[mythtv-users] [mythtv] MythTV problems with current ALSA / Kernel 2.6.0

[Georg C. F. Greve]

Hi all,

I've seen some posts of people having problems with either current
versions of ALSA or with Linux Kernel 2.6.0 and mythTV.

Like the posting by Bob of Dec 17th, 2003:
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MythBackend Crashing    	
Hello,

Mythbackend seems to be crashing when trying to run with kernel 2.6 (It
seems to like my hardware a lot more, the kernel that is).. Here is the
backend..

2003-12-17 23:50:16 adding: zaius1 as a player 0
2003-12-17 23:50:16 MainServer::HandleAnnounce Playback
2003-12-17 23:50:16 adding: zaius1 as a player 1
2003-12-17 23:50:16 MainServer::HandleAnnounce Playback
2003-12-17 23:50:16 adding: zaius1 as a player 0
2003-12-17 23:50:16 MainServer::HandleAnnounce Playback
2003-12-17 23:50:16 adding: zaius1 as a player 0
2003-12-17 23:50:16 adding: zaius1 as a remote ringbuffer
2003-12-17 23:50:17 Changing from None to WatchingLiveTV
Cannot open DSP '/dev/dsp', dying.
open: Device or resource busy
Could not detect audio blocksize
Cannot open DSP '/dev/dsp', exitingopen: Device or resource busy
audio volume set to '65535'
Killed 
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After switching from Kernel 2.4.22 with external ALSA to Kernel 2.6.0
with included ALSA, I started seeing the same problems. 

As it seemed to be a pure problem of sound input/output, I tried to
take a look and found in the Linux kernel documentation (file
linux/Documentation/sound/alsa/ALSA-Configuration.txt):
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Proc interfaces (/proc/asound)
==============================

/proc/asound/card#/pcm#[cp]/oss
-------------------------------
  String "erase" - erase all additional informations about OSS applications
  String "<app_name> <fragments> <fragment_size> [<options>]"

   <app_name> - name of application with (higher priority) or without path
   <fragments> - number of fragments or zero if auto
   <fragment_size> - size of fragment in bytes or zero if auto
   <options> - optional parameters
          - disable   the application tries to open a pcm device for
                      this channel but does not want to use it.
                      (Cause a bug or mmap needs)
                      It's good for Quake etc...
          - direct    don't use plugins
          - block     force block mode (rvplayer)
          - non-block force non-block mode
          - whole-frag  write only whole fragments (optimization affecting
                        playback only)
          - no-silence  do not fill silence ahead to avoid clicks

  Example: echo "x11amp 128 16384" > /proc/asound/card0/pcm0p/oss
           echo "squake 0 0 disable" > /proc/asound/card0/pcm0c/oss
           echo "rvplayer 0 0 block" > /proc/asound/card0/pcm0p/oss

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Which made me guess that this could be a problem of mythTV not being
able to negotiate fragment size with the OSS/PCM of current ALSA
versions.

So I did

 /bin/echo "mythbackend 128 32768" > /proc/asound/card0/pcm0c/oss
 /bin/echo "mythbackend 128 32768" > /proc/asound/card0/pcm0p/oss

and it did the trick.

So all users of mythTV who had that problem might want to try this
themselves and the developers might want to add fragment negotiation
with current ALSA (or native ALSA support?)...

Hope this helps,
Georg


P.S. For completeness:

Debian GNU/Linux (mix of testing/unstable)

cat /proc/asound/version:

 Advanced Linux Sound Architecture Driver Version 0.9.7 (Thu Sep 25 19:16:36 2003 UTC).
 Compiled on Jan  4 2004 for kernel 2.6.0 (SMP).

intel8x0 chip/soundcard

mythTV 0.13

-- 
Georg C. F. Greve                                       <greve at gnu.org>
Free Software Foundation Europe	                 (http://fsfeurope.org)
Brave GNU World	                           (http://brave-gnu-world.org)
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