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/conf/cards/CMI8738-MC6.conf;hb=HEAD

CMI8738-MC6.pcm.rear.0 {

         @args [ CARD ]
         @args.CARD {
                type string
         }
         type hw
         card $CARD
         device 1
}

device 0 seem emulate sb16 , you need to ask the author how this driver
support multi-channels

seem device 1 is used for multi-channels playback and device 2 is used for
iec958
>
>
> >
> > pcm.!default {
> >     type plug
> >     slave.pcm "dmixer"
> > }
> >
> > You need asym plugin for playback and capture when overwrite pcm.default
> >
>
> Should I change my /etc/asound.conf like in the examples here?
> http://alsa.opensrc.org/Asym
>

yes, you need define both playback and capture if you overwrite pcm.default
 since dmix does not support capture