[clug] alsa config for MythTV (spdif)

Paul mylists at wilsononline.id.au
Tue Jan 5 03:52:28 MST 2010

On 5/01/2010 6:17 PM, Jeff Stiff wrote:
> 2010/1/5 Paul <mylists at wilsononline.id.au
> <mailto:mylists at wilsononline.id.au>>
>     In the last few months even after upgrading MythTV and Fedora
>     (currnetly 12), I have been getting these " WriteAudio: buffer
>     underrun" messages in my Mythfrontend log which causes pauses during
>     playback.
>     So I'm trying to review my ALSA setup which I admit I just copied
>     from the Wiki, so if anyone has some advice I would be glad to hear it.
>     I'm using an on board nvidia sound card which I'm outputting my
>     SPDIF to my AMP.
>     Note the current setup does produce sound and it seems good to me
>     but perhaps if there is a way to optimise the buffers perhaps this
>     might fix the issue I have with the buffer underrun.
>     # cat /etc/asound.conf
>     #Generated by system-config-soundcard
>     #If you edit this file, don't run system-config-soundcard,
>     #all your changes here could be lost.
>     #SWCONF
>     #DEV 0
>     defaults.pcm.card 0
>     defaults.pcm.device 0
>     defaults.ctl.card 0
> Sorry Paul, I can not help with the asound.conf file, as none of my Myth
> machine (3) have that file.  However, I do wonder if the pauses are
> caused by the buffer underrun you reported. As my logs are full of the
> same WriteAudio: buffer underrun message, they seem to be a few seconds
> apart, but I do not notice any pause when watching anything, including HD.
> I seem to recall something to do with the video causing stuttering, I
> will have a look to see if I can find what that was.  But I would
> probably stop looking at the audio at present, and focus more on the
> video settings.
> Hope this helps,
> Jeff.

note I'm using the atrpms (Nvidia package)

I don't see any output in Dmesg about the onboard sound card but the Nvidia driver seems 
to initialise ok:

nvidia: module license 'NVIDIA' taints kernel.
Disabling lock debugging due to kernel taint
firewire_core: created device fw0: GUID 0014855600244bd2, S800
forcedeth 0000:00:0a.0: ifname eth1, PHY OUI 0x3f1 @ 7, addr 00:14:85:22:c9:03
forcedeth 0000:00:0a.0: highdma csum gbit lnktim desc-v3
i2c-adapter i2c-3: nForce2 SMBus adapter at 0x1c00
i2c-adapter i2c-4: nForce2 SMBus adapter at 0x1c40
cx88/2: cx2388x MPEG-TS Driver Manager version 0.0.7 loaded
cx88/0: cx2388x v4l2 driver version 0.0.7 loaded
nvidia 0000:05:00.0: PCI INT A -> Link[APC3] -> GSI 18 (level, low) -> IRQ 18
nvidia 0000:05:00.0: setting latency timer to 64
NVRM: loading NVIDIA UNIX x86 Kernel Module  190.42  Tue Oct 20 20:18:32 PDT 2009

I think this maybe the sound card:

Intel ICH 0000:00:04.0: PCI INT A -> Link[APCJ] -> GSI 22 (level, low) -> IRQ 22
Intel ICH 0000:00:04.0: setting latency timer to 64
intel8x0_measure_ac97_clock: measured 50995 usecs (2512 samples)
intel8x0: clocking to 46773

I had to add these to my modprobe some time ago to avoid the sound device on my tuner 
initialising before the mainboard sound card:

# onboard sound card: NFORCE - NVidia CK804
options snd cards_limit=8
alias snd-card-0 snd-intel8x0
options snd-intel8x0 index=0
alias snd-card-7 snd-usb-audio
options snd-usb-audio index=7

# DNTV  sound capture device CX88x - Conexant CX8801
options cx88xx card=42
options cx88_alsa index=1
alias snd-card-1 cx88_alsa
alias sound-slot-1 cx88_alsa

and there is some old code which I'm not sure which I should remove from and older Fedora 
install .

#remove snd-intel8x0 { /usr/sbin/alsactl store 0 >/dev/null 2>&1 || : ; }; /sbin/modprobe 
-r --ignore-remove snd-intel8x0
#install snd-intel8x0m { /sbin/modprobe snd-intel8x0; } ; /sbin/modprobe --first-time 
--ignore-install snd-intel8x0m


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